[18.1] orders, rate equations, and rate constants

Question 1

what is the equation to measure rate of reaction?

Answer 1

change in concentration / change in time

Question 2

what is the rate equation?

Answer 2

• relates the concentrations of substances involved in a reaction to the rate of the reaction
• eg. A + B ➞ C

Question 3

what does the rate of reaction depend on?

Answer 3

• concentration of reactants
• constant k

Question 4

what do k, m, and n stand for in the rate equation?

Answer 4

• k is rate constant (units depend on values of m and n)
• m is order of reaction with respect to A
• n is order of reaction with respect to B

Question 5

what do you get if you add m + n?

Answer 5

overall order of the reaction

Question 6

what is zero order?

Answer 6

• concentration does not influence rate
• any number raised to the power of zero is 1

Question 7

what is first order?

Answer 7

• rate of reaction is directly proportional to [A]
• if [A] is doubled, reaction rate increases by factor of 2¹ = 2

Question 8

what is second order?

Answer 8

• rate of reaction is proportional to the square of [A]
• if [A] is doubled, reaction rate increases by factor of 2² = 4

Question 9

describe the rate equation for zero, first, and second order

Answer 9

• 0: rate = k[A]⁰ = k
• 1: rate = k[A]¹ = [A]
• 2: rate = k[A]² = [A]²

Question 10

describe the graphs for zero, first, and second order

Answer 10

• 0: straight line across
• 1: straight line graph through origin
• 2: exponential starting at origin

Question 11

how can you find the units for k?

Answer 11

1. rearrange the equation to make k the subject
2. substitute units into the expression for k
3. cancel common units

Question 12

what are the units of k for zero, first, and second order?

Answer 12

• 0: mol dm⁻³
• 1: s⁻¹
• 2: dm³ mol⁻¹ s⁻¹