LC Physics and Chemistry flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Newton's second law

The net force on an object equals its mass times its acceleration (F = ma). The acceleration is in the same direction as the resultant force.

Conservation of momentum

In a closed system with no external resultant force, total momentum before an interaction equals total momentum after it, including collisions and explosions.

Centripetal force

The net inward force needed to keep an object moving in a circle, of magnitude mv²/r. It is not an extra force but the resultant of real forces.

Specific latent heat

The energy needed to change one kilogram of a substance from one phase to another at constant temperature, without any change in temperature.

Specific heat capacity

The energy required to raise one kilogram of a substance by one kelvin, calculated using Q = mcΔT where Q is energy in joules.

Absolute zero

The lowest possible temperature, 0 K or about −273 °C, at which particles have minimum kinetic energy and gas volume would theoretically reach zero.

Thermal equilibrium

The state reached when two objects in contact have the same temperature, so there is no net transfer of thermal energy between them.

Wave equation

The speed of a wave equals its frequency multiplied by its wavelength (v = fλ). Frequency stays constant when a wave refracts into a new medium.

Total internal reflection

Occurs when light travels from a denser to a less dense medium and the angle of incidence exceeds the critical angle, so all light reflects internally.

Snell's law

Relates angles of incidence and refraction: n₁sinθ₁ = n₂sinθ₂. Light bends toward the normal when entering a medium with a higher refractive index.

Diffraction

The spreading of waves as they pass through a gap or around an obstacle. It is most noticeable when the gap is comparable to the wavelength.

Ohm's law

For an ohmic conductor at constant temperature, current is directly proportional to potential difference, so V = IR and resistance stays constant.

Faraday's law of induction

An emf is induced in a conductor whenever the magnetic flux through it changes; a faster change or more turns gives a larger emf.

Lenz's law

The direction of an induced current always opposes the change producing it, which is a consequence of conservation of energy.

Electrical power

The rate of energy transfer in a circuit, given by P = VI, P = I²R or P = V²/R, measured in watts.

Photoelectric effect

Electrons are emitted from a metal surface when incident light has frequency above a threshold, because photon energy must exceed the work function.

Half-life

The time taken for half the nuclei in a radioactive sample to decay, or for the count rate to halve; it is unaffected by temperature or pressure.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons, so they have different mass numbers.

Ionic bonding

Electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal, giving high melting points and conduction when molten.

Hydrogen bonding

An unusually strong intermolecular attraction between a hydrogen bonded to N, O or F and a lone pair on a nearby electronegative atom.

The mole

The amount of substance containing 6.02 × 10²³ particles, equal to Avogadro's constant, and related to mass by n = m/M.

Limiting reactant

The reactant that is completely used up first and so determines the maximum amount of product formed; other reactants remain in excess.

Percentage yield

The actual mass of product obtained divided by the theoretical maximum mass, multiplied by 100, showing how efficient a reaction is.

pH scale

A logarithmic measure of hydrogen ion concentration, pH = −log[H⁺]; values below 7 are acidic and above 7 are alkaline at 25 °C.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, the position shifts to oppose that change.

Buffer solution

A solution that resists pH change on adding small amounts of acid or base, usually a weak acid mixed with its conjugate base.

Markovnikov's rule

In addition of HBr to an alkene, the hydrogen atom attaches to the carbon already bonded to more hydrogen atoms, giving the major product.

Esterification

The reaction of a carboxylic acid with an alcohol, catalysed by concentrated acid, producing an ester and water; esters have characteristic sweet smells.

Hess's law

The enthalpy change of a reaction is independent of the route taken, so it can be calculated by summing the enthalpy changes of intermediate steps.

Activation energy

The minimum energy colliding particles must have for a reaction to occur; a catalyst lowers it by providing an alternative reaction pathway.

Oxidation and reduction

Oxidation is loss of electrons and an increase in oxidation number; reduction is gain of electrons and a decrease in oxidation number.

Electrolysis

The decomposition of an ionic compound by passing a direct current through it when molten or in aqueous solution, with oxidation at the anode.

Titration technique

A burette delivers a solution of known concentration to a measured volume of another until the indicator changes colour; concordant results are averaged.