College Chemistry: Kinetics - Reaction Rate, Average, Instantaneous

Concept Summary

• Reaction rate is a measure of the speed at which a chemical reaction occurs.
• Average reaction rate is the rate at which a reaction occurs over a specified time period.
• Instantaneous reaction rate is the rate at which a reaction occurs at a specific moment in time.
• Factors such as concentration, temperature, and surface area can affect reaction rate.
• Reaction rate can be measured using techniques such as rate of disappearance of reactants or appearance of products.

Questions

WHAT (definitional)

1. What is average reaction rate?
2. Answer: Average reaction rate is the rate at which a reaction occurs over a specified time period.
3. Real-world example: Measuring the average rate of a chemical reaction in a batch reactor.
4. Misconception cleared: Average reaction rate is not the same as instantaneous reaction rate, which is a snapshot of the reaction rate at a specific moment in time.
5. What is instantaneous reaction rate?
6. Answer: Instantaneous reaction rate is the rate at which a reaction occurs at a specific moment in time.
7. Real-world example: Measuring the instantaneous rate of a chemical reaction in a continuous flow reactor.
8. Misconception cleared: Instantaneous reaction rate is not the same as average reaction rate, which is a measure of the reaction rate over a specified time period.
9. What factors can affect reaction rate?
10. Answer: Factors such as concentration, temperature, and surface area can affect reaction rate.
11. Real-world example: Increasing the temperature of a reaction mixture to increase the reaction rate.
12. Misconception cleared: Reaction rate is not solely dependent on the concentration of reactants, but also on other factors such as temperature and surface area.

WHY (causal reasoning)

1. Why does increasing the concentration of reactants increase the reaction rate?
2. Answer: Increasing the concentration of reactants increases the frequency of collisions between reactant molecules, leading to a higher reaction rate.
3. Real-world example: Adding more catalyst to a reaction mixture to increase the reaction rate.
4. Misconception cleared: Increasing the concentration of reactants does not directly increase the reaction rate, but rather increases the frequency of collisions between reactant molecules.
5. Why does increasing the temperature of a reaction mixture increase the reaction rate?
6. Answer: Increasing the temperature of a reaction mixture increases the kinetic energy of reactant molecules, leading to a higher reaction rate.
7. Real-world example: Using a heat exchanger to increase the temperature of a reaction mixture.
8. Misconception cleared: Increasing the temperature of a reaction mixture does not directly increase the reaction rate, but rather increases the kinetic energy of reactant molecules.
9. Why does increasing the surface area of a catalyst increase the reaction rate?
10. Answer: Increasing the surface area of a catalyst increases the number of active sites available for reaction, leading to a higher reaction rate.
11. Real-world example: Using a catalyst with a high surface area, such as a porous metal oxide.
12. Misconception cleared: Increasing the surface area of a catalyst does not directly increase the reaction rate, but rather increases the number of active sites available for reaction.

HOW (process/application)

1. How can you measure the average reaction rate of a chemical reaction?
2. Answer: You can measure the average reaction rate of a chemical reaction by measuring the rate of disappearance of reactants or appearance of products over a specified time period.
3. Real-world example: Using a spectrophotometer to measure the rate of disappearance of a reactant.
4. Misconception cleared: Measuring the average reaction rate requires a specified time period, whereas instantaneous reaction rate is a snapshot of the reaction rate at a specific moment in time.
5. How can you measure the instantaneous reaction rate of a chemical reaction?
6. Answer: You can measure the instantaneous reaction rate of a chemical reaction by measuring the rate of disappearance of reactants or appearance of products at a specific moment in time.
7. Real-world example: Using a rapid mixing technique to measure the instantaneous reaction rate.
8. Misconception cleared: Measuring the instantaneous reaction rate requires a specific moment in time, whereas average reaction rate is a measure of the reaction rate over a specified time period.
9. How can you increase the reaction rate of a chemical reaction?
10. Answer: You can increase the reaction rate of a chemical reaction by increasing the concentration of reactants, increasing the temperature of the reaction mixture, or increasing the surface area of a catalyst.
11. Real-world example: Using a catalyst to increase the reaction rate of a chemical reaction.
12. Misconception cleared: Increasing the reaction rate requires a combination of factors, including concentration, temperature, and surface area.

CAN (possibility/conditions)

1. Can increasing the concentration of reactants always increase the reaction rate?
2. Answer: No, increasing the concentration of reactants can lead to a decrease in reaction rate if the reaction is diffusion-limited.
3. Real-world example: A reaction mixture with a high concentration of reactants that is diffusion-limited.
4. Misconception cleared: Increasing the concentration of reactants does not always increase the reaction rate, but rather depends on the specific reaction mechanism.
5. Can increasing the temperature of a reaction mixture always increase the reaction rate?
6. Answer: No, increasing the temperature of a reaction mixture can lead to a decrease in reaction rate if the reaction is thermally unstable.
7. Real-world example: A reaction mixture with a high temperature that is thermally unstable.
8. Misconception cleared: Increasing the temperature of a reaction mixture does not always increase the reaction rate, but rather depends on the specific reaction mechanism.
9. Can increasing the surface area of a catalyst always increase the reaction rate?
10. Answer: No, increasing the surface area of a catalyst can lead to a decrease in reaction rate if the catalyst is poisoned or deactivated.
11. Real-world example: A catalyst with a high surface area that is poisoned or deactivated.
12. Misconception cleared: Increasing the surface area of a catalyst does not always increase the reaction rate, but rather depends on the specific catalyst and reaction mechanism.

TRUE/FALSE (misconception testing)

1. Statement: Increasing the concentration of reactants always increases the reaction rate.
2. Answer: FALSE
3. Real-world example: A reaction mixture with a high concentration of reactants that is diffusion-limited.
4. Misconception cleared: Increasing the concentration of reactants does not always increase the reaction rate, but rather depends on the specific reaction mechanism.
5. Statement: Increasing the temperature of a reaction mixture always increases the reaction rate.
6. Answer: FALSE
7. Real-world example: A reaction mixture with a high temperature that is thermally unstable.
8. Misconception cleared: Increasing the temperature of a reaction mixture does not always increase the reaction rate, but rather depends on the specific reaction mechanism.
9. Statement: Increasing the surface area of a catalyst always increases the reaction rate.
10. Answer: FALSE
11. Real-world example: A catalyst with a high surface area that is poisoned or deactivated.
12. Misconception cleared: Increasing the surface area of a catalyst does not always increase the reaction rate, but rather depends on the specific catalyst and reaction mechanism.