Equilbirum

Which statement is true about a chemical reaction at equilibrium?

• A. The reaction has completely stopped.

• B. The concentrations of the products are equal to the concentrations of the reactants.

• C. The rate of the forward reaction is equal to the rate of the reverse reaction.

• D. The concentrations of the products and reactants are constantly changing.

2. What is the equilibrium constant expression, Kc , for the following reaction? 2NOBr(g) ⇋ 2NO(g) + Br2 (g)

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3. The following are KC values for a reaction, with the same starting conditions, carried out at different temperatures. Which equilibrium mixture has the highest concentration of products?

• A. 1 × 10^-2

• B. 1

• C. 1 × 10^1

• C. 1 × 10^2

What effect will an increase in temperature have on the Kc value and the position of equilibrium in the following reaction?

N2 (g) + 3H2 (g) ⇋ 2NH3 (g) delta(H) = -92kJ

Kc will ________ and the position of equilibrium will shift to _______side.

5. Consider the following equilibrium reaction.

2SO2 (g) + O2 (g) ⇋ 2SO3 (g) delta(H) = -197kJ

Which change in conditions will increase the amount of SO3 present when equilibrium is re-established?

• A. Decreasing the concentration of SO2

• B. Increasing the volume

• C. Decreasing the temperature

• D. Adding a catalyst

6. The Haber process uses an iron catalyst to convert hydrogen gas, H2 (g), and nitrogen gas, N2 (g), to ammonia gas, NH3 (g).

3H2 (g) + N2 (g) ⇋ 2NH3 (g)

Which statements are correct for this equilibrium system?

I. The iron catalyst increases rates of the forward and reverse reactions equally. II. The iron catalyst does not affect the value of the equilibrium constant, Kc . III.The iron catalyst increases the yield for ammonia gas, NH3 (g).

• A. I and II only

• B. I and III only

• C. II and III only

• D. I, II and III

7. The formation of nitric acid, HNO3 (aq), from nitrogen dioxide, NO2 (g), is exothermic and is a reversible reaction.

4NO2 (g) + O2 (g) + 2H2 O(l) ⇋ 4HNO3 (aq)

What is the effect of a catalyst on this reaction?

• A. It increases the yield of nitric acid.

• B. It increases the rate of the forward reaction only

• C. It increases the equilibrium constant.

• D. It has no effect on the equilibrium position.

8. The value of Kc for the reaction H2 (g) + Br2 (g) ⇋ 2HBr(g) is 4.0 × 10^-2 .

What is the value of the equilibrium constant for the reaction

2HBr(g) ⇋ H2 (g) + Br2 (g) at the same temperature?

• A. 4.0 × 10^-2

• B. 2.0 × 10^-1

• C. 25

• D. 400

9. 0.50 mol of I2 (g) and 0.50 mol of Br2 (g) are placed in a closed fask. The following equilibrium is established.

I 2 (g) + Br2 (g) ⇋ 2IBr(g)

The equilibrium mixture contains 0.80 mol of IBr(g).

What is the value of Kc ?

• A. 0.64

• B. 1.3

• C. 2.6

• D. 64

10. A 2.0 dm3 reaction vessel initially contains 4.0 mol of P and 5.0 mol of Q. At equilibrium 3 mol of R is present. What is the value of Kc for the following reaction? P(g) + Q(g) ⇋ R(g) + S(g)

• A. 2/9

• B. 9/20

• C. 4.5

• D. 9