7.4 Collision Theory

Short Answer Questions

1. What is collision theory?
   Answer
   Collision theory is a concept that explains how chemical reactions occur based on reactant particles colliding with sufficient energy and correct orientation.
2. What two conditions must be met for a collision to result in a reaction?
   Answer
   The particles must collide with sufficient energy (activation energy) and the correct orientation.
3. What is activation energy (Eₐ)?
   Answer
   Activation energy is the minimum amount of energy required for reactant particles to collide and form a reaction.
4. What is meant by an effective collision?
   Answer
   An effective collision is a collision between reactant particles that results in the formation of products.
5. What does an energy profile diagram represent?
   Answer
   An energy profile diagram represents the changes in potential energy of reactants and products throughout a chemical reaction.
6. How does temperature affect reaction rate?
   Answer
   Increasing temperature increases the kinetic energy of reactant particles, leading to more frequent and energetic collisions.
7. How does a catalyst affect the activation energy of a reaction?
   Answer
   A catalyst lowers the activation energy by providing an alternative reaction pathway.
8. What is the transition state in an energy profile diagram?
   Answer
   The transition state is the highest energy point in a reaction, representing an unstable intermediate.
9. What happens if reactant particles collide with incorrect orientation?
   Answer
   The collision will not result in a reaction, even if it has sufficient energy.
10. How does concentration affect the rate of reaction?
    Answer
    A higher concentration increases the frequency of collisions, raising the chances of effective collisions.
11. What is enthalpy change (ΔH) in an energy profile diagram?
    Answer
    Enthalpy change (ΔH) is the difference in energy between reactants and products, indicating if a reaction is exothermic or endothermic.
12. How does surface area affect reaction rate?
    Answer
    A greater surface area increases the number of exposed particles for collisions, raising the reaction rate.
13. Why do gases react faster than solids?
    Answer
    Gas particles move more freely and collide more frequently than solid particles.
14. How do catalysts increase the number of effective collisions?
    Answer
    Catalysts lower activation energy, allowing more particles to have enough energy to react.
15. What is the relationship between collision theory and reaction rates?
    Answer
    Reaction rate depends on the frequency of effective collisions between reactant particles.
16. Why do exothermic reactions have negative enthalpy change (ΔH)?
    Answer
    Exothermic reactions release heat, meaning the products have lower energy than the reactants.
17. Why do not all particles have the same kinetic energy?
    Answer
    At any temperature, particles have a range of kinetic energies due to random motion.
18. What is the activated complex in a reaction?
    Answer
    The activated complex is an unstable high-energy intermediate formed during the transition state.
19. How does particle orientation affect reaction success?
    Answer
    Particles must collide in a specific orientation to enable the correct bonds to break and form.
20. Why do some reactions occur slowly even if reactants are mixed?
    Answer
    If activation energy is too high or collisions are ineffective, the reaction proceeds slowly.

Explanation Questions

1. Explain why increasing temperature increases reaction rate.
   Answer
   Increasing temperature raises the kinetic energy of particles, leading to more frequent and energetic collisions, increasing the number of effective collisions.
2. Describe how catalysts lower activation energy.
   Answer
   Catalysts provide an alternative reaction pathway with a lower activation energy, allowing more particles to have sufficient energy to react.
3. Explain why a higher concentration of reactants leads to an increased reaction rate.
   Answer
   A higher concentration increases the number of particles per unit volume, increasing collision frequency and the likelihood of effective collisions.
4. Why do some exothermic reactions still require activation energy?
   Answer
   Even exothermic reactions need activation energy to break initial bonds before new bonds form and release energy.
5. How does surface area affect reaction rates in solid reactants?
   Answer
   Increasing surface area exposes more particles for collisions, increasing reaction rate.
6. Explain why a reaction with a very high activation energy is slow.
   Answer
   Few particles will have enough energy to overcome the activation barrier, leading to fewer effective collisions.
7. Explain why gases react faster than liquids and solids.
   Answer
   Gas particles move freely and have higher kinetic energy, leading to more frequent and energetic collisions compared to liquids and solids.
8. Why does a powdered solid react faster than a solid lump?
   Answer
   A powdered solid has a larger surface area, allowing more particles to be exposed to collisions, increasing the reaction rate.
9. Explain why an increase in pressure increases the rate of reaction for gases.
   Answer
   Increasing pressure forces gas particles closer together, increasing collision frequency and leading to a higher rate of reaction.
10. Why do some reactions occur spontaneously while others require an input of energy?
    Answer
    Spontaneous reactions release energy and have a low activation energy, while non-spontaneous reactions need an energy input to overcome activation barriers.