T8 CHEMICAL EQUILIBRIUM_QUESTIONS

CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

CHAPTER 8

CHEMICAL EQUILIBRIUM

Face-to-Face Non Face-to-Face

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At the end of this topic, students should be able to:

8.0 CHEMICAL EQUILIBRIUM

8.1 Dynamic equilibrium (a) Explain a reversible reaction.

(b) State the characteristics of a dynamic equilibrium system
and law of mass action or law of chemical equilibrium.

(c) Interpret the curve of concentration reactants and products
against time for a reversible reaction.

8.2 Equilibrium (a) Define homogeneous and heterogeneous equilibria.
constants, Kc and
Kp (b) Deduce and write expressions for equilibrium constants in
terms of concentration, Kc and partial pressure, Kp for
homogeneous and heterogeneous systems.

Refer to single step reversible reaction only.

(c) Calculate Kc, Kp or quantities of species present at
equilibrium.

(Calculations are limited to problems with quadratic equations
only).

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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

TUTORIAL 8
CHEMICAL EQUILIBRIUM

OBJECTIVE QUESTIONS:

HOUR 6
1. What is a reversible reaction?

A. Chemical reactions which take place in both forward and reverse directions.
B. Chemical reactions which take place in forward direction only.
C. Chemical reactions which take place in reverse direction only.
D. Chemical reactions are those in which reactants and products are present in the same

phase.
(CLO1, C1)

2. Consider the following reaction:

Which of the following statements is TRUE when the system is at equilibrium?

A. Both the forward & reverse reactions have stopped.
B. Neither the forward nor reverse reactions have stopped.
C. The rate of forward reaction is decreased due to the increase in the rate of the reverse

reaction.
D. The sum of the concentrations of P& Q must be equal to the sum of the concentrations

of R & S.
(CLO1, C2)

3. Which of the following reactions is homogeneous system?

A. NH4HS (s) NH3 (g) + H2S (g)

B. CH4 (g) + 2H2O (g) CO2 (g) + 4H2 (g)

C. Fe2O3 (s) + 3CO (g) 2Fe (s) + 3CO2 (g)

D. CaCO3 (s) CaO (s) + CO2 (g)

(CLO1, C2)

4. Choose the correct statement for the reaction

SnCl2 (s) + Cl2 (g) SnCl4 (g)

A.

B.
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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

C.

D (CLO1, C2)
5. Choose the correct equilibrium constant expression, Kc for the reaction

A.
B.
C.
D.

(CLO1, C2)

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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

SUBJECTIVE QUESTIONS:

HOUR 1 (CLO1, C1)
1. (a) Define reversible reaction.

(b) State two characteristics of a dynamic equilibrium.

(CLO1, C1)

2. For the reversible reaction below:

AB

(a) Sketch a graph of the variation of the concentration of A and B with time until the system
has achieved equilibrium.
(CLO1, C2)

(b) Explain the shape of the graph. (CLO1, C2)

3. (a) Define homogeneous and heterogeneous equilibria. (CLO1, C1)

(b) Determine whether the following reactions are homogeneous or heterogeneous.

i. 2PCl3(g) + O2(g ) 2POCl3(g )

ii. FeO (s) + CO (g) Fe(s) + CO2(g)

iii. Ag+(aq) + Fe2+(aq ) Ag(s) + Fe3+(aq )

iv. S(s) + 2 HI (l) H2S(g) + I2(s)

v. 2CO(g) + O2 (g) 2 CO2 (g)

vi. H2 (g) + I2 (g) 2HI(g) (CLO1, C2)

(c) Write the equilibrium law for the above reactions in terms of concentration, Kc and/or

partial pressure, Kp. (CLO1, C2)

4. (a) Consider the reaction,

3O2(g) 2O3(g)

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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

Sketch and label the graph of reactant and product concentrations against time.

(CLO1, C2)

(b) Give the difference between homogenous equilibrium and heterogeneous equilibrium.

(CLO1, C2)

HOUR 2
5. The partial pressures of SO2, O2 and SO3 at equilibrium are 5.05, 2.50 and 101 atm respectively.

Calculate the equilibrium constant, KP for the following reaction.

2SO2 (g) + O2 (g) 2SO3 (g)

(CLO4, C3)

6. The following reaction achieved equilibrium when the partial pressure of bromine gas is 0.60 atm.

FeBr3 (s) FeBr2 (s) + ½ Br2 (g)
Determine Kp.
(CLO4, C3)

7. A 1.00 L container contains an equilibrium mixture of N2O4(g) and NO2(g) at 25oC. The partial
pressures of N2O4 and NO2 in the container are 0.70 atm and 0.50 atm respectively. Calculate
the value of KP at 25OC for the reaction below:

(a) N2O4(g) 2NO2(g)

(b) 2NO2(g) N2O4(g) (CLO4, C3)

8. When water boils in close container an equilibrium is established as follows;

H2O (l) H2O (g)

Calculate the value of Kp for the above equlibrium at 25oC. The vapour pressure of water at 25oC
is 23.8 torr.

(CLO4, C3)

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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

9. Iron reacts with steam to produce hydrogen gas.

3Fe(s) + 4H2O(g) 4H2(g) + Fe3O4(s)

A mixture of iron and steam was allowed to reach equilibrium at 700oC. The equilibrium pressures
of hydrogen and steam are 4.8 kPa and 2.5 atm respectively. Calculate Kp for the reaction.

