Question

Which of the following theoretical factors decreases the rate of a reaction? (a) decrease collision frequency (b) decrease collision energy (c) ineffective collision orientation

Short answer

(a) decrease collision frequency, (b) decrease collision energy, and (c) ineffective collision orientation all decrease the rate of a reaction.

Step-by-step solution

Understanding Reaction Rate Factors

The rate of a chemical reaction depends on factors like collision frequency, collision energy, and collision orientation. Each of these factors contributes to how often and how effectively reactant particles meet and transform into products.

Analyzing Collision Frequency

Collision frequency describes how often reacting particles collide. A decrease in collision frequency implies that particles meet less often, leading to fewer opportunities for reactions to occur. Therefore, reduced collision frequency generally decreases the reaction rate.

Examining Collision Energy

Collision energy refers to the kinetic energy possessed by reacting particles at the time of collision. A higher energy means particles can overcome the activation energy barrier more easily. A decrease in collision energy means fewer particles have enough energy to react, thus reducing the reaction rate.

Considering Collision Orientation

For a reaction to occur, particles must collide in an orientation that allows them to rearrange into products. Ineffective collision orientation means that even if particles collide with enough energy, they still might not react unless oriented correctly. This factor also decreases the reaction rate.

Identifying the Decreasing Factors

Given the options (a), (b), and (c), each describes a factor that can decrease the rate of a reaction: (a) decrease collision frequency, (b) decrease collision energy, (c) ineffective collision orientation. All of these factors are theoretical reasons that can decrease the reaction rate.

Key concepts

Collision Frequency

Collision frequency is a fundamental factor in understanding how often reacting particles come into contact with one another. This is a crucial aspect in chemical reactions because the more frequent the collisions, the higher the chance that the particles will react with each other.

• *More Collisions = Higher Reaction Rate*: When particles collide more frequently, the opportunity for a reaction to occur increases, potentially speeding up the reaction.
• *Less Collisions = Lower Reaction Rate*: Conversely, if collision frequency decreases, there are fewer chances for the particles to interact, resulting in a slower reaction rate.

Factors that affect collision frequency include the concentration of reactants and the temperature of the reaction system. Increasing the concentration typically leads to more collisions, while higher temperatures can increase the particle movement, causing them to collide more often.

Collision Energy

The energy with which particles collide, known as collision energy, is essential for determining whether a reaction will occur. This energy is mainly the kinetic energy that particles possess as they move.

• *Activation Energy*: For a reaction to take place, the colliding particles must have enough energy to overcome the activation energy barrier, which is the minimum energy required to start a reaction.
• *High Energy Collisions*: If the particles collide with high enough energy, they are more likely to surpass this barrier and form products.
• *Low Energy Collisions*: On the flip side, if the collision energy is too low, particles will fail to overcome the activation energy barrier, which results in no reaction.

Therefore, ensuring that reacting particles have sufficient energy is vital for increasing the reaction rate. Factors like temperature influence collision energy, as higher temperatures increase the kinetic energy of particles.

Collision Orientation

Collision orientation refers to the positioning of colliding particles relative to each other during a reaction. It's not enough for particles just to collide with enough energy; they must also collide in the correct orientation.

• *Correct Orientation = Successful Reaction*: For a reaction to successfully occur, the orientation must allow for the necessary bonds to break and new bonds to form.
• *Incorrect Orientation = Failed Reaction*: Even with high collision frequency and sufficient energy, if the orientation is not suitable, the particles will not rearrange into products, and the reaction will not proceed.

Ensuring proper orientation typically involves relying on the randomness of particle movement and the natural tendency of particles to collide in multiple orientations until a successful one is achieved. This factor is often overlooked but is equally important in determining the reaction rate.