Kinetics, equilibria and acids: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Chemistry Topic 5, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
Particles must collide with correct orientation and at least the activation energy. Most collisions are unsuccessful.
Maxwell-Boltzmann distribution
Shows the spread of molecular energies. Raising temperature shifts the peak right and lower, greatly increasing the proportion above activation energy.
Catalyst
Increases rate by providing an alternative route of lower activation energy. Not consumed, and does not shift the equilibrium position.
Rate equation
Relates rate to reactant concentrations raised to their orders. Orders are found experimentally, never from the balanced equation.
Order of reaction
The power to which a concentration is raised in the rate equation. Zero order means the rate is unaffected by that reactant.
Rate-determining step
The slowest step in a mechanism. Only species involved in it, or before it, appear in the rate equation.
Half-life and order
A constant half-life independent of starting concentration is the signature of a first-order reaction.
Arrhenius equation
Links the rate constant to activation energy and temperature. Plotting the log of the rate constant against reciprocal temperature gives a straight line.
Dynamic equilibrium
Forward and reverse reactions continue at equal rates in a closed system, so concentrations stay constant but the reaction has not stopped.
Le Chatelier's principle
If a system at equilibrium is disturbed, the position shifts to oppose the change. Predicts the effect of temperature, pressure and concentration.
Kc
The equilibrium constant in terms of concentration. Changed only by temperature — catalysts and pressure do not alter it.
Kp and partial pressure
The equilibrium constant for gases, using partial pressures. Partial pressure is mole fraction times total pressure.
Brønsted-Lowry acid
A proton donor. A base is a proton acceptor, and every acid has a conjugate base formed after donating its proton.
pH definition
The negative logarithm to base ten of the hydrogen ion concentration in moles per cubic decimetre.
Ka and pKa
The acid dissociation constant measures the extent of dissociation of a weak acid. A lower pKa means a stronger acid.
Buffer solution
Resists pH change on adding small amounts of acid or alkali. Made from a weak acid and its salt, or a weak base and its salt.