Final answer:
Lowering the pressure in a reaction system reduces the rate of reaction by decreasing particle collisions, explained by collision theory. Pressure affects the frequency of collisions, with less pressure meaning less frequent collisions and a slower reaction rate. Changes in pressure can also shift the equilibrium position of a reaction, further affecting the rate.
Step-by-step explanation:
Lowering the pressure reduces the rate of reaction because it impacts particle interactions. In terms of particles, pressure is directly related to how often they collide. When the pressure is high, particles are compressed and have less space to move, which increases the frequency of collisions. If we decrease the pressure - by increasing the volume of the container for example - particles will have more space and collide less often, reducing the reaction rate. This is explained by collision theory, which states that the rate of a reaction depends on the collision frequency between the reactant particles.
In a scenario where the pressure is lowered in a system at equilibrium, according to Le Châtelier's Principle, the system will shift to counteract this change - typically towards the side that produces more moles of gas, increasing the pressure back up. This change in equilibrium position can also affect the rate at which the forward and reverse reactions occur, ultimately impacting the rate of the overall reaction.