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AP Chemistry by Satellite Lectureguide
Student Edition
Chemical Equilibrium
Chapter 14

Objectives

Following your study of this chapter, you should be able to

  1. describe the macroscopic properties which characterize equilibrium reactions.
  2. describe the microscopic properties of equilibrium reactions.
  3. define the term chemical equilibrium.
  4. write the equilibrium expression given a chemical equation which describes an equilibrium reaction.
  5. calculate the magnitude of the equilibrium constant for a chemical reaction.
  6. calculate the concentration of each component in an equilibrium reaction given the initial concentration of each component and the equilibrium constant.
  7. state Le Chatelier's principle and identify the factors which will affect a reaction at equilibrium.
  8. predict the direction a reaction must proceed to establish, or re-establish, equilibrium, under a given set of conditions.
  9. write and use the mathematical equation which relates the equilibrium constant for a chemical reaction to temperature.
  10. describe the difference between an equilibrium constant and a rate constant for a chemical reaction.


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Initially (before any reaction occurs) a 1.00 liter reaction vessel at 25 ºC contains 0.300 moles of NO2 and no nitrogen monoxide or dioxygen. Consider the following:
a) If 0.100 moles of NO2 react, how many moles of NO and O2 are formed? How many moles of NO2, NO, and O2 remain after completion of the reaction?


b) If 0.0873 moles of NO2 react, how many moles of NO and O2 are formed? How many moles of NO2, NO, and O2 remain after completion of the reaction?


c) If '2x' moles of NO2 react, how many moles of NO and O2 are formed (in terms of 'x')? How many moles of NO2, NO, and O2 remain after completion of the reaction?


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1. Complete the equation for each reaction demonstrated in lecture and describe your observations.

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Observations:


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Observations:


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Observations:


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Observations:


Discuss the differences between the completeness of reactions in a) and b) and in reactions c) and d).


2. Complete each of the sections according to the computer experiments performed in lecture.


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2. (Continued)


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For each of the guesses listed in Experiment #7 above, provide an explanation why it may be a reasonable answer or not.


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3. Define the term chemical equilibrium.


4. Write the equilibrium expression, given the following general equation.

IMAGE SCSIMG/SCH1423.gif


Distinguish between the Kp and Kc for the reaction.


5a. Distinguish between the equilibrium constant and the equilibrium constant expression for a chemical reaction.


IMAGE SCSIMG/SCH1424.gif


b. The following reaction is at equilibrium at a particular temperature

IMAGE SCSIMG/SCH1425.gif

and the [H2]eq = 0.012 M, [I2]eq = 0.15 M and [HI]eq = 0.30 M. Calculate the magnitude of Kc for the reaction.


Ans: Kc = 50

c. Using the equilibrium constant calculated in b, calculate the magnitude of the equilibrium constant for the following reactions at the same temperature.

IMAGE SCSIMG/SCH1426.gif


Ans: Kc = 0.02


IMAGE SCSIMG/SCH1427.gif


Ans: Kc = 7.07


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c. The initial concentration of both H2 and I2 is 0.250 M. The reaction occurs as shown below,

IMAGE SCSIMG/SCH1425.gif

When equilibrium is achieved the concentration of HI is 0.393 M. Calculate the magnitude of Kc for the reaction.


Ans: Kc = 53


d. A vessel initially has a partial pressure of NO equal to 0.526 atm and a partial pressure of Br2 equal to 0.329 atm. At equilibrium the partial pressure of Br2 is 0.203 atm. Calculate Kp for the reaction

IMAGE SCSIMG/SCH1430.gif


Ans: Kp = 4.17


IMAGE SCSIMG/SCH1431.gif


Problem Set #24
AP Chemistry by Satellite Name___________________________________


ALL work must be shown in all problems for full credit.


