Rates of Reactions October 2015

1) What is ALWAYS represented by the slope of the tangent to a graph of concentration vs. time for a reaction? a)The activation energy for the reaction b)The enthalpy change for the reaction c)The initial rate of the reaction d)The average rate of the reaction e)The instantaneous rate of the reaction

2) Which statement is false? a)ΔH forward is a positive quantity b)ΔH reverse is a negative quantity c)ΔH reverse is equal in magnitude to ΔH forward d)E a reverse is equal to E a forward e)E a reverse is less than E a forward

3) Which of the following statements is false? a)D is a reaction intermediate b)The overall reaction is endothermic c)E  G is the fastest step d)C  E is the rate determining step e)The reaction has a 3-step mechanism

4) In the following diagram, the letter which represents the position of the activated complex is: a)A b)B c)C d)D e)E

5) Which statement regarding the potential energy diagram below is false? a)The E a for the uncatalyzed reaction in the forward direction is +30 kJ b)ΔH for the uncatalyzed reverse reaction is +20 kJ c)The potential energy of the activated complex for the catalyzed reaction is +50 kJ d)The catalyst lowers the activation energy of the forward and reverse reactions by 20 kJ e)Ea the uncatalyzed reverse reaction is +70 kJ

6) The theoretical effect of an increase in the initial concentration of a reactant can be explained in terms of collision theory because it affects I.the collision geometry involved in the reaction II.the total number of collisions that occur III.the fraction of collisions that are effective IV.the required activation energy for a reaction a.both I and IV b.I, II and III are true c.both II and III d. both III and IV e. II only

7) The theoretical effect of a catalyst can be explained in terms of collision theory because it affects I.the collision geometry involved in the reaction II.the total number of collisions that occur III.the fraction of collisions that are effective IV.the required activation energy for a reaction a.both I and IV b. I, II and III are true c.both II and III d. both III and IV e.II only

8) The theoretical effect of an increase in temperature can be explained in terms of collision theory because it affects I.the collision geometry involved in the reaction II.the total number of collisions that occur III.the fraction of collisions that are effective IV.the required activation energy for a reaction a.both I and IV b.I, II and III are true c.both II and III d. both III and IV e. II only

9) For a reaction having ΔH of -42kJ and an activation energy of +63kJ, the activation energy for the reverse reaction is: a)105 kJ b)-105 kJ c)-63 kJ d)21 kJ e)-21 kJ

10) If the temperature is increased, how will the resulting graph differ from the one below? a)Both areas I and II will increase b)Both areas I and II will decrease c)Area I will increase and area II will decrease d)Area I will decrease and area II will increase e)Both areas I and II will remain the same

11) If a catalyst is added, what will happen to the activation energy? a)It will remain the same b)It will shift to the right c)It will shift to the left d)No prediction can be made

12) If the concentration of one of the reactants is increased, what will happen to areas I and II? a)Both area I and area II will increase by the same factor b)Area I will increase, area II will not c)Area II will increase, area I will not d)Area II will increase, area I will decrease

13) If E a1 represents the activation energy of reaction 1 and E a2 represents the activation energy of reaction 2, which statement is true when the temperature of both reactions increases? a)Reaction 1 will still be slower than reaction 2 b) Reaction 2 will become faster than reaction 1 c) Reaction 1 will increase in rate by a greater factor than reaction 2 d) Reaction 2 will increase in rate by a greater factor than reaction 1

14) What will happen to the height of the curve when the temperature increases? a)It will remain the same b)It will increase c)It will decrease d)It is difficult to predict

15) Which of the following statements is true if A is a reactant? a)The [A] vs time graph is a straight line if A is first order b)If A is zero-order, the [A] vs time graph is a horizontal line c)The 1/t vs [A] 2 graph is a straight line if A is second order d)If the rate vs [A] graph is an upward curve, then A must be second order