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TSSA Gas Technician 2 (G2) study materials
TSSA Gas Technician 2 (G2) study resources

TSSA Gas Technician 2 (G2) practice questions

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Question 1Gas fundamentals and properties of gases

A technician reads a natural gas meter and needs to convert a volume of gas to its heat content. Which property directly expresses the heat released by burning a unit volume of the gas?

  1. Wobbe index
  2. Specific gravity
  3. Heating value Correct answer.
  4. Compressibility factor

Explanation

Heating value (calorific value) is the quantity of heat released when a unit volume or mass of gas is completely burned, usually expressed in MJ/m³ or BTU/ft³. It is the property used to relate metered gas volume to delivered energy. Specific gravity, compressibility, and Wobbe index describe other characteristics and do not by themselves state heat per unit volume.

Question 2Gas fundamentals and properties of gases

Natural gas supplied through distribution systems is principally composed of which compound?

  1. Methane Correct answer.
  2. Butane
  3. Propane
  4. Carbon monoxide

Explanation

Pipeline natural gas is predominantly methane, typically in the range of roughly 90 percent or more by volume, with smaller amounts of ethane, propane, and inert gases such as nitrogen and carbon dioxide. Methane's high hydrogen-to-carbon ratio gives it clean combustion and a high heating value per unit mass. The other listed gases appear only in trace or blended quantities.

Question 3Gas fundamentals and properties of gases

A technician must detect a gas leak at a joint. Which physical property of natural gas makes it detectable by the odorant added at the distribution level?

  1. It is lighter than air and rises quickly
  2. It burns with a visible yellow flame
  3. It is odorless in its raw state, so a mercaptan is added Correct answer.
  4. It condenses readily at ambient temperature

Explanation

Raw natural gas is essentially odorless, so distribution utilities inject an odorant such as mercaptan or a sulfur-based blend to make leaks perceptible at concentrations well below the lower explosive limit. This odorization is a safety requirement tied to the gas's lack of natural smell. The other options describe unrelated properties.

Question 4Gas fundamentals and properties of gases

Which value represents the lower explosive limit (LEL) commonly cited for natural gas in air?

  1. About 5 percent by volume Correct answer.
  2. About 25 percent by volume
  3. About 15 percent by volume
  4. About 1 percent by volume

Explanation

Natural gas has a flammable range in air of roughly 5 to 15 percent by volume, with about 5 percent being the lower explosive limit and 15 percent the upper explosive limit. Below the LEL the mixture is too lean to ignite, and above the UEL it is too rich. Combustible gas detectors are commonly calibrated to alarm at a percentage of the LEL.

Question 5Gas fundamentals and properties of gases

A technician compares the density of natural gas with air. Which statement correctly describes specific gravity as applied to fuel gases?

  1. It is the ratio of gas density to water density at 4 °C
  2. It is the ratio of gas heating value to air heating value
  3. It is the ratio of gas density to air density at the same conditions Correct answer.
  4. It is the mass of gas per unit pressure at standard temperature

Explanation

Specific gravity of a gas is the ratio of its density to that of air at the same temperature and pressure. Air is assigned a value of 1.0, and natural gas is lighter than air at approximately 0.6. This ratio governs how the gas behaves if released, whether it rises or accumulates at low points.

Question 6Gas fundamentals and properties of gases

A technician is working near a pit and must know how propane behaves if released. Propane has a specific gravity of about 1.5 relative to air. What does this mean for accumulation?

  1. It rises and dissipates at ceiling level
  2. It tends to settle and collect in low areas Correct answer.
  3. It is neutrally buoyant in air
  4. It stays fully mixed with air at all heights

Explanation

A gas heavier than air, with specific gravity above 1.0, sinks and accumulates in low-lying areas such as pits, basements, and sumps. Propane at about 1.5 is heavier than air, so released vapour collects at the lowest available point. This drives ventilation and ignition-source precautions for LPG work.

Question 7Gas fundamentals and properties of gases

Which statement correctly describes the relationship between absolute pressure and gauge pressure?

  1. Absolute pressure equals gauge pressure plus atmospheric pressure Correct answer.
  2. Gauge pressure equals absolute pressure plus atmospheric pressure
  3. Gauge and absolute pressure are identical when the system is pressurized
  4. Absolute pressure equals gauge pressure minus atmospheric pressure

Explanation

Gauge pressure is measured relative to local atmospheric pressure, while absolute pressure is measured relative to a perfect vacuum. Therefore absolute pressure equals gauge pressure plus atmospheric pressure. Gas laws and capacity calculations use absolute pressure, so the atmospheric addition must not be omitted.

