Video Transcript
Sulfur trioxide is produced as part
of the process of manufacturing sulfuric acid as shown: two SO2 gas plus O2 gas in
equilibrium with two SO3 gas. △𝐻 for this reaction is negative
196 kilojoules per mole. What effect will adding more oxygen
have on the position of the equilibrium? (A) The equilibrium will not
move. (B) The equilibrium will move to
the right. (C) The equilibrium will move to
the left.
If we want to understand what
effect some change will have on the position of an equilibrium, we should refer to
Le Chatelier’s principle. Le Chatelier’s principle states
that for a dynamic equilibrium, if the conditions change, the position of
equilibrium will move to counteract the change.
In this question, the conditions
that changes is that more oxygen is added. To counteract this change, the
position of equilibrium will move to decrease the amount of oxygen. We’ll use this diagram to help us
visualize this change. We start off with an equilibrium
mixture of the three gases participating in the reaction. When more oxygen is added, the
system is no longer in equilibrium. This also means that more oxygen
gas is available to react with sulfur dioxide. When the excess oxygen gas has
reacted to form more sulfur trioxide, a new equilibrium will be established.
Comparing this new equilibrium
system to the original one, we can see that there are now more products present. So we can say the position of
equilibrium has moved towards the products as a result of adding more oxygen. Since the products are on the
right-hand side of the equation, we’ll often say the position of equilibrium has
moved to the right when the new equilibrium favors the products. So answer choice (B) is the correct
answer to this question. The effect that adding more oxygen
will have on the position of the equilibrium is the equilibrium will move to the
right.
