Rates

Question 1

Define rate of reaction

Answer 1

Concentration of product or reactant/ time

Question 2

What are the units of rate of reaction?

Answer 2

moles per dm cubed

Question 3

What is the effect of an increase in concentration on collisions?

Answer 3

Increases the frequency

Question 4

What is the effect on rate of reaction if particles collide more frequently?

Answer 4

Increases the rate of reaction

Question 5

What conditions must occur for particles to react?

Answer 5

Particles must collide and have energy which exceeds the activation energy

Question 6

Why does a higher pressure increase the rate of reaction?

Answer 6

• there are more particles in a given volume
• so collisions occur more frequently
• more frequent collisions mean a faster rate of reaction

Question 7

Give 3 ways the rate of reaction can be monitored

Answer 7

• measure loss in mass rate
• measure rate of gas produced
• measure change in numbers of ions using a conductivity metre
• measure colour change
• measure change in pH

Question 8

Why in the second half of a reaction is the rate slower?

Answer 8

Concentration of reactants gets lower so the frequency of collisions between particles decreases as there are fewer particles in a given volume

Question 9

How do you calculate rate of reaction for time t?

Answer 9

• draw a tangent at time t

- calculate the gradient of the line

Question 10

What is a catalyst?

Answer 10

A substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provides an alternative

Question 11

What is the effect of a catalyst on the overall enthalpy change of a reaction?

Answer 11

It has no effect on the overall enthalpy change

Question 12

What is a heterogeneous catalyst?

Answer 12

A catalyst with a different physical state from the reactants

Question 13

What is a homogeneous catalyst?

Answer 13

A catalyst with the same state as the reactants

Question 14

Give 2 examples of reactions with heterogeneous catalysts and name the catalysts

Answer 14

1) N2 + 2H2 —-> 2NH3 (Haber process) Iron

2) H2C=CH2 + H2 —–> CH3CH3 Nickel

Question 15

Give an example of a reaction with a homogeneous catalyst and name the catalyst

Answer 15

CH2=CH2 + H2O —-> CH3CH2OH

H3PO4 catalyst

Question 16

How do catalysts influence energy consumption and the effect of a reaction on the environment?

Answer 16

• Reactions using catalysts require less energy, less electricity, and less fossil fuel is used
• less of a resource is used
• using less fossil fuel produces fewer pollutants and cuts CO2 emissions which is linked to global warming

Question 17

How do catalysts affect atom economy and waste of a reaction?

Answer 17

• using a catalyst reduces waste

- improves atom economy

Question 18

What is the economic importance of catalytic processes?

Answer 18

• increases profitability of a reaction because product is made faster and less energy is used
• economic advantages of using a catalyst outweigh any costs associated with developing catalytic processes