Consider the following reaction at equilibrium:

4NH3(g) + 5O2(g) ↔ 4NO(g) + 6H2O(g)
In what direction will the following changes force the reaction?
a) Addition of O2
b) Reduction of the amount of water vapour
c) Increase in the pressure
d) Decrease in the volume
e) If this reaction is exothermic, how does an increase in the temperature influence the
reaction?

In every day language, Le Chatelier's Principle says that an equation in equilibrium will try to undo what we do to it.

Adding O2 means it will shift so as to use up O2. So it goes to the right.
Reducing H2O means it will try to make more H2O so it will shift to the right.

etc.

a) Addition of O2: According to Le Chatelier's principle, when O2 is added, the reaction will shift to the right to counteract the increase in concentration. This means more NO and H2O will be formed.

b) Reduction of the amount of water vapor: Similarly, when the amount of water vapor is reduced, the reaction will shift to the right to produce more water vapor in order to restore equilibrium.

c) Increase in the pressure: If the pressure is increased, the reaction will shift to the side with fewer moles of gas to decrease the pressure. In this case, the reaction will shift to the right since there are a total of 10 moles of gas on the left side (4 moles of NH3 and 5 moles of O2) and 10 moles of gas on the right side (4 moles of NO and 6 moles of H2O).

d) Decrease in the volume: When the volume is decreased, the reaction will shift to the side with fewer moles of gas in order to decrease the pressure. As mentioned earlier, there are a total of 10 moles of gas on both sides of the reaction, so a decrease in volume won't affect the equilibrium position.

e) If this reaction is exothermic, an increase in temperature will favor the reverse reaction in order to absorb the excess heat. This means the reaction will shift to the left to decrease the temperature. Conversely, a decrease in temperature will favor the forward reaction to generate more heat.

To determine the direction in which each change will force the reaction, we need to analyze the Le Chatelier's principle, which states that when a system at equilibrium is subjected to a change, it will reposition itself to counteract the effect of that change and reestablish equilibrium.

a) Addition of O2:
When O2 is added to the system, it will increase the concentration of O2. According to Le Chatelier's principle, the system will shift in the direction that consumes or reduces the excess O2. In this case, the system will shift to the right to produce more NO and H2O, consuming the extra O2 added.

b) Reduction of the amount of water vapor:
If the amount of water vapor is reduced, it means that the concentration of H2O will decrease. According to Le Chatelier's principle, the system will shift in the direction that increases the concentration of the substance that has been reduced. In this case, the system will shift to the left to produce more NH3 and O2, compensating for the decrease in H2O.

c) Increase in pressure:
When the pressure of a gaseous system is increased, it favors the side with fewer moles of gas. In this reaction, the left side has only two moles of gas (4NH3) while the right side has ten moles of gas (4NO + 6H2O). Thus, an increase in pressure would favor the left side. The system will shift to the left, producing more NH3.

d) Decrease in volume:
A decrease in volume will lead to an increase in pressure, and as explained in the previous point, an increase in pressure favors the side with fewer moles of gas. Thus, the system will shift to the left to decrease the pressure by producing more NH3.

e) Increase in temperature (for an exothermic reaction):
When the temperature of an exothermic reaction is increased, the equilibrium position will shift in the direction that consumes heat or reduces temperature. In this case, since the reaction is exothermic (heat is released), the system will shift to the left to consume heat. This means that the production of NH3 will be favored.

It's important to note that these predictions are based on Le Chatelier's principle and assumptions about the reaction. The actual shift may depend on other factors such as reaction kinetics, catalysts, and equilibrium constants.