Question

which of the following would increase the rate of a chemical reaction between hydrochloric acid (hcl) and solid zinc metal (zn)?

a) performing the reaction at a lower temperature

b) decreing the amount of zn

c) pulverizing the zinc metal into a fine powder

d) decreasing the concentration of hcl

Explanation:

Analyze the reaction and factors affecting its rate

The question asks which factor increases the rate of reaction between hydrochloric acid (\(\text{HCl}\)) and solid zinc metal (\(\text{Zn}\)). This is a heterogeneous reaction involving a solid reactant and an aqueous solution:

$$\text{Zn}(s) + 2\text{HCl}(aq) ightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)$$

According to collision theory, the rate of a Chemical Reactions process depends on the frequency of effective collisions between reactant particles.

Evaluate the effect of temperature (Option A)

Lowering the temperature decreases the average kinetic energy of the reactant particles. This leads to fewer collisions and fewer particles having the required activation energy, which decreases the reaction rate. Thus, Option A is incorrect.

Evaluate the effect of reactant amount (Option B)

Decreasing the amount of zinc does not increase the rate of reaction. In fact, reducing the quantity of a reactant generally decreases or has no positive effect on the initial rate of reaction. Thus, Option B is incorrect.

Evaluate the effect of surface area (Option C)

Pulverizing the solid zinc metal into a fine powder significantly increases its surface area. A larger surface area exposes more zinc atoms to the surrounding hydrochloric acid molecules simultaneously, increasing the frequency of collisions per unit time and thus increasing the reaction rate. Thus, Option C is correct.

Evaluate the effect of concentration (Option D)

Decreasing the concentration of \(\text{HCl}\) reduces the number of acid molecules per unit volume. This decreases the collision frequency between \(\text{H}^+\) ions and the zinc surface, which decreases the reaction rate. Thus, Option D is incorrect.

Answer:

• A) Performing the reaction at a lower temperature
• B) Decreasing the amount of Zn
• C) Pulverizing the zinc metal into a fine powder (Correct answer)
• D) Decreasing the concentration of HCl