9: Rate Equations

Question 1

Give the formula for average rate of reaction.

Answer 1

             Change in Time

Question 2

Why does average rate of reaction decrease as the reaction proceeds?

Answer 2

Concentration of reactants decreases, so the probability of successful frequent collisions decreases.

Question 3

Give the equation for finding rate from straight line graphs.

Answer 3

Gradient = Change in Y
—————–
Change in X

Question 4

Give a general rate equation using A, B, M and N.

Answer 4

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

Question 5

What do reaction orders show?

Answer 5

How concentration of each reactant affects rate.

Question 6

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A changes but rate stays the same?

Answer 6

Zero.

Question 7

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A doubles but rate stays the same?

Answer 7

Zero.

Question 8

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A triples but rate stays the same?

Answer 8

Zero.

Question 9

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A is proportional to rate?

Answer 9

1

Question 10

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A doubles and rate doubles?

Answer 10

1

Question 11

For this rate equation, Rate = k [A]^m [B]^n, what would order with respect to A be when A triples and rate triples?

Answer 11

1

Question 12

For this rate equation, Rate = k [A]^m [B]^n, if rate is proportional to [A]^2, what will order with respect to A be?

Answer 12

2

Question 13

For this rate equation, Rate = k [A]^m [B]^n, if order with respect to [A] is 2 and the concentration of A doubles, what will the new rate be?

Answer 13

Rate will square, so the new rate will be 4x faster.

Question 14

For this rate equation, Rate = k [A]^m [B]^n, if order with respect to [A] is 2 and the concentration of A triples, what will the new rate be?

Answer 14

Rate will cube, so the new rate will be 9x faster.

Question 15

What 2 things does the rate constant link together?

Answer 15

Rate of reaction to concentration of reactants.

Question 16

The bigger the rate constant, the faster the…

Answer 16

Rate if reaction.

Question 17

If the orders for each reactant are 1 and 2, what will the overall order of reaction be?

Answer 17

3

Question 18

Will rate constant increase, decrease or stay the same if temperature increases?

Answer 18

Rate constant will increase as temperature increases.

Question 19

How can we be sure that temperature increase has affected rate and nothing else?

Answer 19

Concentration or orders of reactants haven’t changed so an increase in K, which is affected by temperature, increases rate.

Question 20

Draw a graph/describe the shape of a graph showing zero order and concentration.

Answer 20

Linear, similar to a negative correalation graph.

Question 21

Draw a graph/describe the shape of a graph showing first order and concentration.

Answer 21

Reciprocal graph shape.

Question 22

Draw a graph/describe the shape of a graph showing second order and concentration.

Answer 22

Exponential graph shape, but backwards.

Question 23

Draw a graph/describe the shape of a graph showing zero order and rate.

Answer 23

A flat line, halfway up the centre of the graph.

Question 24

Draw a graph/describe the shape of a graph showing first order and rate.

Answer 24

Linear, straight line. Like a positive correlation.

Question 25

Draw a graph/describe the shape of a graph showing second order and rate.

Answer 25

Half a quadratic graph.

Question 26

What is the rate determining step?

Answer 26

The ‘bottle neck’ in the reaction, where the slowest point in the reaction occurs.

Question 27

The rate determining step can be used to find what about a chemical reaction?

Answer 27

The reaction mechanism.

Question 28

How do we know if a reactant will have an impact on the rate of reaction?

Answer 28

The reactant will be present in the rate equation.

Question 29

What does the Arrhenius equation show?

Answer 29

The Arrhenius equation shows how the rate constant varies with temperature and activation energy.

Question 30

What are the units for activation energy?

Answer 30

Jmol-1

Question 31

What will happen to K in the Arrhenius equation if activation energy gets bigger?

Answer 31

K gets smaller.

Question 32

What happens to rate constant if temperature rises in the Arrhenius equation?
Why?

Answer 32

Rate constant increases.
This is because higher temperatures increase the kinetic energy of reactant particles so they are more likely to collide, increasing rate of reaction.

Question 33

Give the Arrhenius equation rearranged for activation energy.

Answer 33

Ea = (In (A) - In (K)) x RT

Question 34

Give the Arrhenius equation rearranged for temperature.

Answer 34

T = Ea
———————-
R (In (A) - In (K) )