(CLO4, C3)

10. In a 5-L container, the composition of the mixture at equilibrium is 0.3 mol PCl5, 0.7 mol PCl3 and
0.7 mol Cl2 at temperature 800 C.

PCl5(g) PCl3(g) + Cl2(g)

Determine the equilibrium constant Kc.

(CLO4, C3)

HOUR 3
11. At 25oC, Kp = 7.13 atm–1 for the reaction:

2 NO2(g) N2O4(g)

At equilibrium, the partial pressure of NO2 in a container is 0.15 atm. Calculate the partial

pressure of N2O4 in the mixture. (CLO4, C3)

12. The equilibrium constant, Kp for the following equilibrium is 20.5 atm at 50oC.

A2 (s) + B2X (g) 2AB(g) + X(s)

3.0 mol of A2 is placed in a 10.0 L vessel that contains B2X. At equilibirium, the partial pressure
of B2X gas is 4.5 atm. What is the partial pressure of the AB gas at equilibrium?

(CLO4, C3)

13. The reaction between N2 and O2 at 25oC is represented by the following equation:

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N2(g) + O2(g) 2NO(g) Kp = 1 x 10-25

CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

If the partial pressures of N2 and O2 at equilibrium are 0.75 atm and 0.24 atm respectively,
calculate the partial pressure of NO under this condition.

(CLO4, C3)

14. A reaction is represented by the following equations:

CO3 2-(aq) + H2O(l) OH-(aq) + HCO3 –(aq)

At equilibrium, [OH-] = 0.25 M and [HCO3-] =0.50 M. Calculate the concentration of [CO32-] at
equilibrium if the value of Kc = 0.477.

(CLO4, C3)

15. The equilibrium constant for dissociation of PCl5 gas to form PCl3 gas and Cl2 gas is 0.04 molL-1
at 250oC. The mixture at equilibrium contains 0.2 mol PCl3 gas and 0.12 mol Cl2 gas in a 4.0 L
container at 250oC. Calculate the concentration of PCl5 at equilibrium.

(CLO4, C3)

HOUR 4

16. 0.25 mol of N2 and 0.55 mol of H2 is mixed in a 2.0 L vessel at 300 0C. Calculate the Kc for the
reaction if 0.30 mole of NH3 is formed at equilibrium.
(CLO4, C3)

17. When 1.0 M of acetic acid, CH3COOH and 1.0 M of ethanol, C2H5OH are allowed to achieve

equilibrium at 30oC, 0.67 M of ester, C4H8O2 is produced along with water. Calculate the

equilibrium constant for the reaction. (CLO4, C3)

18. A mixture containing 1.0 mol of A and 0.75 mol of B is placed in a 1.0 L vessel and allowed to
achieve equilibrium. At equilibirium, 0.70 mol of A and 0.60 mol of B remained. Calculate Kc for
the reaction.

2A(aq) + B(aq) C(aq)

(CLO4, C3)
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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)

19. 1.86 mol ammonia is dissolved in 5.0 L of water at 250C according to the following reaction.

NH3(aq) + H2O(l) ⇌ NH4+ (aq) + OH-(aq)

Analysis of the mixture at dynamic equilibrium shows that 0.164 mol of OH- is present. Calculate
Kc. (CLO4, C3)

20. Ammonia, a nitrogen fertiliser, is very soluble in water. It is prepared commercially by the Haber
process according to the following equation :

N2(g) + 3H2(g) 2NH3(g)

In an experiment, 1.0 mol of nitrogen gas and 1.0 mol of hydrogen gas are introduced into a 2.0
dm3 volumetric flask at 450oC. The amount of hydrogen gas at equilibrium is 0.40 mol. Calculate
the equilibrium constant, Kc for the reaction at this temperature.

(CLO4, C3)

HOUR 5
21. The equilibrium constant, Kp for the decomposition of solid ionic compound NH4Cl is 5.98 x 10-9

atm2 at 1200C. The equation of the reaction is as follows;

NH4Cl (s) ⇌ NH3(g) + HCl(g)
Calculate the partial pressure of NH3 and HCl at this temperature.

(CLO4, C3)

22. At 430 C, the equilibrium constant, Kc = 0.54 for the reversible reaction

C6H5 COOH(aq) C6H5 COO-(aq) + H+(aq)

If 4.0 mol of C6H5COOH are initially placed in a 2.0 L container, what is the concentration of the
reactant and products at equilibrium?

(CLO4, C3)

23. Consider the following reaction,

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CHEMISTRY DK014
MATRIKULASI KPM
SISTEM EMPAT SEMESTER (S4S)
2HI (g) ⇌ I2(g) + H2(g)
The equilibrium constant, Kc for the reaction at 400 K is 2.06 x 10-4. In a 1.5 L closed vessel, 3.0
mol of HI was heated to 400K. Calculate the concentrations of HI, I2 and H2 gases in the
container after the reaction reached equilibrium at 400K.

(CLO4, C3)
24. The Kc value for the heterogeneous reaction,

2HCl(g) + I2(s) ⇌ 2HI(g) + Cl2(g)
Is 1.6 x 10-34 at 25oC. An amount of 0.150 mol HCl and solid I2 are placed in 1.00 L container.
Calculate the equilibrium concentration of HI and Cl2 in the container.

(CLO4, C3)

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