If More Dinitrogen Tetroxide Is Added, How Will the Equilibrium Be Affected?

Chem 2 AP

UNIT 10 WORKSHEET #2 – Le Chatelier

1. For the reaction system: N2O4(g) D 2 NO2(g); where the N2O4 is colorless and the NO2 is reddish brown, the color becomes a darker red with an increase in temperature. Is the reaction endothermic or exothermic? Explain. Is heat a ‘product’ or ‘reactant’?

If more dinitrogen tetroxide is added, how will the equilibrium be affected?

If more nitrogen dioxide is added, how will the equilibrium be affected?

2. Consider H2, I2, and HI all in a 1.00 dm3 container at 425 0C with Kc = 55.5. The following equilibrium concentrations are present: [H2] = [I2] = 2.12 x 10-3 and [HI] = 1.58 x 10-2. To this system an additional 0.0480 mol of HI is added. Calculate the new concentrations that will be present when the system reaches equilibrium.

3. Consider the reaction to produce ammonia. At such a temperature that Kc = 1.00 and that each species has a concentration of 1.0 M, write the equilibrium expression and substitute into the expression the molar concentrations of the reactants and product.

Now, decrease the size of the reaction vessel by ½ and at that ‘instant’ calculate the reaction quotient. What way must the system shift in order to establish equilibrium? Does an application of Le Chatelier’s principle give the same answer?

4. For the system 2 NOBr(g) D 2 NO(g) + Br2(g) + 344 kJ, Kp = 0.16 at 25 0C. Predict and explain the effect of each of the following changes on the equilibrium position; that is will it shift left, right, or no change?

a. adding more NO(g)

b. adding more NOBr(g)

c. Decrease the volume of the reaction chamber

d. increase the temperature

5. NH4HS(s) « NH3(g) + H2S(g) DHº = +93 kilojoules

The equilibrium above is established by placing solid NH4HS in an evacuated container at 25ºC.

At equilibrium, some solid NH4HS remains in the container. Predict and explain each of the

following.

(a) The effect on the equilibrium partial pressure of NH3 gas when additional solid NH4HS is introduced into the container

(b) The effect on the equilibrium partial pressure of NH3 gas when additional solid H2S is

introduced into the container

(d) The effect on the mass of solid NH4HS present when the temperature is increased.

6. C(s) + H2O(g) « CO(g) + H2(g) DHº = +131kJ

A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g), and H2(g) at equilibrium. State whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance. Explain each answer with a short statement.

(a) Additional H2(g) is added to the equilibrium mixture at constant volume.

(b) The temperature of the equilibrium mixture is increased at constant volume.

(d) The graphite pellets are pulverized.

7. SO2Cl2(g) D SO2(g) + Cl2(g)

A 4.32 g sample of liquid SO2Cl2 is placed in a rigid, evacuated 1.50 L reaction vessel. As the

container is heated to 400. K, the sample vaporizes completely and starts to decompose according to the

equation above. The decomposition reaction is endothermic.

(a) If no decomposition occurred, what would be the pressure, in atm, of the SO2Cl2(g) in the vessel at

400. K ?

(b) When the system has reached equilibrium at 400. K, the total pressure in the container is 1.26 atm.

Calculate the partial pressures, in atm, of SO2Cl2(g) , SO2(g) , and Cl2(g) in the container at 400. K.

(i) write the equilibrium-constant expression for Kp for the reaction, and

(ii) calculate the value of the equilibrium constant, Kp .

(d) The temperature of the equilibrium mixture is increased to 425 K. Will the value of Kp increase,

decrease, or remain the same? Justify your prediction.

(e) In another experiment, the original partial pressures of SO2Cl2(g) , SO2(g) , and Cl2(g) are 1.0 atm

each at 400. K. Predict whether the amount of SO2Cl2(g) in the container will increase, decrease, or

remain the same. Justify your prediction.