1000 Questions Equilibria

Equilibria

Question 1

A mixture of 2 mole of A and 1 mole of B was allowed to reach equilibrium in a 1L vessel according to the following equation:

$3A_{(l)}+2B_{(l)}\rightleftharpoons C_{(l)}+2D_{(l)}$

The equilibrium mixture was found to contain 0.4 moles of B.

Calculate the value for K_c of this reaction.

Answer:0.507mol^-2 dm⁶(Working)

Question 2

7.43g of SO₂Cl₂ was put in a 2dm³ sealed vessel.

At equilibrium the contained 0.0345mol of Cl₂. Calculate the equilibirum constant for the reaction:

$SO_2Cl_{2(g)}\rightleftharpoons SO_{2(g)}+Cl_{2(g)}$

Answer: 0.597mol dm^-3(Working)

Question 3

The following equilibria was found to contain 3 moles of HI, 6 moles of H₂ and 1 mole of I₂.

$2HI_{(g)}\rightleftharpoons H_{2(g)}+I_{2(g)}$ Find k_c.

Answer: 1.5 (Working)

Question 4

The following equilibria was found to contain 3 moles of NO₂ and 6.7 moles of N₂O₄. The
total pressure of the sealed vessel was 101350Pa.

$N_2O_{4(g)} \rightleftharpoons 2NO_{2(g)}$

Calculate Kp.

Question 5

The following equilibria was established. It has a Kp of 7.48 × 10^–8 kPa^–2. The mixture has a total pressure of 5MPa. The partial pressures of H₂ and NH₃ are 2814 and 1250 respectively.

$N_{2(g)} + 3H_{2(g)}\rightleftharpoons 2NH_{3(g)}$

Calculate the mole fraction of N2

Question 6

9.20 g of N₂O_4(g) was heated to a temperature of 340 K at a pressure of 13.3 kPa.

$N_2O_{4(g)} \rightleftharpoons 2NO_{2(g)}$

Once equilibrium had been reached, 70% of the N₂O_4(g) had dissociated.
Use this information to calculate Kp

Question 7

The following equilibrium was established in a 2dm³ vessel at a particular temperature. 0.20 moles of H₂ was mixed with an unknown amount of I₂. At equilibrium 0.24 moles of HI were made.

$H_{2(g)} + I_{2(g)} \rightleftharpoons 2HI{(g)}$

If K_c = 10.00 calculate the number of moles of Iodine present at the start.

Question 8

Consider the following equilibria:

$2SO_{2(g)} + O_{2(g)}\rightleftharpoons 2SO_{3(g)} \Delta H =-197 kJ mol^{-1}$
a) Explain what happens to the equilibria and the value of K_c if the temperature is increased?
b) Explain what happens to the equilibria and the value of K_c if more SO₂ is added?
c) Explain what happens to the equilibria and the value of K_c if the pressure id doubled?
d) Explain what happens to the equilibria and the value of K_c if a catalyst is added?

Question 9

In a different reaction, Catherine wants to make butyl ethanoate. She reacts butanol with ethanoic acid in 50 cm³of water in a round bottomed flask.

$C_4H_9OH_{(l)} + CH_3COOH_{(l)} \rightleftharpoons CH_3COOC_4H_{9(l)} + H_2O_{(l)}$

She wishes to make exactly 0.25 mol of butyl ethanoate. If she starts with 0.5 mol of ethanoic acid, how much butanol should she add? (Kc for the equilibrium at 20^oC is 3.0. The density of water is 1 g cm^–3)

Question 10

N₂O₄_(l) is an important component of rocket fuel. Equilibrium is established in the reaction

$N_2O_{4(g)}\rightleftharpoons 2NO_{2(g)}$

Given: 3.00 L container, 8.31 g N₂O₄, 1.82 g NO₂

What is the K_c for this reaction?

Question 11

51g of CH₃COOCH₂CH₃ was mixed with 36g of water containing some HCl as a catalyst for the hydrolysis reaction. When the equilibrium was reached the solution was made up to 250cm³ and a 25 cm³ sample was titrated against 1 mol dm^-3 NaOH solution.

