A-Level Objectives for Chemical Equilibria

 7.1 Chemical equilibria: reversible reactions; dynamic equilibrium

a) explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible reaction and dynamic equilibrium

b) state Le Chatelier’s principle and apply it to deduce qualitatively (from appropriate information) the effects of changes in temperature, concentration or pressure on a system at equilibrium

c) state whether changes in temperature, concentration or pressure or the presence of a catalyst affect the value of the equilibrium constant for a reaction

d) deduce expressions for equilibrium constants in terms of concentrations, Kc , and partial pressures, Kp (treatment of the relationship between Kp and Kc is not required)

e) calculate the values of equilibrium constants in terms of concentrations or partial pressures from appropriate data

f) calculate the quantities present at equilibrium, given appropriate data (such calculations will not require the solving of quadratic equations)

g) describe and explain the conditions used in the Haber process and the Contact process, as examples of the importance of an understanding of chemical equilibrium in the chemical industry

 7.2 Ionic equilibria

a) show understanding of, and use, the Br.nsted-Lowry theory of acids and bases, including the use of the acid-I base-I, acid-II base-II concept

b) explain qualitatively the differences in behaviour between strong and weak acids and bases and the pH values of their aqueous solutions in terms of the extent of dissociation

c) explain the terms pH, Ka, pKa and Kw and use them in calculations

d) calculate [H+(aq)] and pH values for strong and weak acids and strong bases

e) explain the choice of suitable indicators for acid-base titrations, given appropriate data

f) describe the changes in pH during acid-base titrations and explain these changes in terms of the strengths of the acids and bases

g) (i) explain how buffer solutions control pH

(ii) describe and explain the uses of buffer solutions, including the role of HCO3 – in controlling pH in blood

h) calculate the pH of buffer solutions, given appropriate data

i) show understanding of, and use, the concept of solubility product, Ksp

j) calculate Ksp from concentrations and vice versa

k) show understanding of the common ion effect

7.3 Partition coefficients

a) state what is meant by partition coefficient; calculate and use a partition coefficient for a system in which the solute is in the same molecular state in the two solvents