PS24.1. Given the reaction

IMAGE SCSIMG/SCH1432.gif

Initially (before any reaction occurs) a 1.00 liter reaction vessel at 400 ºC contains 0.502 moles of O2 and 0.791 moles of NH3 and no water or nitrogen. Consider the following:

a) If 0.0873 moles of O2 react, how many moles of NH3 must react and how many moles of H2O and N2 are formed? How many moles of O2, NH3, H2O and N2 remain after completion of the reaction?


b) If 0.234 moles of NH3 react, how many moles of O2 must react and how many moles of H2O and N2 are formed? How many moles of O2, NH3, H2O and N2 remain after completion of the reaction?


c) If '3x' moles of O2 react, how many moles of NH3 must react and how many moles of H2O and N2 are formed(in terms of 'x')? How many moles of O2, NH3, H2O and N2 remain after completion of the reaction?


d) If 0.875 moles of H2O are formed, how many moles of N2 are formed and how many moles of O2 and NH3 must react? How many moles of O2, NH3, H2O and N2 remain after completion of the reaction?


IMAGE SCSIMG/SCH1433.gif


PS24.2. Write the equilibrium expression for each of the following chemical equations;

IMAGE SCSIMG/SCH1434.gif


PS24.3. Equilibrium constants for the following reactions have been determined at 550 ºC:

IMAGE SCSIMG/SCH1435.gif

Calculate K (at the same temperature) for the commercially important water gas shift reaction

IMAGE SCSIMG/SCH1436.gif


PS24.4. Calculate Kc for the reaction

IMAGE SCSIMG/SCH1437.gif


if Kc for the reaction

IMAGE SCSIMG/SCH1438.gif

is 1.3 x 104.


IMAGE SCSIMG/SCH1439.gif


PS24.5. A 1.00 liter container initially holds 0.257 moles of NOBr at a given temperature. The reaction which occurs is:

IMAGE SCSIMG/SCH1440.gif

At equilibrium analysis shows 0.240 moles of NO and 0.120 moles of Br2.

a) Which direction did the reaction proceed to establish (reach) equilibrium?


b) How many moles of NOBr reacted in order to form 0.240 moles of NO and 0.120 moles of Br2?


c) How many moles of NOBr remain after equilibrium was established?


d) What is the magnitude of Kc?


PS24.6. In a container, the partial pressure of NOCl is initially 0.340 atm at a given temperature. The reaction which occurs is:

IMAGE SCSIMG/SCH1441.gif

At equilibrium analysis shows the partial pressure of NO is 0.0916 atm.

a) Which direction did the reaction proceed to establish (reach) equilibrium?


b) What is the partial pressure of NOCl which reacted in order for the partial pressure of NO to be 0.0916 atm?


c) What is the partial pressure of Cl2 at equilibrium?


d) What is the partial pressure of NOCl at equilibrium?


e) What is the magnitude of Kp?


IMAGE SCSIMG/SCH1442.gif


PS24.7. A 1.00 liter container holds 1.06 moles of H2 and 1.57 moles of CO at a temperature of 162 ºC. At this temperature, the following reaction occurs,

IMAGE SCSIMG/SCH1443.gif

After equilibrium is established, analysis shows 0.200 moles of CH3OH in the container. Calculate the [CO]eq, [H2]eq and Kc.


PS24.8. The following reaction,

IMAGE SCSIMG/SCH1444.gif

occurs at 298K. If 2.00 mol of HI are placed into a 1.00 liter container and permitted to react, at equilibrium it is found that 20.0 % of the HI has decomposed. Calculate Kc and Kp.


IMAGE SCSIMG/SCH1445.gif


PS24.9 The equation which describes the preparation of ammonia is:

IMAGE SCSIMG/SCH1446.gif

A 3.000 L reaction vessel initially contains 0.3000 moles N2 and 0.4500 moles H2. When the reaction is allowed to attain equilibrium at a given temperature, analysis determines 0.09992 M N2. Calculate Kc for the reaction.


