7.2 Factors Affecting Reaction Rates

Short Answer Questions

1. What are the five main factors that affect reaction rate?
   Answer
   Size of reactant particles, concentration of reactants, temperature, presence of a catalyst, and pressure (for gases).
2. How does the size of reactant particles affect reaction rate?
   Answer
   Smaller particles have a larger surface area, leading to more frequent collisions and a faster reaction rate.
3. What happens to reaction rate when a reactant is in powdered form?
   Answer
   The reaction rate increases because the surface area available for reaction is larger.
4. Why do smaller marble chips react faster than larger ones with acid?
   Answer
   Smaller marble chips have a greater surface area, leading to more frequent collisions with acid particles.
5. What is concentration in terms of reaction rates?
   Answer
   Concentration refers to the amount of a substance in a given volume of solution.
6. How does increasing concentration affect the rate of reaction?
   Answer
   A higher concentration increases the number of reactant particles in a given space, leading to more frequent collisions and a higher reaction rate.
7. Why do reactions with concentrated acids occur faster than those with dilute acids?
   Answer
   Concentrated acids contain more hydrogen ions per unit volume, increasing the frequency of effective collisions.
8. How does temperature influence reaction rate?
   Answer
   Higher temperatures increase the kinetic energy of particles, making them move faster and collide more frequently with greater force.
9. What is activation energy?
   Answer
   Activation energy is the minimum amount of energy required for a reaction to occur.
10. Why does food spoil faster at higher temperatures?
    Answer
    Higher temperatures increase the rate of biochemical reactions responsible for spoilage.
11. What is a catalyst?
    Answer
    A catalyst is a substance that speeds up a chemical reaction without being consumed in the process.
12. How does a catalyst increase the rate of reaction?
    Answer
    A catalyst provides an alternative reaction pathway with lower activation energy, increasing the proportion of successful collisions.
13. What is an example of a catalyst used in industry?
    Answer
    Platinum is used in catalytic converters to reduce harmful emissions from vehicles.
14. What is an example of a biological catalyst?
    Answer
    Enzymes are biological catalysts that speed up biochemical reactions in living organisms.
15. How does pressure affect the reaction rate of gases?
    Answer
    Increasing pressure compresses gas molecules, leading to more frequent collisions and a higher reaction rate.
16. Give an example of an industrial reaction where pressure is used to increase reaction rate.
    Answer
    In the Haber process, high pressure increases the rate of ammonia formation from nitrogen and hydrogen.
17. Why does pressure have little effect on the reaction rate of solids and liquids?
    Answer
    Solids and liquids are not easily compressed, so increasing pressure does not significantly affect particle collisions.
18. How does a negative catalyst affect reaction rate?
    Answer
    A negative catalyst (inhibitor) slows down the reaction by increasing the activation energy or reducing the number of successful collisions.
19. What are two ways to control reaction rates in industrial processes?
    Answer
    Adjusting temperature and using catalysts.
20. How does surface area influence combustion reactions?
    Answer
    Smaller pieces of a substance burn faster because they have more exposed surface area for oxygen to react with.

Explanation Questions

1. Why do powdered reactants react faster than solid chunks of the same material?
   Answer
   Powdered reactants have a greater surface area, allowing more frequent collisions with reactant particles, increasing the reaction rate.
2. Why does increasing concentration not always lead to a directly proportional increase in reaction rate?
   Answer
   Some reactions have a limit where increasing concentration no longer significantly increases the number of effective collisions.
3. Why do higher temperatures lead to more successful collisions between particles?
   Answer
   At higher temperatures, particles move faster and collide with more energy, increasing the chances of overcoming activation energy.
4. Why does the presence of a catalyst not affect the final amount of product formed in a reaction?
   Answer
   A catalyst speeds up the reaction but does not alter the chemical equilibrium or the total yield of the reaction.
5. Why does pressure significantly impact the rate of gas reactions but not solid or liquid reactions?
   Answer
   Gases are compressible, so increasing pressure forces molecules closer together, leading to more collisions, whereas solids and liquids are incompressible.
6. Why is a catalyst important in industrial processes?
   Answer
   Catalysts reduce energy costs by speeding up reactions and allowing processes to occur at lower temperatures.
7. Why does manganese(IV) oxide speed up the decomposition of hydrogen peroxide?
   Answer
   It provides an alternative pathway with lower activation energy, allowing more molecules to react successfully.
8. Why does increasing surface area increase the rate of rusting in iron?
   Answer
   More exposed iron atoms are available to react with oxygen and water, leading to faster rust formation.
9. Why do enzymes work best at specific temperatures?
   Answer
   Extreme temperatures can denature enzymes, altering their shape and reducing their effectiveness as biological catalysts.
10. Why do reactions occur more quickly at higher pressures in gas-phase reactions?
    Answer
    More gas molecules are forced into a smaller space, leading to more frequent and energetic collisions.