EQUILIBRIUM: Given the equation

2 PbS(s) + 3 O2(g) 2 PbO(s) + 2 SO2(g)
What direction will the reaction proceed if additional SO2 was added to the system at equilibrium?

Forward
Reverse
Nothing Happens
Difficult to determine

You really need to do this yourself. LeChatelier's Principle states that a system at equilibrium WILL SHIFT in such a way as to relieve the stress that has been applied. SO, adding SO2 (g) to the system makes the SO2 concentration too large. The reaction, then, will shift so as to remove some of the SO2. Which way must the reaction move in order to DECREASE the SO2? [I realize that "difficult to determine" may be an answer for some students but you know that isn't correct.:-)]

nothing happens

constant

To determine the direction in which the reaction will proceed if additional SO2 is added to the system at equilibrium, you need to analyze the equation and apply LeChatelier's Principle.

LeChatelier's Principle states that when a system at equilibrium is subjected to a change in conditions, the system will shift in a way that minimizes the effect of the change and restores equilibrium.

In this case, adding additional SO2 to the system increases the concentration of SO2. According to LeChatelier's Principle, the reaction will shift in a direction that reduces the concentration of SO2 to relieve the stress caused by the increase.

Looking at the equation, you can see that the forward reaction consumes SO2, while the reverse reaction produces SO2. To decrease the concentration of SO2, the reaction must shift in the forward direction to consume the additional SO2.

Therefore, the correct answer is "Forward" - the reaction will proceed in the forward direction to reduce the concentration of SO2 and restore equilibrium.