Chapter 18 - Rates of equations

Question 1

For reactant [A] and power n , give the equation for rate

Answer 1

rate proportional to [A]ⁿ

Question 2

What is a zero order reaction?

Answer 2

When concentration of a reactant has no effect on the rate

rate proportional to [A]⁰

Question 3

What is a first order reaction?

Answer 3

• Any change in concentration gives the same change to the rate
• rate proportional to [A]¹
  e. g. if [A] x 2, reaction rate increases by x 2

Question 4

What is a second order reaction?

Answer 4

• For any change in concentration, the rate changes by the square of the conc change
• rate proportional to [A]²
  e. g. if [A] x3, rate x9

Question 5

Give the rate equation for A and B - two reactants

Answer 5

rate = k [A]^m[B]ⁿ

where k = rate constant, m = order of reaction with respect to A and n = order of reaction with respect to B

Question 6

What is the rate constant?

Answer 6

• Proportionality constant
• Number that mathematically converts between the rate of reaction and concentration and orders

Question 7

How do you work out overall order of reaction?

Answer 7

Overall order = sum of orders with respect to each reactant

Question 8

How do you work out rate constant units?

Answer 8

1. ) Rearrange equation to make k the subject
2. ) Substitute units into expression for k
3. ) Cancel common units and show the final units on a single line

Question 9

What is initial rate?

Answer 9

Instantaneous rate at the beginning of an experiment when t=0

Question 10

How are concentration-time graph’s data collected?

Answer 10

Continuous monitoring

Question 11

Give the 3 methods of continuous monitoring of reactions?

Answer 11

• Monitoring by gas collection
• Monitoring by mass loss
• Monitoring by calorimetry

Question 12

How does a calorimeter work?

Answer 12

Wavelength of the light passing through a coloured solution is controlled using a filter. The amount of light absorbed by a solution is measured, which is directly linked to concentration of solution

Question 13

What is the gradient of a concentration-time graph?

Answer 13

rate of reaction

Question 14

Draw the concentration-time graph of a zero order reaction

Answer 14

Question 15

Draw the concentration-time graph of a first order reaction?

Answer 15

Question 16

What is half life?

Answer 16

Time taken for half of a reactant to be used up. Exponential decay pattern

Question 17

What is special about the half life in first order reactions?

Answer 17

Half life is constant

Question 18

How do you work out rate constant of first order reaction?

Answer 18

Draw tangent on concentration-time graph and calculate gradient, giving rate. Divide this by point of concentartion the tangent was drawn from

Question 19

What is the equation for rate constant from the half life?

Answer 19

k = ln2/ t(1/2)

Question 20

Draw a rate-concentartion graph for a zero order reaction

Answer 20

Question 21

Draw the rate-concentration graph for a first order reaction

Answer 21

Question 22

Draw a rate-concentration graph of a second order reaction

Answer 22

Question 23

What is the gradient of a rate-concentartion graph?

Answer 23

rate constant

Question 24

What is the rate-determining step?

Answer 24

slowest step in a multi-step reaction

Question 25

How can we predict reaction mechanisms? (using rate determining step)

Answer 25

• rate equation only includes reacting species involved in the rate-determining step.
• orders of the rate equation match the number of species involved in the rate-determining step

Question 26

What is the effect of increasing temperature by 10ºC on the rate?

Answer 26

Doubles the rate of reaction and rate constant

Question 27

What are the 2 factors that contribute to increased rate when temperature increases?

Answer 27

• Increasing the temperature shifts the boltzmann distribution to the right, increasing the proportion of particles that exceed the activation energy
• Particles move faster and collide more frequently

Question 28

What is the rate mainly determined on?

Answer 28

Ea

Question 29

Give the arrhenius equation

Answer 29

k = Ae^-Ea/RT

Question 30

What does the exponential factor (e) in arrhenius equation represent?

Answer 30

proportion of molecules that exceed Ea and have sufficient energy for a reaction to take place

Question 31

What does the pre-exponential factor (A) in the arrhenius equation represent?

Answer 31

Frequency of collisions with correct orientation

Question 32

Give the arrhenius equation in linear form

Answer 32

lnk = -Ea/RT + lnA

Question 33

Compare y=mx+c to linear arrhenius equation

Answer 33

y= mx+c

lnk = -Ea/RT 1/T + lnA

y-int - lnA

Gradient - -Ea/R