Using & Controlling Reactions: Rate of Reaction

Question 1

Activation Complex

Answer 1

= unstable intermediate from which the final product is formed
slow-moving particles do not form activated complex
fast-moving particles form the activated complex

Question 2

Rate of Reaction

Answer 2

= indicated by time taken for a reaction to reach specified change

• rate of reaction will change over time (best demonstrated by graph of products/reactants over time)
• average rate of reaction = slope of line between two points
• instantaneous rate of reaction = slope at any point in time

Question 3

Collision Theory

Answer 3

= for a reaction to occur:

• the reactant particles (molecules, atoms, ions) must collide
• colliding particles must have sufficient energy to form an activated complex
• collisions are productive or non-productive
• rate of reaction depends on: activation energy, frequency of collisions, energy of collisions

Question 4

Effect of Concentration on Reaction Rate

Answer 4

= as the concentration of reactants increases, reaction rate increases
… there are more particles per unit volume in more concentrated solutions, therefore higher frequency of collisions between reactants, therefore faster rate of reaction

Question 5

Effect of Temperature on Reaction Rate

Answer 5

= as temperature increases, reaction rate increases
… as the temperature increases, the particles move faster, therefore collisions have more energy and are more likely to be successful (form activated complex). Also, as the particles move faster the frequency of collisions increases

Question 6

Effect of Pressure on Reaction Rate

Answer 6

= as the pressure of a gaseous reaction mixture increases, reaction rate increases
… as pressure increases by decreasing volume, there are more particles per unit volume, therefore the frequency of collisions increases & thus reaction rate.

Question 7

Effect of State of Subdivision on Reaction Rate

Answer 7

= as the surface area of a solid increases, reaction rate increases
… SA:Vol ratio, particles can only react with the surface of the solid, therefore increased surface area = increased reaction rate (higher frequency of collisions)

Question 8

Effect of Catalysts on Reaction Rate

Answer 8

= presence of a catalyst increases the reaction rate; the catalyst is not consumed in the reaction
… provides an alternate pathway for the reaction which has lower activation energy, therefore more of the collisions have the energy required to form the activated complex, therefore higher frequency of productive collisions