### What two things are equal at equilibrium? Summative Problem Equilibrium

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1. What two things are equal at equilibrium?

_ ___ and __ __

2.Consider the following potential energy diagram:

a)Which reaction, forward or reverse, will be affected more by an increase in

``   temperature?________ ___________________``

b)Write a thermochemical equation for the forward reaction using the numerical value

``   for the heat.``

c)When the temperature is first raised, which reaction will increase most in rate, forward

``  or reverse?________ ________________________________``

Explain why._ __

d)If the rate of the forward reaction is faster than the reverse reaction for awhile, what

will happen to the [A2] and [B2]? ____

e)If the [A2] and [B2] increases, what will happen to the rate of the reverse reaction?

f)When the reverse reaction rate catches up to the forward reaction rate, the system is

again at__

g)Since, for awhile, the rate of the forward reaction was faster than the rate of the

reverse reaction, there would be an increase in the concentrations of _____

and a decrease in the concentration of_ ___

in the second equilibrium.

h)We can summarize by saying that the equilibrium has shifted to the _ as

``   a result of increasing the temperature.``

i)Draw a graph showing the rates of the forward and reverse reactions vs. time summarizing what happens in 2(c) to 2(f).

3.Consider the reaction:

A2(g) + B2(g) 2C(g)

a) If one mole of A2 and one mole of B2 are placed in a 1.0 L container, a equilibrium is established in which [A2] and [B2] = 0.40 M and [C] = 1.2 M. If 2.0 moles of C are placed into another 1.0 L container at the same temperature, what will the final concentrations of all the species be? (HINT: This is not a calculation. It deals with how equilibrium can be approached from the left or from the right. )

[A2] = __ [B2] = __ _ [C] = __ _

b)Sketch two graphs showing each of the activities performed in 3a. The graphs are

``  concentration vs. time. ``

(Starting with 1 mole A2 and 1 mole of B2)

(Starting with 2 moles of C)

4.Give four characteristics of the equilibrium state.

1.__ ___

2._ ___

3._ ____

4.__

5.Explain why the colour of NO2 gas first gets darker and then gets lighter when compressed in a syringe. The equation is:

N2O4(g) 2NO2(g)

``                                                  colourless             dark brown        ``

6.Define enthalpy__

7.Define entropy__

8.For the reaction:

ZnCl2(aq) + H2(g) Zn(s) + 2HCl(aq) ?H= +152 kJ

The tendency toward minimum enthalpy favours the ____ . The

tendency toward maximum entropy favours the __

If the reactants are combined will the reaction go to completion, not occur at all or reach a state of equilibrium?

9.For the reaction:

2NaHCO3(s) + heat Na2SO3(s) + CO2(g) + H2O(g)

As this reaction proceeds right, enthalpy is ___creasing and entropy is __creasing.

If the reactants are combined will the reaction go to completion, not occur at all or reach a state of equilibrium?

10.For the reaction:

Cl2(aq) + 25 kJ Cl2(g)

The tendency toward minimum enthalpy favours the ____ . The

tendency toward maximum entropy favours the __

If the reactants are combined will the reaction go to completion, not occur at all or reach a state of equilibrium?

11.For the reaction:

Na(s) + H2O(l) Na+(aq) + OH-(aq) + H2(g) ?H = -184 kJ

Which way will the equilibrium shift when the following changes are made:

b)The pressure is increased ................................____

c)The [OH-] is decreased .....................................____

d)The temperature is decreased .........................____

e)The volume of the container is decreased ........____

12.For the following reaction:

4NH3(g) + 5O2(g) + heat 4NO(g) + 6H2O(g)

Which way will the equilibrium shift (if any) when the following changes are made:

a)[NO] is decreased ............................................__

b)[O2] is increased .............................................__

c)[NH3] is increased ...........................................__

4NH3(g) + 5O2(g) + heat 4NO(g) + 6H2O(g)

d)The temperature is decreased .........................__

e)The volume of the container is increased .........__

f)The total pressure is increased ........................__

g)Helium gas is added to increase the total pressure__

h)The temperature is increased ..........................__

14.In an experiment at 423C, the following concentrations were measured for the equilibrium system:

2HI(g) H2(g) + I2(g)

[HI] = 17.7 x 10-3 M, [H2] = 1.83 x 10-3 M and [I2] = 3.13 x 10-3 M.

Calculate the value for the equilibrium constant (Keq ) at 423C .

15.If, at 423C , the [H2] and [I2] = 4.8 x 10-3 M, calculate the [HI]. Use Keq from

``   question 14.``

16.Given the equilibrium equation:

X2(g) + 3Y2(g) 2XY3(g)

If 2.0 moles of X2 and 2.0 moles of Y2 are added to a 1.0 L container, an equilibrium is established in which the [Y2] = 0.80 M. Find the following at equilibrium. (Use a table.)

[X2] = __ [XY3] = ____ Keq = __

17.The equation: A(g) + B(g) C(g) + D(g) has a Keq = 49 at 25C.

If initially, 1.0 mole of C and 1.0 mole of D are added to a 0.50 L container at 25C, calculate the Trial Keq value. Which way will the reaction shift to reach equilibrium?

18.In the equilibrium in question 17, what, if anything, would happen to the value of the equilibrium constant if the temperature is increased?

19.Write the Keq expression for the following reaction: (Be careful of phases!)

2NaHCO3(s) + heat Na2SO3(s) + CO2(g) + H2O(g)

21.Consider the following equilibrium:

2SO2(g) + O2(g) 2SO3(g) Keq = 6.5 at a certain temperature What will occur when 1.0 mol of SO2, 1.0 mol of O2, and 1.0 mol of SO3 are placed in a 1.0 L container and allowed to reach equilibrium?

a)[SO2] will increase, [SO3] will increase.

b)[SO2] will increase, [SO3] will decrease.

c)[SO2] will decrease, [SO3] will increase.

d)[SO2] will decrease, [SO3] will decrease.

22.Given the equilibrium:

CO(g) + H2O(g) CO2(g) + H2(g) ?H = -41 kJ

Give 5 actions which could cause this equilibrium to shift to the left:

1.

2.

3.

4.

23.How does the addition of a catalyst affect the Keq for a system?

24.Choose the equilibrium which most favours the reactants.

a)NO + 1/2O2 NO2 Keq = 4.4 x 107

b)CO + 1/2O2 CO2Keq = 4.0 x 10-3

c)C + H2O CO + H2Keq = 3.1 x 103

d)NO + H2O NO2 H2Keq = 1.0 x 10-22

25.Consider the following system: 2SO2(g) + O2(g) 2SO3(g) ?H = -99 kJ/mol

What are four things which could be done in order to increase the yield of SO3?

1.

2.

3.

4.

26.Given the equilibrium equation: XY(g) + heat X(g) + Y(g)

If initially, at equilibrium, the [XY] = 3.0 M, the [X] = 5.0 M and the [Y] = 6.0 M, draw a graph showing qualitatively what happens to the concentrations of each species as the following changes are made to the system:

Time I - The temperature is decreased.

Time II - Some X(g) is removed from the system

Time III - Some XY(g) is added to the system

Time IV - The total pressure is increased.

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