Question 8Gas fundamentals and properties of gases

A gas exerts a gauge pressure of 35 kPa. Assuming standard atmospheric pressure of about 101 kPa, what is the absolute pressure in kPa?

  1. 66 kPa
  2. 136 kPa Correct answer.
  3. 35 kPa
  4. 101 kPa

Explanation

Absolute pressure is gauge pressure plus atmospheric pressure, so 35 kPa plus 101 kPa equals 136 kPa. Absolute pressure is required whenever a gas law calculation is performed, because those laws assume a zero reference at perfect vacuum. Reporting the gauge value alone would understate the actual pressure.

Question 9Gas fundamentals and properties of gases

According to Boyle's law, what happens to the volume of a fixed mass of gas at constant temperature when the absolute pressure is doubled?

  1. The volume doubles
  2. The volume increases four times
  3. The volume remains unchanged
  4. The volume is halved Correct answer.

Explanation

Boyle's law states that at constant temperature the volume of a fixed mass of gas is inversely proportional to its absolute pressure. Doubling absolute pressure therefore halves the volume. The relationship applies only when absolute pressure is used, not gauge pressure.

Question 10Gas fundamentals and properties of gases

A gas sample occupies 2.0 m³ at 300 kPa absolute. If the temperature is held constant and the pressure is reduced to 150 kPa absolute, what is the new volume?

  1. 2.0 m³
  2. 1.0 m³
  3. 3.0 m³
  4. 4.0 m³ Correct answer.

Explanation

Using Boyle's law, P₁V₁ equals P₂V₂. Here 300 kPa times 2.0 m³ equals 600 kPa·m³, and dividing by 150 kPa gives 4.0 m³. Halving the pressure doubles the volume for a fixed mass at constant temperature.

Question 11Gas fundamentals and properties of gases

Charles's law describes the behaviour of a fixed mass of gas at constant pressure. Which statement is correct?

  1. Volume is independent of temperature
  2. Volume is directly proportional to gauge pressure
  3. Volume is directly proportional to absolute temperature Correct answer.
  4. Volume is inversely proportional to absolute temperature

Explanation

Charles's law states that at constant pressure the volume of a fixed mass of gas varies directly with its absolute temperature. Heating the gas makes it expand; cooling makes it contract. The temperature must be expressed in kelvin, since the relationship fails if Celsius values are used directly.

Question 12Gas fundamentals and properties of gases

A confined gas volume is heated from 300 K to 450 K at constant pressure. What happens to its volume?

  1. It doubles
  2. It stays the same
  3. It increases to 1.5 times the original Correct answer.
  4. It decreases to two thirds of the original

Explanation

Because volume is proportional to absolute temperature at constant pressure, the ratio of new to old temperature is 450 divided by 300, which equals 1.5. The volume therefore becomes 1.5 times the original. Using Celsius temperatures here would give an incorrect result.

Question 13Gas fundamentals and properties of gases

The general gas law combines pressure, volume, and temperature for a fixed mass of gas. Which expression correctly represents the relationship between two states?

  1. P₁/T₁ = V₂/T₂
  2. P₁V₁ = P₂V₂T₂/T₁
  3. P₁V₁/T₁ = P₂V₂/T₂ Correct answer.
  4. P₁V₁T₁ = P₂V₂T₂

Explanation

For a fixed mass of gas, the ratio PV/T remains constant, so P₁V₁/T₁ equals P₂V₂/T₂. This combined relationship reduces to Boyle's law when temperature is constant and to Charles's law when pressure is constant. Temperatures must be absolute.

Question 14Gas fundamentals and properties of gases

Which statement best describes the behaviour of an ideal gas according to the kinetic theory?

  1. Gas molecules attract each other strongly and occupy fixed positions
  2. Gas molecules form a continuous incompressible fluid
  3. Gas molecules are stationary and transfer heat only by conduction
  4. Gas molecules move randomly and collide elastically with negligible intermolecular attraction Correct answer.

