Unit 2 Chemical Equilibrium

Question 1

Higher recap

What happens when a system at equilibrium is subjected to a change?

Answer 1

The system will adjust itself to counteract the applied change.

Le Chatelier’s principle

Question 2

The point when the rates of the forward and reverse reactions in a reversible reaction are equal is known as?

Answer 2

Equilibrium

Question 3

What is meant by dynamic (or moving) equilibrium?

Answer 3

At equilibrium the forward and reverse reactions still continue, but at the same rate.

Question 4

If [reactants]>[products], the position of equilibrium is said to lie to which side?

Answer 4

Left-hand side

Question 5

If [products]>[reactants], the position equilibrium is said to lie to which side?

Answer 5

Right-hand side

Question 6

The position of the equilibrium can be measured using K.

What is K?

Answer 6

K is the equilibrium constant

Question 7

Consider the reaction represented by the equation

aA + bB ⇌ cC + dD

where A and B are reactants, C and D are products and a, b, c and d are the stoichiometric coefficients in a balanced reaction equation.
In terms of concentration, the equilibrium constant can be expressed as?

Answer 7

K = [C]^c[D]^d/[A]^{<span>a</span>}[B]^b

Question 8

What are the units for the equilibrium constant?

Answer 8

No units

Question 9

Consider the ionisation of ethanoic acid

CH₃COOH ⇌ H⁺ + CH₃COO^-

How would the equilibrium constant be expressed?

Answer 9

K = [H⁺] [CH₃COO^-]​ / [​CH₃COOH​]​

Question 10

CH₃COOH ⇌ H⁺ + CH₃COO^-

If sodium ethanoate solid was added, what would happen to

1) the position of equilibrium?
2) the pH?

Answer 10

1) Equilibrium would shift to the left
2) pH would increase

This is because of a reaction between H⁺(aq) and CH₃COO^-(aq) ions to make CH₃COOH(aq)

Question 11

The dissociation of ethanoic acid has an equilibrium constant of 1.7x10^-5

Does equilibrium lie to the left or the right?

Answer 11

Calculating the equilibrium constant is done by the products divided by the reactants. A constant less than 1 must means more reactants than product, therefore equilibrium to the left.

Question 12

The conversion of ozone to oxygen has an equilibrium constant of 1x10⁵⁵

Does equilibrium lie to the left or the right?

Answer 12

Calculating the equilibrium constant is done by the products divided by the reactants.

A number larger than 1 must mean more products than reactants, therefore, equilibrium to the right.

Question 13

The decomposition of hydrofluoric acid has an equilibrium constant of 1x10^-13

Does equilibrium lie to the left or the right?

Answer 13

Calculating the equilibrium constant is done by the products divided by the reactants. A number smaller than 1 must mean more reactants than products, therefore, equilibrium to the left.

Question 14

An equilibrium mixture of gaseous O₂, NO and NO₂ at 500 K contains 1.0 x 10^_-3 moll^-1 O₂, 1.9 x 10^-3 moll^-1 NO and 5.0 x 10^-2 moll^-1 NO₂. Calculate the value of K.

O₂ + 2NO ⇌ 2NO₂

Answer 14

K = [NO₂]²/[NO]²[O₂]

K = (5.0x10^-2)² / (1.9x10^-3)² (1.0x10^-3)

= 6.9x10⁵