18.Kinetics

Question 1

What is the rate of a reaction

Answer 1

The change in concentration per unit time

Question 2

What is the rate expression for A + B —-> C

Answer 2

rate= [A]^m[B]^n

m and n are the orders of the reaction

Question 3

What is the overall order for the reaction for a reaction with the rate equation rate= [A]^m[B]^n

Answer 3

m + n

Question 4

What is the unit for the rate constant for a 0 order reaction

Answer 4

rate = k

moldm^-3 s^-1

Question 5

What is the unit for the rate constant for a 1 order reaction

Answer 5

rate = [A]

s^-1

Question 6

What is the unit for the rate constant for a 2 order reaction

Answer 6

rate = k[B][C]

mol^-1 dm^3 s^-1

Question 7

What is the unit for the rate constant for a 3 order reaction

Answer 7

rate = [D][E]^2

mol^-2 dm^6 s^-1

Question 8

What does a graph of rate v [A] look like is As order is 0

Answer 8

Horizontal line as the concentration of A doesn’t effect the rate

Question 9

What does a graph of rate v [A] look like is As order is 1

Answer 9

Directly proportional line as rate=[A]^1

Question 10

What does a graph of rate v [A] look like is As order is 2

Answer 10

Exponential line as rate=[A]^2

Question 11

What is the initial rate method

Answer 11

• a series of experiments each with different starting concentrations
• concentration vs time graph plotted
• tangent is drawn at t=0
• by drawing initial rate the conc. of all substances in the reaction mixture are known

Question 12

What does the effect of an increase of temperature have on k

Answer 12

Increases

Question 13

What does e^(-Ea/RT) show

Answer 13

The fraction of molecules with energy greater than the activation energy

• Ea is activation energy in Jmol-1
• R is gas constant
• T is temperature in K

Question 14

What is the Arrhenius equation

Answer 14

k=Ae^(-Ea/RT)
k-rate constant
A-pre-exponential factor
e^(-Ea/RT)-The fraction of molecules with energy greater than the activation energy

Question 15

What is the rate determining step

Answer 15

The slowest step in the reaction mechanism. It governs the rate of the overall reaction

Question 16

A+B+C ---> Y + Z
1. A + B ---> (fast) D
2. D ---> (slow) E
3. E + C ---> (fast)
What is the rate equation for this reaction

Answer 16

rate=[A][B][D]

2 is rate determining step but the rate of step 1 might effect the overall rate