Topic 16 Kinetics 2

Question 1

What is reaction rate?

Answer 1

This is the measure of how fast a reaction takes place. This is calculated as the change in concentration of a reactant/product over unit time.

Question 2

What collision theory?

Answer 2

For particles to react they must collide with sufficient energy at the correct orientation.

Question 3

What is activation energy?

Answer 3

The minimum energy required to react.

Question 4

What is the Maxwell-Boltzmann distribution?

Answer 4

This is a graph that displays the number of particles (y axis) against energy (x axis). Activation energy (Ea) is also displayed on the graph to allow the number of particles with the Ea to be calculated.

Question 5

What factors effect rate?

Answer 5

Concentration –> Increased conc = particles are closer together ∴ there are more frequent successful collisions.

Surface area –> Increased surface area = more particles able to react ∴ there are more frequent successful collisions.

Pressure –> Increased pressure = particles are closer together ∴ there are more frequent successful collisions.

Temperature –> Increased temp = particles have a higher kinetic energy ∴ there are more frequent successful collisions.

Catalyst –> Use of a catalyst = Ea is reduced so more particles reach the Ea ∴ there are more frequent successful collisions.

Question 6

How can you calculate the rate of reaction using gradients?

Answer 6

On a graph displaying the change in factor (e.g. concentration) / time, calculating the gradient at a specific point (by drawing a tangent) will display the rate of the reaction at that point.

This can be done at multiple points to display the change in rate of reaction.

Question 7

What effects do zero, first and second orders have?

Answer 7

Zero - The reaction rate is proportional to [A]ᵒ (=1) and therefore the rate is not effected by any changes

First - The rate of reaction is proportional to [A]

Second - The rate of reaction is proportional to [A]²

Question 8

What is the rate equation and rate constant?

Answer 8

Equation - Rate = K[A]ᵐ[B]ⁿ (where [A] & [B] represent the concentration of the reactants in moldm⁻³)

Constant - K

Question 9

What is the Arrhenius equation?

Answer 9

K = Ae⁻ ᴱᵃ/ᴿᵀ / ln K = ln A - Eₐ/RT

Question 10

How can activation energy be calculated?

Answer 10

By rearranging ln K = ln A - Eₐ/RT

This is done by
Eₐ/RT = ln A - ln K
Eₐ = RT(ln A - ln K)

Question 11

What is the half-life of a reaction?

Answer 11

The time for the concentration of one of the reactants to fall by half.

Question 12

What are reaction orders and the overall order of a reaction?

Answer 12

Reaction orders - The powers m and n in K[A]ᵐ[B]ⁿ

Overall order of reaction - The sum of all orders for all substances that appear in the rate equation.
∴ m + n in K[A]ᵐ[B]ⁿ

Question 13

What is the mechanism of a reaction?

Answer 13

How the reaction takes place, displaying step by step the bonds that break and the new bonds that form.

Question 14

What is adsorption?

Answer 14

A process in which the atoms, molecules or ions are held on the surface of a solid.

Question 15

What is the rate-determining step?

Answer 15

In a multi-step reaction, this is the slowest step / the step with the highest activation energy.

Question 16

What are Sₙ1 & Sₙ2 reactions?

Answer 16

Sₙ1 - A nucleophilic substitution reaction with a mechanism that involves only one molecule or ion in the rate-determining step.

Sₙ2 - A nucleophilic substitution reaction with a mechanism that involves two molecules or ions in the rate-determining step.

Question 17

What is a transition state?

Answer 17

The state of the reacting atoms, molecules or ions when they are at the top of the activation energy barrier for a reaction step.

Question 18

What is a reaction profile?

Answer 18

A plot that shows how the total energy of the atoms, molecules or ions changes during the progress of a change from reactants to products.

Question 19

What is the gas constant?

Answer 19

This is the constant R in the ideal gas equation PV=nRT. The value of the constant depends on the units used for pressure and volume. If all quantities are in SI units, then R =8.314 JK⁻¹mol⁻¹.

Question 20

What is absolute temperature?

Answer 20

This is the temperature on the Kelvin (K) scale. The absolute zero temperature is at 0K, which is approximately -273ᵒC