SACE Stage 2 Chemistry cheat sheet

Concentration in ppm = (mass of solute ÷ mass of solution) × 10^6; for dilute aqueous solutions, 1 ppm ≈ 1 mg L^-1 because 1 L of water has a mass of about 1.00 kg.

pH = -log10[H3O+] and [H3O+] = 10^-pH; at 25 °C, pH + pOH = 14.

Strong acids and bases ionize completely in water, whereas weak acids and bases only partially ionize and require Ka or Kb equilibrium calculations to determine pH.

Acid deposition decision rule: rainwater with pH below about 5.6 is considered acidified; sulfur dioxide and nitrogen oxides are the primary precursors of sulfuric and nitric acids.

Greenhouse gases absorb infrared radiation emitted by Earth; key examples are carbon dioxide, methane, nitrous oxide, tropospheric ozone and water vapour.

Complete combustion of a hydrocarbon: CxHy + (x + y/4)O2 → xCO2 + (y/2)H2O; incomplete combustion also produces carbon monoxide and soot.

Biochemical oxygen demand measures oxygen consumed by microorganisms decomposing organic matter; a high BOD indicates organic pollution and a risk of dissolved-oxygen depletion.

Instrument calibration requires known standards spanning the expected concentration range, a blank correction, and reading the unknown from the fitted calibration line.

Heavy metals can persist and bioaccumulate in food chains; monitoring may use atomic absorption spectroscopy or inductively coupled plasma techniques.

Reaction rate = change in concentration ÷ time interval; common units are mol L^-1 s^-1, and rate usually decreases as reactants are consumed.

Collision theory: a reaction occurs when particles collide with energy at least equal to the activation energy and with suitable orientation.

For aA + bB ⇌ cC + dD, Kc = ([C]^c[D]^d) ÷ ([A]^a[B]^b) at equilibrium; Kc changes with temperature but not with pressure or concentration.

Reaction quotient Q has the same form as Kc but uses current concentrations; if Q < Kc the forward reaction is favoured, and if Q > Kc the reverse reaction is favoured.

Le Chatelier decision rule: a system at equilibrium shifts to partially oppose changes in concentration, pressure or temperature.

Haber process: N2(g) + 3H2(g) ⇌ 2NH3(g) is exothermic; industrial conditions are about 400–500 °C, 150–250 atm and an iron catalyst.

Contact process: 2SO2(g) + O2(g) ⇌ 2SO3(g) is exothermic; a vanadium(V) oxide catalyst and about 450 °C are used, with high pressure favouring SO3.

A catalyst lowers activation energy by providing an alternative pathway; it increases both forward and reverse rates but does not change equilibrium position or enthalpy change.

Atom economy = (molar mass of desired product ÷ total molar mass of all reactants) × 100%; high atom economy means less waste by mass.

IUPAC suffix priority generally decreases: carboxylic acid > ester > amide > aldehyde > ketone > alcohol > amine > alkene > alkyne.

Common functional groups: alcohol –OH, aldehyde –CHO, ketone C=O, carboxylic acid –COOH, ester –COO–, amine –NH2 and amide –CONH–.

Isomer types: structural isomers differ in connectivity; geometric isomers arise from restricted C=C rotation; optical isomers occur when a chiral carbon has four different groups.

Reaction decision rule: alkenes and alkynes undergo addition; alkanes undergo substitution with halogens under ultraviolet light; alcohols can undergo elimination to alkenes with acid and heat.

Oxidation products: a primary alcohol can form an aldehyde and then a carboxylic acid; a secondary alcohol forms a ketone; tertiary alcohols resist oxidation under normal conditions.

Esterification: carboxylic acid + alcohol ⇌ ester + water, catalysed by concentrated acid; the reaction is reversible and the ester is often separated by distillation.

A peptide bond forms by condensation between the amine group of one amino acid and the carboxyl group of another, releasing water and creating a protein chain.

Denaturation disrupts secondary and tertiary protein structure through heat, pH change or chemicals, usually without breaking peptide bonds, reducing biological function.

Saponification: a triglyceride reacts with sodium hydroxide to produce glycerol and soap, which consists of sodium salts of long-chain fatty acids.

Calorimetry: q = mcΔT, where q is heat energy in joules, m is mass, c is specific heat capacity and ΔT is temperature change.

Enthalpy of combustion is the heat released when one mole of a substance burns completely in oxygen under specified conditions; ΔH is usually negative.

Hess’s law: the overall enthalpy change depends only on initial and final states, so enthalpy changes of individual steps can be added.

Energy density decision rule: a fuel with higher energy released per gram or per litre can deliver more energy for a given mass or volume.

Galvanic cell: oxidation occurs at the anode, reduction occurs at the cathode, and electrons flow through the external circuit from anode to cathode.

Electrolysis uses an external electrical energy source to drive a non-spontaneous redox reaction; oxidation occurs at the anode and reduction at the cathode.

A hydrogen–oxygen fuel cell produces electrical energy and water; it has high efficiency and no carbon dioxide emission at the point of use.

Conventional water treatment may include coagulation, flocculation, sedimentation, filtration and disinfection by chlorination or ultraviolet light.

A resource option is more sustainable when it uses renewable feedstock, has high atom economy, low energy demand and low life-cycle emissions.