Consider the reaction N2(g)+3H2<-->2NH3(g). What is the effect of decreasing the volume on the contained gases

The reaction shifts toward the product gas

The system reacts by increasing the number of gas molecules***

the pressure on the gases decreases momentarily

Ammonia is consumed in the reaction

To determine the effect of decreasing the volume on the contained gases in the reaction N2(g) + 3H2 ⇌ 2NH3(g), we need to consider Le Chatelier's Principle.

When the volume is decreased, the system will try to counteract the change by shifting in such a way to reduce the pressure. Since pressure is directly proportional to the number of gas molecules, the system will react by increasing the number of gas molecules.

In this reaction, there are 4 moles of gas molecules on the left side (N2 and 3H2) and 2 moles of gas molecules on the right side (2NH3). By increasing the number of gas molecules, the system will shift towards the side with more moles of gas, which in this case is the left side. Therefore, the reaction will shift towards the reactants (N2 and 3H2) when the volume is decreased.

So, the correct answer is:

The system reacts by increasing the number of gas molecules.