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Question 1

For a chemical reaction to occur, reactants must:

Answer 1

Physically collide

Have sufficient energy to react (ie, have the required activation energy)

Question 2

Rate of reaction can be increased by:

Answer 2

Increasing the frequency of collisions

Increasing energy of reactants

Lowering activation energy

Question 3

Effect of concentration on rate of reaction

Answer 3

By increasing the concentration (in aqueous solution), the number of reactant molecules per unit volume also increases.

This increases the frequency of collisions

Question 4

Effect of pressure on rate of reaction

Answer 4

By increasing the concentration (in gaseous substances), the number of reactant molecules per unit volume also increases.

This increases the frequency of collisions

Question 5

Effect of surface area on rate of reaction

Answer 5

By increasing the surface area (in solids) more of the reactant is exposed

This increases the frequency of collisions

Question 6

Effect of temperature area on rate of reaction

Answer 6

By increasing the temperature, the reactant molecule gains kinetic energy and more have sufficient energy to react (the activation energy).

This increases the frequency of collisions

Question 7

Effect of catalyst on rate of reaction

Answer 7

By adding a catalyst, the activation energy is lowered.

More have significant energy to react (activation energy)

This increases the frequency of collisions

Question 8

Define rate of reaction

Answer 8

The rate of reaction is defined as the change in concentration of a substance in unit time

Its usual unit is mol dm-3s-1

Question 9

How to measure rate of reaction

Answer 9

When a graph of concentration of reactant is plotted vs time, the gradient of the curve is the rate of reaction.

The initial rate is the rate at the start of the reaction where it is fastest.

Reaction rates can be calculated from graphs of concentration of reactants or products, by drawing a tangent to the curve (at different times) and calculating the gradient of the tangent.

Question 10

Description of Maxwell Boltzmann distribution graph

Answer 10

The energy distribution should never meet the x axis, as there is no maximum energy for molecules

The energy distribution should go through the origin because there are no molecules with no energy

The mean energy of the particles is not at the peak of the curve (slight to the right of it)

The area under the curve represents the total number of particles present

Only a few particles have energy greater than the EA

Modal energy this is the most probable energy - at peak

Question 11

What does the Maxwell-Boltzmann energy distribution show?

Answer 11

The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of a gas or liquid have at a particular temperature

Question 12

Maxwell-Boltzmann & Temperature

Answer 12

Curve shifts down and to the right

An increase in temperature, increases the kinetic energy of reactant particles and increases the number of particles with the required activation energy needed for them to react

This increases the frequency of collisions

Question 13

Maxwell-Boltzmann & Concentration

Answer 13

Curve shifts up. The area increases due to the increased number of particles

Question 14

Maxwell-Boltzmann & Catalyst

Answer 14

Curve does not change - the activation energy line shifts left

A larger number of particles now have sufficient energy to react

Question 15

Catalysts

Answer 15

Catalysts increase reaction rates without getting used up.

They do this by providing an alternative route or mechanism with a lower activation energy

Catalysts are not used up or chemically changed during this process

Question 16

Heterogeneous catalyst

Answer 16

A heterogeneous catalyst is in a different phase from the reactants

Heterogeneous catalysts are usually solids whereas the reactants are gaseous or in solution.

The reaction occurs at the surface of the catalyst.

Question 17

How do catalysts work?

Answer 17

Adsorption of reactants at active sites on the surface may lead to catalytic action.

The active site is the place where the reactants adsorb on to the surface of the catalyst.

This can result in the bonds within the reactant molecules becoming weaker, or the molecules being held in a more reactive configuration.

There will also be a higher concentration of reactants at the solid surface so leading to a higher collision frequency.

Question 18

Effect of pressure on heterogenous catalysis.

Answer 18

Increasing pressure has limited effect on the rate of heterogenous catalysed reactions because the reaction takes place on surface of the catalyst.

The active sites on the catalyst surface are already saturated with reactant molecules so increasing pressure wont have an effect.

Question 19

Industrial catalysts

Answer 19

Industrially catalysts speeds up the rate allowing lower temperature to be used (and hence lower energy costs) but have no effect on equilibrium.

Question 20

Environmental benefits of catalysts

Answer 20

Catalysed reactions can occur at lower temperature so less fuel needed and fewer emissions from fuels.

Catalysed reaction enables use of an alternative process with higher atom economy so meaning fewer raw materials needed and less waste products are produced