What is the effect of pressure on the rate of gaseous reactions?

The rate of gaseous reactions generally increases with an increase in pressure.

Pressure is a significant factor in determining the rate of gaseous reactions. In a gaseous system, increasing the pressure effectively increases the concentration of the gas particles. This is because the same number of particles are now in a smaller volume, leading to more frequent collisions between the particles. According to the collision theory, the rate of a reaction depends on the frequency of collisions between reacting particles. Therefore, when the pressure is increased, the rate of reaction also increases.

However, it's important to note that this is generally true for reactions where the total number of gas molecules decreases. For example, in the reaction between nitrogen and hydrogen to form ammonia (N2 + 3H2 → 2NH3), the total number of gas molecules decreases from 4 to 2. In such reactions, an increase in pressure shifts the equilibrium to the right, favouring the forward reaction and thus increasing the rate of reaction.

On the other hand, if the total number of gas molecules increases in a reaction, an increase in pressure would favour the reverse reaction, potentially slowing down the overall rate of reaction. For instance, in the decomposition of ammonia into nitrogen and hydrogen (2NH3 → N2 + 3H2), the total number of gas molecules increases from 2 to 4. In this case, an increase in pressure would shift the equilibrium to the left, favouring the reverse reaction.

In summary, while an increase in pressure generally leads to an increase in the rate of gaseous reactions, the actual effect can vary depending on the specific reaction and the change in the number of gas molecules involved.