Unit 1-Chemical Equilibrium

Question 1

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

Answer 1

Equilibrium

Question 2

What is meant by dynamic (or moving) equilibrium?

Answer 2

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

Question 3

The position of the equilibrium can be measured using K.

What is K?

Answer 3

K is the equilibrium constant

Question 4

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 4

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

Question 5

What are the units for the equilibrium constant?

Answer 5

No units

Question 6

What does K > 1 indicate?

Answer 6

The equilibrium lies to the right.

Question 7

Consider the ionisation of ethanoic acid

CH₃COOH + H₂O ⇌ H₃O⁺ + CH₃COO^-

How would the equilibrium constant be expressed?

Answer 7

K = [H₃​O⁺] [CH₃COO^-]​ / [​CH₃COOH​]​

Question 8

CH₃COOH ⇌ H⁺ + CH₃COO^-

If sodium ethanoate solid was added, what would happen to

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

Answer 8

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 9

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

Does equilibrium lie to the left or the right?

Answer 9

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 10

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

Does equilibrium lie to the left or the right?

Answer 10

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 11

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 11

K = [NO₂]²/[NO]²[O₂]

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

= 6.9x10⁵

Question 12

What effect does

1. temperature
2. concentration
3. catalyst

have on K

Answer 12

temperature is the only property which affects K.

If the forward reaction is exothermic, a low temperature will shift the equilibrium right, and K will increase.

If the forward reaction is endothermic, a high temperature will shift the equilibrium right, and K will increase.

concentration and catalyst have NO effect on K