Unit 2) Kinetics

Question 1

What is kinetics

Answer 1

The study of factors which alter the rates of chemical reaction

Question 2

What does the rate of a chemical reaction depend on ?

Answer 2

The rate of a chemical reaction normally depends on the concentration of the reactants
- the rate of a chemical reaction is monitored by the rate of change of the concentration

Question 3

Reactions can occur in ______ steps.

- the overall rate of a reaction may be held up by the ________ step

Answer 3

Multiple

Slowest

Question 4

Explanation Of orders

Answer 4

Look in notes and bright red page 44

Question 5

Consider reaction A +B —— > products

• If A is doubled and the reaction rate doubles what does this imply
• if B is doubled , and the reaction rate increases by a rate of 4 what does this imply

Answer 5

• implies the rate of reaction is directly proportional to the concentration of A so rate / [A] (to power 1)
  -implies that the rate is directly proportional to the square of the concentration of B rate / [B]2 (to power 2)
  Combining these results gives rate = k[A]1[B]2
  Where k is constant
  We say that the reaction is first order with respect to A and second order with respect to B

Question 6

What is the order of reaction

Answer 6

The order of a reaction with respect to any one reactant is the power to which the concentration of that reactant is raised in the rate equation

Question 7

What is the rate equation and what does everything in it mean

Answer 7

rate k[A]1[B]2

• 1 and 2 are the orders of the reaction with respect to A and B
• you will notice that they bear no relation to the stoichiometric coefficients a and b. The reaction is said to be first order with respect to A and second order with respect to B.
• the orders are usually small who numbers including zero and rarely greater than 2

Question 8

How is the overall order of the reaction given

Answer 8

By adding up all the powers (orders) so in the equation before the overall order would be 1+2=3

Question 9

What is the constant k in the rate equation known as

Answer 9

The constant k in the rate equation is known as the rate constant

Question 10

How do you calculate the rate constant k

Answer 10

k = rate /[A]1[B]2

Question 11

What are the units of the rate constant

Answer 11

The units of the rate constant vary depending on the overall order of the reactions. 
If the overall order of the reaction is 
0 - units are mol l-1 s-1
1 - units are s-1
2 - mol-1 l s-1
3 - mol-2 l2 s-1

Question 12

The rate equation for a chemical reaction can only be derived __________. Normally a series of experiments in which the initial concentration of the reactants are varied is carried out and the initial rate of reaction in each experiment is determined.

Answer 12

Experimentally

Question 13

How to work out orders

Answer 13

Look at brightred page 44

Question 14

Most reactions are believed to proceed in a ______ of steps rather than by one single step
What is this known as

Answer 14

Series

This is known as the reaction mechanism

Question 15

What is the slowest step in the reaction

Answer 15

The slowest step is called the rate determining step , and it governs the overall rate of the reaction

Question 16

If A and B are of order zero they won’t be _______ in the rate equation

Answer 16

Present

Question 17

What does the rate equation show

Answer 17

Shows the rate determining step and how much of each molecule is in the step