The ethanoic acid formed required 29.5 cm³ of NaOH solution for complete neutralisation. Find K_c for the reaction:

$CH_3COOCH_2CH_{3(l)}\rightleftharpoons CH_3COOH_{(l)}+CH_3CH_2OH_{(l)}$

Question 12

The two common chlorides of Phosphorus, PCl₃ and PCl₅, both important in the production of other phosphorous compounds, coexist in equilibrium through:

$PCl_{3 (g)} + Cl_{2 (g)} \rightleftharpoons PCl_{5 (g)}$

At 250 ^oC, an equilibrium mixture in a 2.50 L flask contains 0.105 g PCl₅, 0.220 g PCl₃, and 2.12 g Cl₂. What are the values of (a) Kc and (b) Kp for this reaction?

Question 13

Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

$CH_3COOH_{(l)}+C_2CH_5OH_{(l)}\rightleftharpoons CH_3COOC_2H_{5(l)}+H_2O_{(l)}$

i) At 293K, if one starts with 1.5 mol of acetic acid and 0.27 moles of ethanol, there is 0.213 moles of ethyl acetate at equilibrium. Calculate K_c.

ii) Starting with 0.6 mol of ethanol and 1.0 mol of acetic acid at temperature of 293K, 0.227 mol of water were noted at equilibrium. Has equilibrium been reached?

Question 14

K_p for a reaction is 0.04 atm at 899K for the equilibrium shown below:

$2A_{(g)}+2B_{(g)}\rightleftharpoons C_{(g)}+3D_{(g)}$

What is the equilibrium concentration of A if the initial concentrations of A and B were 4.0 atm each?

Question 15

FeO can be reduced by CO to form Fe and CO₂as seen in the following equation:

$FeO_{(s)}+CO_{(g)}\rightleftharpoons Fe_{(s)}+CO_{2(g)}$

What are the equilibrium partial pressures of CO and CO₂ at 1050K if the initial partial pressures are 1.4 and 0.8atm respectively and K_p = 0.265?

Question 16

The K_p for the following reaction is 1.6 x 10⁵ at 1024K:

$H_{2(g)}+Br_{2(g)}\rightleftharpoons 2HBr_{(g)}$

Find the equilibrium pressures of all gases if 10 bar of HBr was introduced into a sealed container.

Question 17

The water-gas shift reaction is important in several chemical processes, such as the production of H₂ for fuel cells. This reaction can be written as follows:

$H_{2(g)}+CO_{2(g)}\rightleftharpoons H_2O_{(g)}+CO_{(g)}$

K = 0.106 at 700 K. If a mixture of gases that initially contains 0.0150 M H₂ and 0.0150 M CO₂ is allowed to equilibrate at 700 K, what are the final concentrations of all substances present?

Harder Questions

Question 18

A sealed flask containing gases A and B in the mole ratio 1:3 was maintained at 750 K until equilibrium was established:

$A_{(g)}+3B_{(g)}\rightleftharpoons 2C_{(g)}$

The partial pressure of C in teh equilibirum mixture was 6 atm when the total pressure was 22 atm. Find K_p.

Question 19

1.4 moles of SO_3(g) are placed into a 4.70 dm³ container and heated to 1105 K.

$2SO_{3(g)} \rightleftharpoons 2SO_{2(g)} + O_{2(g)}$

• The total pressure of the equilibrium mixture is 3.45 × 10⁶ Pa.
• Use this information to calculate Kp

Hint: Use PV=nRT to find total moles at equilibrium.

Question 20

$2NO_2\rightleftharpoons 2NO + O_2$

NO₂ is dissociated to the extent of 56.6% @ 494 ^oC 99kPa. At what pressure will the dissociation be 80% @ 494 ^oC?

Hint: Find K_p when there is 56.6% dissociation first.

Question 9

Sulfur dichloride dioxide has an apparent molecular mass of 96.5g mol^-1 at 400^oC and a pressure of 1atm. Calculate the equilibrium constant k_c of the reaction at this temperature.

$\dpi{100} SO_2Cl_2\rightleftharpoons SO_2+Cl_2$

Answer:0.026mol dm^-3(Working)

Question 10

In the equilibrium:

$\dpi{100} N_2O_4\rightleftharpoons 2NO_2$

2.50g of dinitrogen tetroxide occupy a volume of 1.00dm³ at 1atm and 25^oC. Calculate: a) the degree of dissociation, and b) the equilibrium constant

Answer: 0.0549 mol dm^-3(Working)