Chemistry 30

For each of the following equilibria, predict whether the system will shift in the forward or reverse directions. Note the energy changes involved and assume that the volume remains constant.

a.	heat is removed from: A B	ΔH° = +40.0 kJ
	Answer: Removing heat favors the exothermic direction to replace the lost heat. Thus the reverse direction will be favored.
b.	heat is removed from: A + B 2 C	ΔH° = -25.5 kJ
	Answer: In this case the forward direction is the exothermic direction, so the forward reaction is favored.
c.	heat is added to: A + 2B 3 C	ΔH° = -32.0 kJ
	Answer: The reverse reaction is endothermic, so it will be favored to remove the excess heat.

In each of the following equilibria, would you increase or decrease the temperature to force the reaction in the forward direction?

a.	H2 (g) + CO2 (g) H2O(g) + CO(g)	ΔH° = +41.0 kJ
	Answer: Increase temperature, because the forward direction is endothermic and will use up the additional heat.
b.	2 SO2 (g) + O2 (g) 2 SO3 (g)	ΔH° = -198 kJ
	Answer: Decrease, because the forward reaction will produce heat removed by making the system cooler.

For each of the equilibria in Question 2 will the value for K_eq increase or decrease if the temperature is raised?

Explain the effect of using a platinum catalyst in the equilibrium reaction of ammonia with oxygen:

4 NH_{3 (g)} + 5 O_{2 (g)} 4 NO_(g) + 6 H₂O_(g) + heat

Answer:

The addition of a catalyst will cause the system to reach equilibrium sooner, but it will have no effect on equilibrium once it has been reached.