Explanation

The kinetic theory models an ideal gas as molecules in constant random motion, with elastic collisions and negligible intermolecular forces and molecular volume. Pressure arises from molecular impacts on the container walls, and temperature reflects average kinetic energy. Real gases deviate from this model near condensation conditions and at high pressure.

Question 15Gas fundamentals and properties of gases

A technician observes that a gas cylinder feels cooler as gas is rapidly released. Which principle explains this?

  1. The gas's specific gravity increases during release
  2. The heating value of the gas decreases during release
  3. Expansion of a gas does work and reduces its internal energy Correct answer.
  4. The gas absorbs heat from the cylinder walls only

Explanation

When gas expands rapidly it does work on its surroundings, and the energy for that work comes from the gas's internal energy, lowering its temperature. This adiabatic cooling effect is why frost can form on valves during rapid release. Heat transfer from the cylinder walls is a secondary effect, not the cause.

Question 16Gas fundamentals and properties of gases

Which gas law states that the total pressure of a mixture of non-reacting gases equals the sum of the partial pressures of the individual gases?

  1. Charles's law
  2. Gay-Lussac's law
  3. Boyle's law
  4. Dalton's law Correct answer.

Explanation

Dalton's law of partial pressures states that in a mixture of non-reacting gases, the total pressure is the sum of the pressures each gas would exert alone in the same volume. This is useful when blended gases such as natural gas with inert nitrogen and carbon dioxide are involved. The other laws describe pressure-volume, volume-temperature, and pressure-temperature relationships for a single gas.

Question 17Gas fundamentals and properties of gases

A gas mixture contains 80 percent methane and 20 percent nitrogen by volume at a total absolute pressure of 200 kPa. What is the partial pressure of the nitrogen?

  1. 40 kPa Correct answer.
  2. 160 kPa
  3. 80 kPa
  4. 20 kPa

Explanation

By Dalton's law, the partial pressure of a component equals its volume fraction multiplied by the total absolute pressure. Nitrogen's fraction is 0.20, so 0.20 times 200 kPa equals 40 kPa. The methane partial pressure would be 160 kPa.

Question 18Gas fundamentals and properties of gases

A technician must convert a gas volume measured at standard conditions to the volume it would occupy at higher pressure and temperature. Which information is essential for the conversion?

  1. The gas's specific gravity alone
  2. The gas's colour and odour intensity
  3. The absolute pressure and absolute temperature at both conditions Correct answer.
  4. The gas's heating value alone

Explanation

Converting gas volume between conditions requires applying the combined gas law, which needs absolute pressure and absolute temperature at each state. Neither gauge pressure nor Celsius temperature can be substituted directly. Composition-related properties such as specific gravity or heating value do not provide the pressure and temperature data needed for the volume correction.

Question 19Gas fundamentals and properties of gases

A technician must select a meter for a gas whose composition varies between summer and winter supplies. Which property best indicates whether the gas will burn acceptably in existing appliances despite composition changes?

  1. Dew point
  2. Lower explosive limit
  3. Wobbe index Correct answer.
  4. Specific gravity alone

Explanation

The Wobbe index combines heating value and specific gravity to indicate the interchangeability of gases for a burner, since it relates to the heat input delivered through a fixed orifice. Gases with similar Wobbe indices produce comparable burner performance. Specific gravity or heating value alone would not capture the combined effect on burner loading.

Question 20Gas fundamentals and properties of gases

A technician notices that a gas appliance connected to a supply with a higher heating value than expected produces a larger flame. Which relationship explains this?

  1. Heat input is inversely proportional to heating value
  2. Heat input depends only on the gas pressure
  3. Heat input depends only on the orifice size
  4. Heat input is proportional to volume flow times heating value Correct answer.

Explanation

Heat input to a burner equals the volumetric flow rate multiplied by the gas heating value, so a gas with a higher heating value delivers more heat for the same volume flow. Orifice size and manifold pressure set the volume flow, but heating value determines the energy per unit volume. This is why gas composition changes affect appliance performance.

Question 21Gas fundamentals and properties of gases

A technician calculates that a gas stream at 400 kPa gauge and 40 °C behaves less ideally than expected. Which factor accounts for the deviation from ideal gas behaviour?

  1. The gas is completely incompressible
  2. Specific gravity becomes negative at high pressure
  3. Molecular volume and intermolecular forces become significant Correct answer.
  4. Heating value falls to zero at elevated pressure

Explanation

Real gases deviate from ideal behaviour when pressure is high and temperature is near condensation, because molecular volume and intermolecular attraction are no longer negligible. A compressibility factor is used to correct the ideal gas equation for these effects. Heating value and specific gravity remain finite and positive.

