Consider the reaction between hydrogen gas and chlorine gas to form hydrogen chloride gas in a closed cylinder with a movable piston. H2 (g) + Cl2 (g) → 2 HCl (g) Predict what would happen to the reaction rate for a mixture containing both reactants if the following occur. (a) The pressure on the reaction mixture is increased at constant temperature (while keeping the reaction components in the gaseous phase).

In this case, the system doesn't be affected by the pressure change. This means that nothing will happen

Explanation:

We can answer this question applying the Le Chatelier's Principle. It says that changes on pressure, volume or temperature of an equilibrium reaction will change the reaction direction until it returns to the equilibrium condition again.

The results of these changes can define as:

Changes on pressure: the reaction will move depending the quantity of moles on each side of the reaction

Changes on temperature: The reaction will move depending on if it's endothermic or exothermic

Changes on volume: The reaction will move depending the limit reagent and the quantity of moles on each side of the reaction

In the exercise, they mention a change on pressure of the system at constant temperature (that means the temperature doesn't change). As Le Chatelier Principle's says, we must analyze what happens if the pressure increase or decrease. If pressure increase the reaction will move on the side that have less quantity of moles, otherwise, if the pressure decreases the reaction will move to the side that have more quantity of moles. In this case, we can see that both sides of the equation have the same number of moles (2 for the reactants and 2 for the products). So, in this case, we can conclude that, despite the change on pressure (increase or decrease), nothing will happen.