IMAGE SCSIMG/SCH1447.gif


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6a. Setup the ICE table for the following general chemical equation. (Assume the reaction proceeds from left to right to establish equilibrium.)

IMAGE SCSIMG/SCH1449.gif


b. The equilibrium constant, Kp, for the reaction

IMAGE SCSIMG/SCH1450.gif

is 0.0202. If the initial partial pressure of H2 = I2 = 0.350 atm, calculate the equilibrium partial pressures of all species.


Ans: [H2]eq = [I2]eq = 0.327 atm, [HI]eq = 4.64 x 10-2 atm


IMAGE SCSIMG/SCH1451.gif


c. The equilibrium constant, Kc, for the reaction

IMAGE SCSIMG/SCH1452.gif

is 33.3 at 760 ºC. If 0.400 mol of PCl5 are placed in a 2.00 liter container, calculate the equilibrium concentrations of all species.


Ans: [PCl3]eq = [Cl2]eq = 0.195 M, [PCl5]eq = 0.005 M


IMAGE SCSIMG/SCH1453.gif


d. The equilibrium constant, Kc, for the reaction

IMAGE SCSIMG/SCH1454.gif


is 33.3 at 760 ºC. If 0.400 mol of PCl5 and 1.0 mol of Cl2 are placed in a 2.00 liter container, calculate the equilibrium concentrations of all species.


Ans: [PCl3]eq = 0.196 M, [Cl2]eq = 0.70 M, [PCl5]eq = 0.004 M


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7a. State Le Chatelier's principle.


b. Identify three factors which can affect a reaction at equilibrium. Using examples discussed in lecture, briefly describe how each factor can affect a reaction at equilibrium.


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b. (Continued)


c. The reaction

IMAGE SCSIMG/SCH1458.gif

has a DH = -1036 kJ. Given the reaction is at equilibrium, predict the direction the reaction will shift when disrupted by each of the following


i) the amount of H2O is increased


ii) the temperature of the reaction is increased


iii) the volume of the container is decreased


iv) the amount of H2S is decreased


IMAGE SCSIMG/SCH1459.gif


8. Define the non-equilibrium reaction quotient, Q, and explain how it can be used to predict the direction a reaction will proceed to establish equilibrium.


c. The reaction

IMAGE SCSIMG/SCH1460.gif


has been carefully studied at 350 ºC and the Kc is 0.079. Which direction will the reaction proceed to establish equilibrium under each of the following initial conditions?


i) [NOBr]o = 0.100 M : [NO]o = 0 : [Br2]o = 0


ii) [NOBr]o = 0 : [NO]o = 0.100 M : [Br2]o = 0.100 M


IMAGE SCSIMG/SCH1461.gif


iii) [NOBr]o = 0.100 M : [NO]o = 0 : [Br2]o = 0.100 M


iv) [NOBr]o = 0.100 M : [NO]o = 0.100 M : [Br2]o = 0.100 M


v) [NOBr]o = 0.200 M : [NO]o = 0.0500 M : [Br2]o = 0.100 M


IMAGE SCSIMG/SCH1462.gif


IMAGE SCSIMG/SCH1463.gif

9a. Write the general mathematical equation which relates the equilibrium constant for a chemical reaction to temperature.


b. Define each of the variables in this equation.


c. In the reaction

IMAGE SCSIMG/SCH1464.gif


DH = -57.2 kJ at 25 ºC. The equilibrium constant, Kp, at this temperature is 8.8. Calculate Kp at 0 ºC.


Ans: K1 = 72.9


IMAGE SCSIMG/SCH1465.gif


d. In the reaction

IMAGE SCSIMG/SCH1466.gif


DH = 26.9 kJ at 25 ºC. The equilibrium constant, Kc, at this temperature is 4.9 x 10-6. Calculate Kc at 100 ºC.