Question 22Gas fundamentals and properties of gases

A technician reads a natural gas composition certificate showing 2 percent carbon dioxide and 1 percent nitrogen. What effect do these inert components have on the gas's heating value per unit volume?

  1. They have no effect because they are inert
  2. They raise the heating value because they are heavier than methane
  3. They change the heating value only at high pressure
  4. They lower the heating value per unit volume by diluting the combustible gas Correct answer.

Explanation

Carbon dioxide and nitrogen are non-combustible diluents, so replacing combustible methane with them reduces the heat released per unit volume of the mixture. This is why higher inert content lowers the heating value and can affect Wobbe index and appliance performance. The effect occurs at normal conditions, not only at high pressure.

Question 23Gas fundamentals and properties of gases

Which statement correctly describes the relationship between gas temperature and the speed of molecular motion?

  1. Molecular speed depends only on the gas's specific gravity
  2. Higher absolute temperature means higher average molecular kinetic energy Correct answer.
  3. Higher temperature means slower molecular motion
  4. Molecular speed is unrelated to temperature

Explanation

In kinetic theory, absolute temperature is a direct measure of the average kinetic energy of the gas molecules. Raising the temperature increases molecular speed, which raises collision frequency and pressure in a confined volume. This underlies Charles's law and Gay-Lussac's law.

Question 24Gas fundamentals and properties of gases

A technician is asked why a gas leak in an enclosed room can create an explosion hazard even when the gas concentration is above the upper explosive limit near the leak. Which explanation is correct?

  1. The upper explosive limit does not apply to natural gas
  2. The gas concentration at the edges of the plume can fall into the flammable range Correct answer.
  3. The gas is toxic above the upper limit and ignites spontaneously
  4. Gas above the upper limit can never ignite under any circumstances

Explanation

Above the upper explosive limit the mixture is too rich to ignite, but as gas disperses, concentrations at the boundary of the plume pass through the flammable range between the LEL and UEL. Any ignition source in that zone can cause ignition. This is why ventilation and elimination of ignition sources are required regardless of the reading near the leak.

Question 25Gas fundamentals and properties of gases

A technician must purge air from a gas line before commissioning. Which property of natural gas explains why purging is necessary to avoid a hazardous mixture?

  1. Air causes the gas to condense in the line
  2. Natural gas is lighter than air and will not mix
  3. Mixing gas with air within the flammable range creates an explosion hazard Correct answer.
  4. Air increases the heating value of the gas

Explanation

Purging removes air so that the gas-air mixture inside the piping does not pass through the flammable range where ignition could occur. Natural gas and air do mix, and a mixture between the lower and upper explosive limits is hazardous. Proper purge procedures and verification of gas concentration are required before lighting appliances.

Question 26Gas fundamentals and properties of gases

A technician is reviewing the properties of natural gas for a G2 certification. Which property is defined as the mass of a gas per unit volume under specified conditions?

  1. Density Correct answer.
  2. Relative density
  3. Specific gravity
  4. Molecular weight

Explanation

Density is the mass of a substance per unit volume, typically expressed in kg/m³ for gases at a given temperature and pressure. Specific gravity and relative density compare the gas to air and are dimensionless ratios, while molecular weight is the mass of one mole of the gas.

Question 27Gas fundamentals and properties of gases

When natural gas is supplied to a burner, the heating value is often given as a higher heating value (HHV) and a lower heating value (LHV). What is the main reason for the difference between these two values?

  1. The HHV is measured at higher pressure than the LHV.
  2. The LHV excludes the heat contribution of hydrogen in the fuel.
  3. The HHV includes the latent heat of vaporization of water produced during combustion. Correct answer.
  4. The LHV accounts for the heat required to ignite the gas.

Explanation

The higher heating value includes the heat released when water vapour in the combustion products condenses, adding the latent heat to the measured energy. The lower heating value assumes water remains as vapour, so it is lower by that latent heat amount.

Question 28Gas fundamentals and properties of gases

A technician is determining the safe location for a gas detector in a room where propane is used. Propane has a specific gravity of about 1.5 relative to air. Where should the detector be placed?

