Chapter 6: Rates of Chemical Reactions

Question 1

Activation energy

Answer 1

• The energy required to break bonds of reactants so that a reaction can proceed
• Required for both endothermic and exothermic reactions

NOTE: Endothermic reactions have a larger activation energy.

Question 2

Collision theory

For a reaction to occur, reactants must…

Answer 2

• Collide with each other
• Have sufficient energy to break the reactants’ bonds
• Collide with the correct orientation to allow particular bonds to break and new bonds to form

Question 3

Rate of reaction

Answer 3

= change in concentration / time
Change in concentration of a reactant / product per unit of time

Question 4

Transition state

Answer 4

• New arrangement of atoms when activation energy is absorbed
• Occurs at the state of maximum energy potential
• Bonds are both breaking and forming at this stage
• Atoms in this state rearrange into products as the reaction progresses

Question 5

Activation energy and reaction rate

Answer 5

• Reactions only occur when the energy of a collision is equal to or greater than the activation energy
• Low activation energy = fast reaction rate
• High activation energy = slow reaction rate

Question 6

How can reaction rate be increased?

Answer 6

• ↑ frequency of successful collisions by increasing the number of collisions that can occur in a given time
• ↑ proportion of collisions that have energy that is equal or greater than or the activation energy by increasing the energy of all collisions

Question 7

Catalysts

Answer 7

• Provide an alternative reaction pathway with a lower activation energy to increase reaction rate
• They DO NOT change the value of △H for a reaction (as they do not alter extent of reaction)
• Not used up in the reaction (can be collected and reused)
• Can be homogeneous (same) or heterogeneous (different)

NOTE: Catalysts can speed up or slow down a chemical reaction.

Question 8

Effect of increasing temperature on reaction rate

Answer 8

• The proportion of successful collisions (collisions with energy greater than activation energy) increase
• The particles are moving faster (have higher kinetic energy), so there is a higher frequency of collisions per second