Problem 55 - Chemistry Matter and Change

Question

Apply collision theory to explain why powdered zinc reacts to form hydrogen gas faster than large pieces of zinc when both are placed in hydrochloric acid solution.

Step-by-Step Solution

Answer

Applying collision theory, powdered zinc reacts faster with hydrochloric acid solution to produce hydrogen gas than large pieces of zinc due to its larger surface area. The increased surface area enables more frequent collisions between zinc and hydrochloric acid particles, resulting in a higher reaction rate.

Step 1: Understanding collision theory

Collision theory states that chemical reactions occur when molecules collide with each other with sufficient energy and the correct orientation. The number of successful collisions taking place per unit time depends on the concentration of the reactants and their physical and chemical properties.

Step 2: Comparing surface area of powdered and large pieces of zinc

When zinc is in powdered form, it has a larger surface area compared to a larger piece of zinc with the same mass. An increased surface area exposes more zinc atoms to the hydrochloric acid solution, which enables more collisions between the reactant particles.

Step 3: Analyzing the frequency of collisions

The greater the surface area of a reactant, the more frequent the collisions will be between the reactant particles. So, in the case of powdered zinc, which has a larger surface area, the frequency of collisions with hydrochloric acid molecules will be higher than that of large pieces of zinc.

Step 4: Examining the reaction rate

The reaction rate is directly proportional to the frequency of successful collisions. As mentioned earlier, the frequency of collisions is higher for powdered zinc due to its larger surface area. As a result, the reaction rate for powdered zinc reacting with hydrochloric acid solution to form hydrogen gas will be faster than that of the large pieces of zinc.

Step 5: Conclusion

Applying collision theory, we can conclude that powdered zinc reacts faster with hydrochloric acid solution to produce hydrogen gas than large pieces of zinc because the powdered form has a greater surface area. This increased surface area enables more frequent collisions between the zinc and hydrochloric acid particles, resulting in a higher reaction rate.

Key Concepts

Reaction Rate

The reaction rate of a chemical process is a measure of how quickly the reactants transform into products. It's essential to understand that the reaction rate hinges on various factors, one of which is the frequency of successful collisions between reactant molecules. When we talk about reaction rates, it's not just about how often particles collide, but whether these collisions are effective in breaking old bonds and forming new ones.

• Successful collisions must have enough energy to overcome the activation energy barrier, making energy a critical component.
• Additionally, molecules need to be oriented in a specific manner for a collision to lead to a reaction.

When more successful collisions occur per unit time, the reaction rate increases, resulting in a faster conversion of reactants to products.

Surface Area

The surface area of a reactant plays a pivotal role in determining the rate of a chemical reaction. Specifically, the surface area affects how many of the reactant's molecules are accessible for collisions.

• A larger surface area means that more atoms or molecules of the reactant are exposed and available to interact with other substances.
• For example, powdered substances have a much greater surface area compared to larger clumps or blocks of the same substance.

In the case of zinc reacting with hydrochloric acid, when zinc is in powdered form, it has a significantly increased surface area compared to large chunks of zinc. This amplified surface area results in more opportunities for zinc atoms to collide with hydrochloric acid molecules, thereby increasing the reaction rate.

Successful Collisions

For a chemical reaction to occur, not all collisions between molecules will count as successful. The concept of successful collisions is grounded in collision theory, which dictates that only those collisions that occur with adequate energy and proper alignment will lead to a reaction. Successful collision criteria:

• Energy: Colliding molecules must have enough kinetic energy to overcome the activation energy barrier, which is the minimum energy required for a reaction to take place.
• Orientation: Molecules must align in a way that allows old bonds to break and new ones to form.

Understanding successful collisions helps us appreciate why powdered zinc reacts more readily with hydrochloric acid than larger zinc pieces. Powdered zinc, having a higher frequency of collisions due to its increased surface area, also has more chances for those collisions to be successful, speeding up the reaction process.