Kinetics

Question 1

What do kinetics tell us

Answer 1

How quickly a reaction takes place, so the rate of reaction

Question 2

What is rate

Answer 2

rate = change in concentration/ time

Question 3

For reaction aA + bB -> cC + dD how what equation is used for rate of reaction

Answer 3

rate = -(1/a x d[A]/dt)= -(1/b x d[B]/dt) = +(1/c x d[C]/dt) = +(1/d x d[D]/dt)

Question 4

What does the rate equation show

Answer 4

The rate equation for a chemical reaction shows how the rate depends on the concentration of the various reactions and products

Question 5

What is the rate equation

Answer 5

rate = d[A]/dt = -k[A]ⁿ

Question 6

What does k stand for in the rate equation

Answer 6

The rate constant

Question 7

What does n stand for in the rate equation

Answer 7

The reaction order

Question 8

What does the minus sign in the rate equation show

Answer 8

That the concentration of A falls with time and so it is a reactant and not a product

Question 9

How do you work out the total order of a reaction

Answer 9

Rate = k[A]^x x [B]^y x [C]^z

The total order of reaction is given by the sum of the individual orders:

total order = x + y + z

Question 10

If the total order of the reaction is 0 then what values could x, y, and z possess

Answer 10

x = 0, y = 0, z = 0

Question 11

If the total order of reaction is 1 then what values could x, y and z posess

Answer 11

x = 1, y = 0, z = 0

x = 0, y = 1, z = 0

x = 0, y = 0, z = 1

Question 12

If the total order of the reaction is 2 then what values could x, y, and z possess

Answer 12

x = 1, y = 1, z = 0

x = 1, y = 0, z = 1

x = 0, y = 1, z = 1

x = 2, y = 0, z = 0

x = 0, y =2, z = 0

x = 0, y = 0, z = 2

Question 13

For 0^th order of reaction what does n equal and how is this represented in the rate equation

Answer 13

n = 0 so k-[A]⁰ = 1

Question 14

For 1^st order of reaction what does n equal and how is this represented in the rate equation

Answer 14

n = 1 so k-[A]¹

Question 15

For 2nd order of reaction what does n equal and how is this represented in the rate equation

Answer 15

n = 2 so k-[A]²

Question 16

For a general reaction A + B -> C + D the rate equation is:

Rate = k[A]^m [B]n

What two things does this show

Answer 16

1. m and n tell you the orders of the reaction with respect to reactants A and B. m tells you how the concentration of reactant A affects the rate and n tells you that same for reactant B. If [A] changes and rate stays the same the order of reaction with respect to A is 0. So if [A] doubles/triples the rate will stay the same. If rate is proportional to [A] then the order of reaction with respect to A is 1. So if [A] doubles the rate will double, if A triples the rate will triple. If the rate is proportional to [A]² then the order of reaction with respect to A is 2. So if [A] doubles the rate will be 2²= 4x faster, if [A] triples the rate will be 3²= 9x faster.
2. The overall order of the reaction

Question 17

What does a graph for a 1^st order reaction look like

Answer 17

Question 18

What does a graph for a 2^nd order reaction look like

Answer 18

Question 19

What is the differential form of the rate equation

Answer 19

d[A]/dt = -k[A]

Question 20

What is the integrated form of the rate equation

Answer 20

ln[A] = ln[A]₀ - kt

or

[A] = [A]₀ exp(-kt)

Question 21

How do you calculate the half life of a first order reaction

Answer 21

[A] = [A]_o exp(-kt)

[A]_o / 2 = [A]₀ exp(-kt_1/2)

t_1/2 = ln(2) / k