Chapter 15 - Chem Quiz

If you were to let the tube on the right sit overnight and then take another picture, would the brown color look darker, lighter, or the same?

The same (once the system reaches equilibrium, the concentrations of NO2 and N2O4 stop changing).

Which of the following variables are equal when the N2O4 (g) <-> 2NO2 (g) reaction reaches equilibrium:

a.) kf and kr

b.) the forward and reverse reaction rates

c.) the concentrations of [N2O4] and [NO2}

b.) the forward and reverse reaction rates

Why does the rate of the forward reaction slow down as the reaction proceeds?

Because the concentration of reactants is decreasing, which reduces the frequency of collisions and hence the rate of the forward reaction.

Is the rate of disappearance of H2 related to the rate of disappearance of N2? If so, how are they related?

Yes. H2 disappears at three times the rate that N2 disappears.

True or False: You can determine if equilibrium has been reached by monitoring the concentration of a single reactant.

True

In which experiment, 3 or 4, does the concentration of N2O4 decrease to reach equilibrium?

Experiment 4

Does the value of Kc depend on the starting concentrations of NO2 and N2O4?

No (if you said yes, it's because you didn't read the chapter)

Is it possible to have a reaction where Kc = Kp? If so, under what conditions would this relationship hold?

Yes, when the number of moles of gaseous products and the number of moles of gaseous reactants are equal.

if the concentration of N2O4 in an equilibrium mixture is .00140M, what is its activity? Assume the solution is ideal.

.00140

What would this figure look like for a reaction in which K ~~ 1?

The boxes would be the same size

For the reaction PCl5 <-> PCl3 + Cl2, the equilibrium constant Kc = 1.1E-2 at 400K. What is the equilibrium constant for the reverse reaction?

1/1.1E-2 (about 91)

How does the magnitude of Kp for the reaction 2HI <-> H2 + I2 change if the equilibrium is written 6H1 <-> 3H2 + 3I2?

It is cubed!

Write the equilibrium-constant expression for the evaporation of water, H2O (l) <-> H2O (g), in terms of partial pressures.

Kp = PH2O

If some of the CO2 (g) were released from the bell jar on the left, the seal then restored and the system allowed to return to equilibrium, would the amount of CaCo3 (s) increase, decrease, or reman the same?

It would decrease. To reesetablish equilibrium, the concentration of CO2(g) would need to return to its previous value. The only way to do that would be for more CaCO3 to decomposed to produce enough CO2(g) to replace what was lost.

At what combination of pressure and temperature should you run the reaction to maximize NH3 yield?

500atm and 400c.

Why does the nitrogen concentration decrease after hydrogen is added?

Nitrogen has to react with the excess hydrogen to make more ammonia and restore equilibrium.

Does the equilibrium 2NC (g) + O2 (g) <-> shift to the right or left if

a.) O2 is added?

b.) NO is removed?

a.) right

b.) left

What happens to the equilibrium 2SO2 (g) + O2 (g) <-> 2SO3 (g) if the volume of the system is increased?

It will shift to the left, the side with a larger number of moles of gas.

Is vaporization an exothermic or endothermic process? Based on Le Chatelier's principle, would you predict the vapor pressure of a gas will increase or decrease as the temperature increases?

Endothermic.

Raising temp. = shifts equilibrium to the right, increasing the vapor pressure of the gaseous product.

Which quantity dictates the speed of a reaction, the energy diff. between initial and transition or diff. between initial and final?

Initial and transition.

If a reaction is carried out in the presence of a catalyst, will the amount of product at equilibrium increase, decrease, or stay the same?

Stay the same

Estimate the value of Kp at 1200K, the exhaust gas temp.

5x10^-4