AP Chemistry - Equilibrium Worksheet #3
Equilibrium Review
1.  Two colourless solutions are mixed in a stoppered flask. As the reaction proceeds, the resulting solution turns red, and a colourless gas is formed. After a few minutes, no more gas is evolved but the red colour remains. What evidence is there that equilibrium has been established? 
 
2. At a given temperature, analysis of an equilibrium mixture represent below is given as: 

SO2(g) + NO2(g) <=====> SO3(g) + NO(g)    where

[SO2] = 4.0 M, [NO2] = 0.50 M, [SO3] = 3.0 M, [NO] = 2.0 M   Find the value of Keq
 
3. For each of these reactions, indicate the property which might be observed in order to determine when equilibrium has been reached. 

a) PCl5(g) <====> PCl3(g) + Cl2(g)

b) CaCO3(s) <=====> CaO(s) + CO2(g)

c) H2O(l) <====>  H2O(g) 

d) Cl2(g) + 2 H2(g) <====> H2(g) + 2 HCl(g) 

e) 2 HBr(g) <====> H2(g) + Br2(g) 
 
4. Consider the reaction:    N2O4(g)  <=====> 2 NO2(g)

delta Ho = 58.576 kJ; Keq = 0.87 at 55o

What is the effect of each of these changes upon the concentration of N2O4 at equilibrium? 

a)   increasing the temperature, 

b)   increasing the volume, 

c)   adding more NO2(g) to the system without changing pressure or temperature, 

d)   adding He gas to the container, 

e)   adding a catalyst. 
 
5.  How can you increase the concentration of the product(s) in each of these reactions by varying the temperature and pressure (caused by volume change)? 

(a) 4 NH3(g) + 5 O2(g) <=====>  4 NO(g) + 6 H2O(g)   delta Ho = -903.75 kJ 

(b) Br2(g) + Cl2(g) <=====>  2 BrCl(g)                  delta Ho = 14.64 kJ 

(c) BaSO4(s)  <=====> Ba2+(aq) + SO42-           delta Ho = 24267.2 kJ 
 
6. Does the equilibrium constant for the reaction 

Br2(l) <======>  Br2(g) 

increase or decrease as temperature increases? Explain. 
 
7. A substance (CD) decomposes into C and D. 

CD(g) <======> C(g) + D(g) 

At the temperature of the experiment, 15.0 percent of CD is decomposed when equilibrium is established. 

a)   If the initial concentration of CD is 0.200 mol/L, what are the equilibrium concentrations of CD, C and D? 

b)   What is K for the reaction at this temperature? 
 
8.  A reaction may be represented by:      A(g) + B(g) <=====> AB(g) 

At a given temperature 1.0 mole of A and 1.0 mole of B are placed in the 1.0 litre vessel and allowed to reach equilibrium. Analysis revealed that the equilibrium concentration of AB was 0.40 molar. What percent of A had been converted to products? 
 
9. Gas X2 reacts with gas Y2 according to the equation:   X2 + Y2 <=====> 2 XY 

0.50 mole each of X2 and Y2 are placed in a 1.0 litre vessel and allowed to reach equilibrium at a given temperature. The equilibrium concentration of XY is found to be 0.025 mol/L. What is the equilibrium constant for this reaction? 
 
10.  Under a given set of conditions, an equilibrium mixture 

SO2(g) + NO2 <=====> SO3(g) + NO(g) 

in a 1.00 L container was analyzed and found to contain 0.300 mole of SO3, 0.200 mole of NO, 0.0500 mole of NO2, and 0.400 mole of SO2. Calculate the equilibrium constant for this reaction.
 
11. At 55oC, the K for the reaction:  2 NO2(g) <=====> N2O4(g)   is 1.15

a)   Write the equilibrium expression. 

b)   Calculate the concentration of N2O4(g) present in equilibrium with 0.50 mole of NO2
 
12.  One mole of NH3 was injected into a 1 L flask at a certain temperature. The equilibrium mixture 

2 NH3 <=====> N2 + 3 H2

was then analyzed and found to contain 0.300 moles of H2.

a) Calculate the concentration of N2 at equilibrium. 

b) Calculate the concentration of NH3 at equilibrium. 

c) Calculate the equilibrium constant for this system at this temperature and pressure. 

d) Which way would the equilibrium be shifted if 0.600 mole of H2(g) were injected into the flask? 

e) How would the injection of hydrogen into the flask affect the equilibrium constant? 

f) How would the equilibrium constant be affected if the pressure of this system were suddenly increased? 
 
13. When 0.5 mole of CO2 and 0.5 mole of H2 were forced into a 1 litre reaction container, and equilibrium was established:

CO2(g) + H2(g) <======> H2O(g) + CO(g) 

Under the conditions of the experiment, K=2.00. 

a) Find the equilibrium concentration of each reactant and product.

b) How would the equilibrium concentrations differ if 0.50 mole of H2O and 0.50 mole of CO had been introduced into the reaction vessel instead of the CO2 and H2
 
14. At 462oC, the reaction 

(1) heat + 2 NOCl(g) <=====> 2 NO(g) + Cl2(g)

has an equilibrium constant, Keq = 8.0 x 10-2

a) What is Keq at 462oC for the reaction 

2 NO(g) + Cl2(g) <=====> 2 NOCl(g) 

b) What is Keq at 462oC for the reaction 

NOCl(g) <=====> NO(g) + ½Cl2(g) 

Answer these true-or-false questions related the reaction (1) at 462oC.

c) ______ The reaction is exothermic 

d) ______ After equilibrium is established, increasing the concentration of NO causes an increase in the concentration of Cl2

e) ______ After equilibrium is established, decreasing the volume of the container favours the formation of NOCl. 

f) ______ After equilibrium is established, increasing the temperature favours the formation of NO and Cl2

g) ______ After equilibrium is established, decreasing the partial pressure of Cl2 causes the equilibrium position to shift to the left.

h) ______ Adding argon gas to the equilibrium system at constant total pressure will cause an increase in the yield of products. 

i) ______ Adding a catalyst decreases the time required for the reaction to reach equilibrium. 

j) ______ Adding more NOCl to the equilibrium system changes the value of Keq.

k) ______ Increasing the temperature causes Keq to increase. 

l) ______ Adding a catalyst causes Keq to change. 

m) ______ The addition of a catalyst increases the yield of product. 

n) ______ At 462oC, two moles of NOCl react completely and form 3 moles of product (2 moles of NO and 1 mole of Cl2.) 

o) ______ Increasing the temperature increases the rate of the forward reaction. 

p) ______ Increasing the temperature increases the rate of the reverse reaction. 

q) ______ At a given temperature only one set of product and reactant concentrations satisfies Keq