M3S7 – Equilibrium

Equilibrium

1 / 10

Which of these systems is NOT in a state of dynamic equilibrium?

A blue Bunsen flame

Ice and water at 273 K

Nitrogen dioxide and dinitrogen tetroxide in a sealed tube

Mercury and mercury vapour in a barometer tube

2 / 10

Each of these statements is true. From which statement is it possible to predict, by application of Le Chatelier's principle that the solubility of sodium hydroxide increases with temperature?

Sodium hydroxide dissolves more rapidly in hot than in cold water.

When sodium hydroxide dissolves in water the process is exothermic

When sodium hydroxide dissolves in its nearly saturated solution the change is endothermic

A saturated solution of sodium hydroxide is in equilibrium with excess solid

3 / 10

When iron(II) chloride solution mixes with silver nitrate solution some silver metal precipitates and the mixture reaches an equilibrium state.

Fe²⁺_(aq) + Ag⁺_(aq) <=> Fe³⁺_(aq) + Ag_(s)

When the aqueous layer is decanted off, the precipitate of silver redissolves on adding a solution of:

iron(II) nitrate

iron(III) chloride

silver nitrate

sodium chloride

4 / 10

Which of these reactions can be reversed by changing the conditions in a typical advanced chemistry laboratory?

(i) CuSO₄.5H₂O_(s) -> CuSO₄_(s) + 5H₂O(l)

(ii) 2Mg_(s) + O₂_(g) -> 2MgO_(s)

(iii) NH₃_(g) + HCl_(g) -> NH₄Cl_(s)

(iv) CH₄_(g) + 2O₂_(g) -> CO₂_(g) + 2H₂O_(l)

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

5 / 10

A small crystal of iodine is dissolved in hexane to give a violet coloured solution. After adding an equal volume of colourless, aqueous potassium iodide and shaking, the system reaches equilibrium with the hexane layer floating on top of the aqueous layer. At equilibrium:

(i) the concentrations of iodine in the two layers are the same

(ii) the iodine in the hexane turns brown

(iii) the iodine molecules stop moving between the two layers

(iv) the concentrations in each layer stop changing

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

6 / 10

Which of these are examples of heterogeneous equilibria?

(i) CaCO₃_(s) <=> CaO_(s) + CO₂_(g)

(ii) Fe²⁺_(aq) + Ag⁺_(aq) <=> Fe³⁺_(aq) + Ag_(s)

(iii) 3Fe_(s) + 4H₂O_(g) <=> Fe₃O₂_(s) + 4H₂_(g)

(iv)Br₂_(aq) + H₂O(l) <=> HOBr_(aq) + H⁺_(aq) + Br^-_(aq)

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

7 / 10

For which of these equilibria does a change in pressure have no effect on the yield of substances on the right-hand side of the equation?

(i) CH₄_(g) + H₂O_(g) <=> 3H₂_(g) + CO_(g)

(ii) 2HI_(g) <=> H₂_(g) + I₂_(g)

(iii) 2SO₂_(g) + O₂_(g) <=> 2SO₃_(g)

(iv) H₂O_(g) + CO_(g) <=> H₂_(g) + CO₂_(g)

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

8 / 10

The reaction of nitrogen with hydrogen to form ammonia is exothermic. Which of these changes increases the proportion of ammonia in an equilibrium mixture of nitrogen, hydrogen and ammonia.

(i) raising the pressure at constant temperature

(ii) raising the temperature at constant pressure

(iii) decreasing the volume at constant temperature

(iv) adding a catalyst

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

9 / 10

The synthesis of sulfur trioxide takes place at 380 ^oC in the presence of a catalyst made from vanadium(V) oxide.

2SO₂_(g) + O₂_(g) <=> 2SO₃_(g) Standard enthalpy change = -297 kJ mol^-1

Reasons for not choosing a lower temperature are that:

(i) the product condenses to a solid at a lower temperature

(ii) the proportion of SO₃_(g) at equilibrium falls if the temperature falls

(iii) the reaction is exothermic

(iv) the catalyst is ineffective at lower temperatures

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

10 / 10

This is the equilibrium in a solution of bromine in water:

Br₂_(aq) + H₂O(l) <=> HOBr_(aq) + H⁺_(aq) + Br^-_(aq)

The orange colour of bromine disappears on adding

(i) sodium bromide

(ii) water

(iii) dilute hydrochloric acid

(iv) sodium hydroxide solution

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

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