UNIT 6 - Chemical Kinetics

Question 1

State the relationship between the half-life of the reactant and the order of the reaction.

Answer 1

If the reactant has a constant half-life then the reaction must be first order.

Question 2

Define rate-determining step of the reaction.

Answer 2

Slowest step of the reaction mechanism determining the overall rate of the reaction.

It’s transition state has the highest energy.

It’s activation energy will be equal the activation energy of the overall reaction.

Question 3

State the formula of average rate of reaction.

Answer 3

Arr = delta C/delta t

Question 4

State the relation between the energy of activation and temperature.

Answer 4

Independent.

Question 5

State and describe the main method of the determination of the order of a reaction.

Answer 5

Initial rates method.

Carry out a number of separate experiments with different starting concentrations of reactant A and measure the initial rate of each reaction.

if:

• changing the concentration of A -> no effect on the rate -> zero order with respect to A.
• changing the concentration of A -> directly proportional changes in the rate of reaction (if double [A] then double rate) -> first order.
• changing the concentration of A -> square of that change in the rate of reaction -> second order.

Question 6

State the initial rate of reaction formula.

Answer 6

Slope of the tangent to (0,0)

delta y/delta x

Question 7

List the parameters determining the rate of reaction.

Answer 7

• absorbance
• volume
• mass
• pH
• conductivity

Question 8

Define the order of reaction.

Answer 8

The power to which a particular reactants concentration is raise in the rate equation.

Overall order of reaction is the sum of the individual orders for all reactants.

Question 9

State and label the Arrhenius equation and it’s function.

Answer 9

k = Ae ^ -Ea/RT

A- Arrhenius constant, frequency factor, preexponential factor (takes into account the frequency with which successful collisions will occur)

k - rate constant

Question 10

Define rate of chemical reaction.

Answer 10

Increase in concentration of products or the decrease in concentration of reactants per unit of time.

delta C/delta t

Question 11

List the factors affecting the rate of the reaction.

Answer 11

• temperature
• concentration
• particle size
• pressure
• catalyst

Question 12

State what has an impact on the reaction?

Answer 12

• temperature
• concentration
• surface area
• catalyst

Question 13

Define quenching.

Answer 13

Technique used during titration where a substance is introduced which effectively stops the reaction in the sample at the moment.