10 minutes maximum

An IB Periodic Table is required.

1. Which of the following statements about dynamic equilibrium is not correct?
• A.   All reactants and products are present in an equilibrium mixture.
• B.   The equilibrium state can only be attained from one direction of the reaction.
• C.   The rate of the forward reaction is equal to the rate of the reverse reaction.
• D.   The concentrations of the reactants and the products remain constant.
2. Consider the reaction between H2 and I2 at equilibrium:

H2(g) + I2(g) ⇌ 2HI(g)     ∆H = -13 kJ mol-1,

Which of the following changes will shift the position of equilibrium to the left when applied to the system?

• A.   Increasing the temperature
• B.   Decreasing the temperature
• C.   Increasing the pressure
• D.   Adding more H2(g) and I2(g)
3. In a reversible reaction between A(g) and B(g) to form C(g) and D(g)

aA(g) + bB(g) ⇌ cC(g) + dD(g)

what is the correct expression for its equilibrium constant Kc?

 A. $$K_c = {{c[C] \times d[D]} \over{a[A] \times b[B]}}$$ B. $$K_c = {{[C]^c + [D]^d} \over{[A]^a + [B]^b}}$$ C. $$K_c = {{[C]^c \times [D]^d} \over{[A]^a \times [B]^b}}$$ D. $$K_c = {{[A]^a \times [B]^b} \over{[C]^c \times [D]^d}}$$
4. For the reversible reaction below, what is the effect of adding a catalyst on the position of equilibrium and the value of the equilibrium constant Kc?

CO2(g) + H2(g) ⇌ CO(g) + H2O(g)              ∆H is positive

• A.   The position of equilibrium shifts to the right and Kc increases.
• B.   The position of equilibrium shifts to the left and Kc decreases.
• C.   The position of equilibrium shifts to the right and Kc remains constant.
• D.   The position of equilibrium does not shift and Kc remains constant.

5. Which of the following reactions will have its position of equilibrium shifted to the right when the pressure of the system increases?

 I. 2NO2(g) ⇌ N2O4(g) II. 2BrCl(g) ⇌ Br2(g) + Cl2(g) III. CO2(g) + H2O(l) ⇌ H+(aq) + HCO3- (aq)

• A.   I and II only
• B.   I and III only
• C.   II and III only
• D.   I, II and III
6. Consider the reaction

[Co(H2O)6]2+(aq) + 4Cl-(aq) ⇌ [CoCl4]2-(aq) + 6H2O(l),

the complex ion [Co(H2O)6]2+(aq) is pink in colour and the complex ion [CoCl4]2-(aq) is dark blue. The enthalpy change of the forward reaction is endothermic.

When the reaction is at equilibrium and is subjected to the following changes, which one results in a shift of colour to darker blue? • A.   Increasing the temperature of the reaction mixture
• B.   Decreasing the temperature of the reaction mixture
• C.   Adding more water into the reaction mixture
• D.   Increasing the pressure on the reaction mixture

7. The reaction

2SO2(g) + O2(g) ⇌ 2SO3(g)

has an equilibrium constant Kc at temperature T. What is the equilibrium constant for the reverse reaction

2SO3(g) ⇌ 2SO2(g) + O2(g),

at the same temperature?

• A. √Kc
• B.   ½ Kc
• C.   -Kc
• D.   1/Kc

8. When the reaction

N2(g) + O2(g) ⇌ 2NO(g)

is at equilibrium at 298 K, it has an equilibrium constant K = 4.5 x 10-31.
What is the value for K for the reaction

NO(g) ⇌ ½N2(g) + ½O2(g),

at the same temperature?

• A.   4.5 x 10-31
• B.   6.7 x 10-16
• C.   1.5 x 1015
• D.   2.2 x 1030
9. For the following reaction:

NH3(g) ⇌ ${1}\over{2}$N2(g) + ${3}\over{2}$H2(g)                   ∆H = +46 kJ mol-1

What is the effect of decreasing temperature on the position of equilibrium and the value of the equilibrium constant Kc?

• A.   Position of equilibrium moves to the right and Kc stays the same.
• B.   Position of equilibrium moves to the left and Kc stays the same.
• C.   Position of equilibrium moves to the right and Kc increases.
• D.   Position of equilibrium moves to the left and Kc decreases.
10. For a system at equilibrium, which of the following statements is correct?
• A.   Equilibrium can only be achieved in chemical reactions.
• B.   The reaction quotient Q has the same expression as the equilibrium constant Kc, calculated using non-equilibrium concentrations of reactants and products.
• C.   The higher the value of Kc for a chemical reaction, the more reactants are present at equilibrium.
• D.   A catalyst has no effect on the position of equilibrium, but it increases the value of the equilibrium constant Kc.