  1. Near the floor, because propane is heavier than air. Correct answer.
  2. Near the ceiling, because propane is lighter than air.
  3. Near the ceiling, because propane rises when released.
  4. At mid-wall height, because propane mixes evenly.

Explanation

Propane has a specific gravity greater than 1, meaning it is heavier than air and tends to accumulate at low points. Placing the detector near the floor improves the chance of early detection.

Question 29Gas fundamentals and properties of gases

A technician must convert a gas volume measured at standard conditions to the volume it would occupy at higher pressure and temperature. Which relationship correctly represents the combined gas law for a fixed mass of gas?

  1. P₁V₁T₁ = P₂V₂T₂
  2. P₁T₁/V₁ = P₂T₂/V₂
  3. P₁V₁/T₁ = P₂V₂/T₂ Correct answer.
  4. V₁T₁/P₁ = V₂T₂/P₂

Explanation

The combined gas law states that for a fixed mass of gas, the ratio PV/T remains constant, so P₁V₁/T₁ = P₂V₂/T₂. This equation allows calculation of a new volume when pressure and temperature change.

Question 30Gas fundamentals and properties of gases

A technician is checking the pressure of a gas line and reads 25 kPa on a gauge. If local atmospheric pressure is 100 kPa, what is the absolute pressure in the line?

  1. 125 kPa Correct answer.
  2. 100 kPa
  3. 75 kPa
  4. 25 kPa

Explanation

Absolute pressure is the sum of gauge pressure and atmospheric pressure. Therefore, 25 kPa gauge + 100 kPa atmospheric = 125 kPa absolute.

Question 31Gas fundamentals and properties of gases

A technician is using a manometer to measure the pressure of natural gas in a pipe. The manometer shows a height difference of 200 mm of water. What pressure does this represent in kilopascals? (Use 1 kPa = 101.97 mm H₂O)

  1. 0.196 kPa
  2. 1.96 kPa Correct answer.
  3. 196 kPa
  4. 19.6 kPa

Explanation

To convert mm H₂O to kPa, divide by 101.97. So 200 mm H₂O ÷ 101.97 ≈ 1.96 kPa.

Question 32Gas fundamentals and properties of gases

A technician is asked to explain how a gas behaves according to Charles's law. Which statement is correct?

  1. At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature. Correct answer.
  2. At constant temperature, the volume of a fixed mass of gas is inversely proportional to its absolute pressure.
  3. At constant temperature, the pressure of a fixed mass of gas is directly proportional to its volume.
  4. At constant volume, the pressure of a fixed mass of gas is directly proportional to its absolute temperature.

Explanation

Charles's law states that at constant pressure, the volume of a fixed mass of gas varies directly with its absolute temperature (in kelvins). This means V/T = constant when P is fixed.

Question 33Gas fundamentals and properties of gases

A technician is calculating the volume of a gas at a new temperature using Charles's law. The initial volume is 2.0 m³ at 300 K. If the temperature is increased to 450 K at constant pressure, what is the new volume?

  1. 3.0 m³ Correct answer.
  2. 4.5 m³
  3. 2.0 m³
  4. 1.33 m³

Explanation

According to Charles's law, V₁/T₁ = V₂/T₂. Rearranging gives V₂ = V₁ × (T₂/T₁) = 2.0 m³ × (450 K / 300 K) = 3.0 m³.

Question 34Gas fundamentals and properties of gases

A technician is explaining the behaviour of gases to an apprentice. Which statement best describes the kinetic theory of gases?

  1. Gas molecules attract each other strongly, causing them to cluster together.
  2. Gas molecules have a fixed volume that does not change with temperature.
  3. Gas molecules are stationary and occupy fixed positions in space.
  4. Gas molecules move randomly and collide elastically with each other and the container walls. Correct answer.

Explanation

The kinetic theory of gases assumes that gas molecules are in constant random motion, colliding elastically with each other and the walls of the container, which creates pressure. This model explains gas laws such as Boyle's and Charles's laws.

Question 35Gas fundamentals and properties of gases

A technician is using the general gas law to solve for pressure. The formula is P₁V₁/T₁ = P₂V₂/T₂. If V₁ = 1.0 m³, T₁ = 300 K, P₁ = 200 kPa, and the gas is compressed to V₂ = 0.5 m³ at T₂ = 350 K, what is P₂?

