Final answer:
In the reaction of magnesium metal with hydrochloric acid to produce hydrogen gas and aqueous magnesium chloride, increasing the pressure would not significantly affect the reaction rate, as solids and liquids are not compressible under moderate pressure changes.
Step-by-step explanation:
The effect of an increase in pressure on the reaction of magnesium metal with a solution of hydrochloric acid (Mg(s) + 2HCl(aq) → H2(g) + MgCl2(aq)) depends on the reaction conditions. If this system is at chemical equilibrium—where the rate of the forward reaction is equal to the rate of the reverse reaction—and involves gases, increasing the pressure will favor the direction in which there are fewer moles of gases. According to Le Chatelier's Principle, because the reactant side has solid magnesium and aqueous HCl, while the product side has gaseous hydrogen and aqueous magnesium chloride, increasing the pressure would shift the equilibrium to the left, potentially reducing the rate of the forward reaction.
However, this reaction is not typically presented as an equilibrium in introductory chemistry, and the scenario doesn't imply it is reversible under normal conditions. Therefore, in practice, the reaction rate of a solid and liquid reactant generating gas is usually unaffected by external pressure changes because solids and liquids are not compressible under moderate pressure changes. Thus, the reaction rate is mostly influenced by the surface area of the magnesium, the molarity of the hydrochloric acid, and the temperature of the solution.