Describe the effect of each of the following on the rate of the reaction of magn

Question

Describe the effect of each of the following on the rate of the reaction of magnesium metal with a solution of hydrochloric acid: the molarity of the hydrochloric acid, the temperature of the solution, and the size of the pieces of magnesium. Account for the relationship between the rate of a reaction and its activation energy. In terms of collision theory, to which of the following is the rate of a chemical reaction proportional? the change in free energy per second the change in temperature per second the number of collisions per second the number of product molecules For each of the following pairs of reaction diagrams, identify which of the pair is catalyzed:

Explanation / Answer

4) The reaction is

Mg + 2 HCl ------> MgCl2 + H2

The rate of the reaction is given by

d[H2]/dt = k[Mg][HCl]2 where d[H2]/dt = rate of formation of H2 and the square braces denote molar concentrations.

i) Increase in molarity of HCl will increase the rate of the reaction and vice versa. As the molarity is increased, [HCl] increases and hence the rate increases.

ii) Increase in temperature usually increases the rate of the reaction. This is because, as the temperature is increased, the probability of collisions increases and hence the rate increases.

iii) As the size of the magnesium pieces is increased, the rate of the reaction becomes slower. This is because as the size increases, the surface area decreases. The reaction involves the contact of HCl with the magnesium pieces on the surface and a lower surface area leads to lower probability of contact and hence a slower reaction.

6) The rate of a chemical reaction is proportional to the number of collisions per second. As the number of collisions increases, the greater is the probability of product formation and hence the rate increases.

Ans: (c)

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