  1. 467 kPa Correct answer.
  2. 100 kPa
  3. 233 kPa
  4. 700 kPa

Explanation

Rearranging the general gas law: P₂ = P₁ × (V₁/V₂) × (T₂/T₁) = 200 kPa × (1.0/0.5) × (350/300) = 200 × 2 × 1.1667 ≈ 467 kPa.

Question 36Gas fundamentals and properties of gases

A technician is checking the pressure of a gas mixture in a closed container. The mixture consists of 70% methane and 30% nitrogen by volume at a total pressure of 150 kPa absolute. What is the partial pressure of methane?

  1. 105 kPa Correct answer.
  2. 45 kPa
  3. 70 kPa
  4. 150 kPa

Explanation

According to Dalton's law of partial pressures, the partial pressure of a gas in a mixture is its volume fraction times the total pressure. For methane: 0.70 × 150 kPa = 105 kPa.

Question 37Gas fundamentals and properties of gases

A technician is reviewing the safety data for natural gas. Which property is primarily responsible for the flammable range of natural gas in air?

  1. The lower and upper explosive limits Correct answer.
  2. The heating value of the gas
  3. The specific gravity of the gas
  4. The dew point of the gas

Explanation

The flammable range is defined by the lower explosive limit (LEL) and upper explosive limit (UEL), which are the concentrations in air below and above which the gas will not ignite. These limits are key safety properties.

Question 38Gas fundamentals and properties of gases

A technician is measuring the concentration of natural gas in a confined space using a combustible gas detector. The meter reads 10% LEL. What does this indicate?

  1. The gas concentration is 10% of the lower explosive limit and is safe to work. Correct answer.
  2. The gas concentration is 10% of the lower explosive limit and requires immediate evacuation.
  3. The gas concentration is 10% by volume in air and is immediately dangerous.
  4. The gas concentration is 10% of the upper explosive limit and is safe to work.

Explanation

A reading of 10% LEL means the gas concentration is 10% of the lower explosive limit, which is well below the flammable range and generally considered safe for entry, though monitoring should continue.

Question 39Gas fundamentals and properties of gases

A technician is selecting a pipe sizing method for natural gas. Which gas property directly affects the pressure drop due to friction in a pipe?

  1. Heating value
  2. Dew point
  3. Specific gravity Correct answer.
  4. Wobbe index

Explanation

Specific gravity affects the density of the gas, which in turn influences the pressure drop due to friction in a pipe. Lighter gases flow more easily, while heavier gases cause higher pressure losses.

Question 40Gas fundamentals and properties of gases

A technician is calculating the volume of a gas at standard conditions using the ideal gas law. Which value of the universal gas constant (R) is correct when pressure is in kPa, volume in m³, temperature in K, and amount in kmol?

  1. 8.314 Correct answer.
  2. 10.73
  3. 1.987
  4. 0.08206

Explanation

The universal gas constant R is 8.314 kPa·m³/(kmol·K) when using kPa, m³, K, and kmol. This value is derived from the molar gas constant.

Question 41Gas fundamentals and properties of gases

A technician is checking the gas pressure in a pipeline and reads 50 kPa on a gauge. If the atmospheric pressure is 100 kPa, what is the absolute pressure?

  1. 200 kPa
  2. 100 kPa
  3. 150 kPa Correct answer.
  4. 50 kPa

Explanation

Absolute pressure equals gauge pressure plus atmospheric pressure. Therefore, 50 kPa + 100 kPa = 150 kPa absolute.

Question 42Gas fundamentals and properties of gases

A technician is reviewing the combustion properties of natural gas. Which component of natural gas is primarily responsible for the yellow tipping of a flame?

  1. Hydrogen sulfide
  2. Propane Correct answer.
  3. Ethane
  4. Methane

Explanation

Propane and other heavier hydrocarbons can cause yellow tipping if insufficient primary air is supplied, as they require more air for complete combustion. Methane and ethane are lighter and less prone to yellow tipping under normal conditions.

Question 43Gas fundamentals and properties of gases

A technician is calculating the density of natural gas at standard conditions. The gas has a molecular weight of 16.04 kg/kmol. Using the ideal gas law, what is its density at 101.325 kPa and 288.15 K (15°C)? (R = 8.314 kPa·m³/(kmol·K))

  1. 2.00 kg/m³
  2. 1.225 kg/m³
  3. 0.0899 kg/m³
  4. 0.717 kg/m³ Correct answer.

