M5S6 – Equilibria Kc & Kp

Equilibria Kc & Kp

1 / 10

Consider the values of the equilibrium constant for this reversible reaction:

H₂_(g) +I₂_(g) <=> 2HI_(g)

Temperature: 500K, value of K_c = 160

Temperature: 1000K, value of K_c = 54.

This information shows that:

(i) HI decomposes rapidly at 500 K

(ii) Raising the temperature causes the equilibrium to shift to the left

(iii) Raising the pressure causes the equilibrium to shift to the right

(iv) The reaction is exothermic

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

2 / 10

For which of the following equilibria, does raising the pressure favours the formation of products?

(i) H₂_(g) + C_(s) <=> H₂_(g) + CO_(g)

(ii) 4NH₃_(g) + 5O₂_(g) <=> 4NO_(g) + 6H₂O_(g)

(iii) 2HCl_(g) + I₂_(g) <=> 2HI_(g) + Cl₂_(g)

(iv) 2SO₂_(g) + O₂_(g) <=> 2SO₃_(g)

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

3 / 10

These reactions are rapid at 298 K. Which of the reactions goes effectively to completion?

(i) I^-_(aq) + I₂_(aq) <=> I₃^-_(aq) K_c = 7.1 x 10^-² mol^-¹ dm³

(ii) Cu²⁺_(aq) + 4NH₃_(aq) <=> [Cu(NH₃)₄]²⁺_(aq) K_c = 1.4 x 10¹³ mol^-4dm¹²

(iii) 2H₂O_(l) <=> H₃O⁺_(aq) + OH^-_(aq) K_c = 1.0 x 10^-¹⁴ mol² dm^-⁶

(iv) Cu²⁺_(aq) + Zn_(s) <=> Cu_(s) + Zn²⁺_(aq) K_c = 1 x 10³⁷

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

4 / 10

At a given temperature, which of these expressions have a constant value for all equilibrium mixtures of hydrogen, iodine vapour and hydrogen iodide?

(i) [H₂]/[I₂],

(ii) [HI]²/[H₂][I₂],

(iii) [I₂]/[H₂]

(iv) [H₂][I₂]/[HI]²

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

5 / 10

Which of the following are examples of heterogeneous equilibria?

(i) CaCO₃_(s) <=> CaO_(s) + CO₂_(g)

(ii) 2CrO₄²^-_(aq) + 2H⁺_(aq) <=> Cr₂O₇²^-_(aq) + H₂O_(l)

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

(iv) Co²⁺_(aq) + 6NH₃_(aq) <=> [Co(NH₃)₆]²⁺_(aq)

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

6 / 10

K_p = 4 atm for the dissociation of N₂O₄ at 350 K when the equilibrium is described by this equation.

N₂O₄_(g) <=> 2NO₂_(g)

What is the value of K_p for this equilibrium:

2NO₂_(g) <=> N₂O₄_(g)?

0.25 atm-1

4 atm-1

8 atm

16 atm

7 / 10

For the following equilibrium K_c = 25.0 mol^-² dm⁶ at a particular temperature.

CO_(g) + 2H₂_(g) <=> CH₃OH_(g)

Which of these changes of conditions alter the value of K_c?

(i)Raising the concentration of hydrogen

(ii)Adding a catalyst

(iii)Raising the pressure

(iv)Lowering the temperature

(i), (ii) and (iii)

(i) and (iii) only

(ii) and (iv) only

(iv) alone

8 / 10

For the equilibrium: CaCO₃_(s) <=> CaO_(s) + CO₂_(g)

K_c = [CO₂_(g)]

K_c = [CaO_(s)]

K_c = 1/[CO₂_(g)]

K_c = [CaO_(s)][CO₂_(g)]/[CaCO₃_(s)]

9 / 10

If pressures are measured in pascals (Pa) what are the units of K_p for this equilibrium:

2H₂_(g) + O₂_(g) <=> 2H₂O_(g)

Pa

Pa²

Pa^-²

Pa^-¹

10 / 10

A mixture of 1 mol ethanoic acid and 1 mol ethanol was allowed to reach equilibrium at a constant temperature. Analysis of the equilibrium mixture showed that it contained ¹/₃ mol ethanoic acid and ¹/₃ mol ethanol:

CH₃CO₂H_(l) + C₂H₅OH_(l) <=> CH₃CO₂C₂H₅_(l) + H₂O_(l)

What is the value of K_c?

¹/₉

¹/₄

4

9

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