Ans: K1 = 4.3 x 10-5


10a. Describe the difference between an equilibrium constant and a rate constant for a chemical reaction.


b. How does adding a catalyst to a chemical reaction affect the magnitude of the equilibrium constant for the reaction?


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Problem Set #25
AP Chemistry by Satellite Name___________________________________


ALL work must be shown in all problems for full credit.


PS25.1. A 0.622 gram quantity of COBr2 is sealed in a glass bulb of 0.100 L volume and heated to a temperature of 73 ºC. At 73 ºC the COBr2 partially decomposes according to the equation

IMAGE SCSIMG/SCH1468.gif


for which Kc = 0.190. Calculate the concentration of each species at 73 ºC.


PS25.2. The equilibrium constant, Kp, for the reaction

IMAGE SCSIMG/SCH1469.gif

is 7.31. Calculate the partial pressure of all species at equilibrium for each of the following original mixtures:


a) 1.0 atm of CO and 1.0 atm of H2O.


IMAGE SCSIMG/SCH1470.gif


b) 1.0 atm of CO, 1.0 atm of H2O and 1.00 atm of H2.


c) 1.0 atm of H2 and 1.0 atm of CO2.


IMAGE SCSIMG/SCH1471.gif


PS25.3. At 1000 K the equilibrium constant, Kc, for the reaction

IMAGE SCSIMG/SCH1472.gif

is 0.833. Calculate the concentrations of all species at equilibrium when 0.200 moles of NO2 are placed in a 2.00 L container at 1000 K.


PS25.4. At 25 ºC, 0.560 mol of O2 and 0.20 mol of N2O were placed in a 1.00 liter vessel and allowed to react according to the equation

IMAGE SCSIMG/SCH1473.gif

When the system reached equilibrium, the concentration of NO2 was found to
be 0.020 M.


a) What were the equilibrium concentrations of N2O and O2?


IMAGE SCSIMG/SCH1474.gif


PS25.4. (Continued)


b) What is the value of Kc for this reaction at 25 ºC?


PS25.5. The reaction

IMAGE SCSIMG/SCH1460.gif

has been carefully studied at 350 ºC and the Kc is 0.079. Which direction (left-to-right or right-to-left) will the reaction proceed to establish equilibrium under each of the following initial conditions?

IMAGE SCSIMG/SCH1476.gif

PS25.6. Consider the reaction

IMAGE SCSIMG/SCH1477.gif

for which DHrxn = -1036 kJ. Predict how the [SO2] will change when the equilibrium is disturbed by;

a) Addition of O2
b) Addition of H2O
c) Addition of a catalyst
d) Increase in temperature
e) Decrease in the volume of the reaction container


IMAGE SCSIMG/SCH1478.gif


PS25.7. The equilibrium constant, Kp, for the reaction

IMAGE SCSIMG/SCH1479.gif

is 6.25 at 25 ºC and DHº = 34.4 kJ. Calculate the magnitude of the equilibrium constant at 50 ºC.


PS25.8. Given the reaction

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A 10.0 liter vessel at 298 K initially contains a sample of XeF4 at 0.750 atm. After the reaction achieves equilibrium, the total pressure in the vessel is 1.95 atm. Calculate Kp from this data.


IMAGE SCSIMG/SCH1481.gif


PS25.9. The equilibrium constant, Kc, for the reaction

IMAGE SCSIMG/SCH1482.gif

is 2.50 x 10-6 at a particular temperature. If the [N2]o = 2.00 M, the [O2]o = 1.00 M and the [NO]o = 0 M, calculate the equilibrium concentration of all species.


PS25.4. A 0.383 gram quantity of crystalline PCl5 is sealed in a glass bulb of 0.100 L volume and heated to a temperature of 250 ºC, at which temperature all of the PCl5 has vaporized. At 250 ºC the PCl5 partially decomposes according to the equation

IMAGE SCSIMG/SCH1483.gif

If the [PCl3]eq = 1.4 x 10-2 M, calculate Kc at 250 ºC.


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