Equilibria

Dynamic Equilibrium and Le Chatelier's PrincipleSign up

know that many reactions are readily reversible and that they can reach a state of dynamic equilibrium in which: (i) the rate of the forward reaction is equal to the rate of the backward reaction; (ii) the concentrations of the reactants and the products remain constant · be able to predict and justify the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium in a homogeneous system · evaluate data to explain the necessity, for many industrial processes, to reach a compromise between the yield and the rate of reaction

The Equilibrium Constant KcSign up

Writing the Kc expression for any homogeneous equilibrium · Setting up ICE tables (Initial / Change / Equilibrium) to compute Kc from experimental data · Deriving the units of Kc from Δn and the invariance of Kc under concentration / pressure / catalyst changes

Kp for Gas-Phase EquilibriaSign up

Mole fractions and partial pressures: p_i = x_i × P_total · Building the Kp expression, calculating Kp from equilibrium moles + total pressure, and deriving the units (atm)^Δn

Temperature Effect on K and Extent of ReactionSign up

K depends only on T: concentration, pressure, volume, and catalyst all leave K unchanged · Temperature effect on K for exothermic vs endothermic reactions, linked to ΔS_total = R ln K · Using the magnitude of K (K >> 1, K ≈ 1, K << 1) to predict the extent of reaction

The Haber and Contact ProcessesSign up

describe and explain the conditions used in the Haber process · describe and explain the conditions used in the Contact process · apply Le Chatelier's principle to the yield/rate compromise in industrial equilibria

Bronsted-Lowry Theory, Strong/Weak Acids and pH BasicsSign up

understand that a Brønsted-Lowry acid is a proton donor and a Brønsted-Lowry base is a proton acceptor and that acid-base reactions involve proton transfer · be able to identify Brønsted-Lowry conjugate acid-base pairs · be able to define the term 'pH' · be able to calculate pH from hydrogen ion concentration · be able to calculate the concentration of hydrogen ions in a solution, in mol dm^-3, from its pH, using the expression [H+] = 10^-pH

pH Titration Curves and Indicator SelectionSign up

be able to draw and interpret titration curves, using all combinations of strong and weak monoprotic and diprotic acids with bases, and apply these principles to diprotic acids and bases · be able to select a suitable indicator for a titration, using a titration curve and appropriate data

Conjugate Pairs, Ka, pKa, Kw and pH CalculationsSign up

understand the difference between a strong acid and a weak acid in terms of the degree of dissociation · be able to calculate the pH of a strong acid · be able to deduce the expression for the acid dissociation constant, Ka, for a weak acid · be able to calculate the pH of a weak acid from Ka or pKa values, making relevant assumptions (students will not be expected to solve quadratic equations) · be able to define the ionic product of water, Kw · be able to calculate the pH of a strong base from its concentration, using Kw or pKw · be able to define the terms 'pKa' and 'pKw' · be able to analyse data from the following experiments: (i) measuring the pH of a variety of substances, including equimolar solutions of strong and weak acids, strong and weak bases, and salts; (ii) comparing the pH of a strong and weak acid after dilution 10, 100 and 1000 times · be able to calculate Ka for a weak acid from experimental data given the pH of a solution containing a known mass of acid

Buffer Solutions, Ksp and Partition CoefficientsSign up

know what is meant by the term 'buffer solution' · understand the action of a buffer solution · be able to calculate the pH of a buffer solution given appropriate data · be able to calculate the concentrations of solutions required to prepare a buffer solution of a given pH · understand how to use a weak acid-strong base or strong acid-weak base titration curve to: (i) demonstrate buffer action; (ii) determine Ka from the pH at the point where half the acid is neutralised/equivalence point · understand the importance of buffer solutions in biological environments: (i) buffers in cells and in blood (H2CO3/HCO3-); (ii) in foods to prevent deterioration due to pH change (caused by bacterial or fungal activity) · CORE PRACTICAL 11: Finding the Ka value for a weak acid