Magnesium metal reacts vigorously with aqueous hydrochloric acid according to the equation
Mg(s) + 2 HCl(aq) → MgCl₂(aq) + H₂(g)
A student places identical strips of polished magnesium ribbon into three separate beakers, each containing 50.0 mL of 1.0 M HCl. Only the temperature of the acid solution is varied. The time required for the magnesium to disappear completely is recorded.
Temperature (°C) | Time for Mg to disappear (s)
15 | 98
25 | 62
35 | 40
Answer the following questions about the experiment.
(a) Describe the relationship between the temperature of the hydrochloric acid solution and the observed time required for the magnesium ribbon to dissolve.
(b) Using a particulate-level description of molecular collisions, explain why the reaction proceeds more rapidly as the temperature is increased from 15 °C to 35 °C.
(c) Predict qualitatively how the reaction time would change if the experiment were repeated at 5 °C, and justify your prediction.
(d) Identify one underlying assumption in the explanation you provided in part (b) that could become invalid if the temperature were raised far above 60 °C, and briefly explain how violating that assumption might alter the rate–temperature relationship.