lecture 8 thermo

Question 1

When being asked to derive the rate law what do you need to do?

Answer 1

1. Write down a generalised equation (Rate = k[NO]x [Cl2]y for example)
2. Work out what X & Y are

Question 2

How do you figure out what Y is when deriving rate laws?

Answer 2

1. Choose 2 experiments where the conc of one reactant is the same in both experiments and the conc of the other reactant varies.
2. Divide them with the experiment with the higher rate on top
3. Put this in brackets with Y on the outside
4. Solve to find Y

Question 3

How do you figure out what x is when deriving rate laws?

Answer 3

1. Choose 2 experiments where the conc of one reactant is the same in both experiments and the conc of the other reactant varies.
2. Divide them with the experiment with the higher rate on top
3. Put this in brackets with X on the outside
4. Solve to find X

Question 4

Why is directly measuring the rate usually difficult?

Answer 4

Because the rates of reactions usually change with time

Question 5

In kinetics what do you use to determine the rate constant and reaction orders?

Answer 5

Intergrated rate equations using calculus

Question 6

What is the intergrated rate equation?

Answer 6

In ([R]t / [R]o) = -kt, using this equation you can calculate k (rate law)

Question 7

What does [R]t stand for?

Answer 7

Concentration of R at the time t

Question 8

What does [R]o stand for?

Answer 8

The concentration of R at the time t=0 (i.e inital [R])

Question 9

What is the half-life?

Answer 9

The time required for the concentration of a reactant to halve. Its application is used in chemistry and medicine to predict the concentration of a substance over time.

Question 10

For a first order reaction what is the intergrated rate law used to find the half-life?

Answer 10

t1/2 = In([R]t1/2 / [R]0) / k

Question 11

True or False? t1/2 does not depend on the concentration of the reactant

Answer 11

True

Question 12

True or False? If the time taken for the concentration to quarter to known K can be calculated

Answer 12

False, if the time taken for the concentration to halve is known, k, can be calculated

Question 13

What are the factors affecting rate?

Answer 13

Rate depends on conc of reactants (except for in 0 order reactions), also depends on k. And k depends on T

Question 14

k increases as what increases?

Answer 14

T

Question 15

What is the effect of a catalyst?

Answer 15

A catalyst increases the rate of a reaction by giving a different reaction pathway which has a lower activation energy.

Question 16

Are catalysts consumed in the reaction?

Answer 16

No

Question 17

Are large amounts or small amounts of catalysts usually needed?

Answer 17

Usually only small amounts

Question 18

Enzymes do what?

Answer 18

Catalyse biological reactions

Question 19

For a reaction to occur what must happen?

Answer 19

Reactants must collide with the correct orientation and with sufficient energy to initiate bond making and breaking. This energy requires is called the activation energy. All of this increases with temperature

Question 20

What is the activation energy Ea?

Answer 20

The sufficient energy required to initiate bond making and breaking in a reaction.

Question 21

True or False? As T increases there is an increased number of successful collisions with activation energy

Answer 21

True