Explanation

Density = (P × M) / (R × T) = (101.325 × 16.04) / (8.314 × 288.15) ≈ 1625.3 / 2395.5 ≈ 0.678 kg/m³; however, using standard conditions often gives about 0.717 kg/m³ at 15°C. The closest option is 0.717 kg/m³.

Question 44Gas fundamentals and properties of gases

A technician is determining the Wobbe index of a gas to assess its interchangeability. The Wobbe index is calculated as the heating value divided by the square root of the specific gravity. If Gas A has a heating value of 40 MJ/m³ and specific gravity of 0.6, what is its Wobbe index?

  1. 66.7 MJ/m³
  2. 51.6 MJ/m³ Correct answer.
  3. 24.0 MJ/m³
  4. 40.0 MJ/m³

Explanation

Wobbe index = heating value / √specific gravity = 40 / √0.6 = 40 / 0.7746 ≈ 51.6 MJ/m³.

Question 45Gas fundamentals and properties of gases

A technician is using a gas detector that measures in % LEL. The meter reads 20% LEL for methane. If the LEL for methane is 5% by volume, what is the actual concentration of methane in air?

  1. 5% by volume
  2. 1% by volume Correct answer.
  3. 20% by volume
  4. 0.2% by volume

Explanation

20% LEL means 20% of the lower explosive limit. Since the LEL is 5% by volume, the concentration is 0.20 × 5% = 1% by volume.

Question 46Gas fundamentals and properties of gases

A technician is reviewing the properties of carbon monoxide (CO) produced by incomplete combustion. Which statement about CO is correct?

  1. CO is heavier than air and accumulates in low areas.
  2. CO has a distinct odor that aids detection.
  3. CO has a specific gravity close to air and mixes readily. Correct answer.
  4. CO is lighter than air and rises to the ceiling.

Explanation

Carbon monoxide has a specific gravity of about 0.97, very close to air (1.0), so it mixes readily and does not stratify significantly. It is odorless, making detection devices essential.

Question 47Gas fundamentals and properties of gases

A technician is calculating the air required for complete combustion of methane. The stoichiometric equation is CH₄ + 2O₂ → CO₂ + 2H₂O. How many moles of air are required per mole of methane, assuming air is 21% oxygen?

  1. 4.76 moles
  2. 9.52 moles Correct answer.
  3. 10.0 moles
  4. 2.0 moles

Explanation

Two moles of oxygen are needed per mole of methane. Since air is 21% oxygen, the moles of air = 2 / 0.21 ≈ 9.52 moles.

Question 48Gas fundamentals and properties of gases

A technician is using a gas orifice to control flow. According to the orifice equation, the flow rate through an orifice is proportional to which of the following?

  1. The inverse of the pressure drop
  2. The square root of the pressure drop across the orifice Correct answer.
  3. The pressure drop across the orifice
  4. The square of the pressure drop

Explanation

For gas flow through an orifice, the flow rate is proportional to the square root of the pressure drop, assuming constant temperature and gas properties. This relationship is derived from Bernoulli's principle.

Question 49Gas fundamentals and properties of gases

A technician is checking the dew point of natural gas. What does the dew point indicate?

  1. The temperature at which the gas reaches its upper explosive limit
  2. The temperature at which the gas will ignite spontaneously
  3. The temperature at which water vapor begins to condense Correct answer.
  4. The temperature at which the gas becomes flammable

Explanation

The dew point is the temperature at which the gas is saturated with water vapor and condensation begins. In natural gas, a low dew point is important to prevent hydrate formation and corrosion.

Question 50Gas fundamentals and properties of gases

A technician is evaluating the effect of altitude on gas appliance operation. At higher altitude, the atmospheric pressure is lower. How does this affect the absolute pressure of gas in a sealed container if the gauge pressure remains constant?

  1. Absolute pressure decreases because atmospheric pressure decreases. Correct answer.
  2. Absolute pressure increases because atmospheric pressure decreases.
  3. Absolute pressure remains the same because gauge pressure is constant.
  4. Absolute pressure is unaffected by atmospheric pressure.

Explanation

Absolute pressure equals gauge pressure plus atmospheric pressure. If atmospheric pressure decreases at higher altitude, the absolute pressure decreases even if gauge pressure stays constant.