C2.5 Chemical reactions

Question 1

What types of chemical reaction include a temperature change?

Answer 1

• dissolving
• neutralisation
• displacement
• precipitation

Question 2

What is neutralisation?

Answer 2

When an acid reacts with a base

Question 3

Are all combustion reactions exothermic or endothermic?

Answer 3

Exothermic

Question 4

What are explosions?

Answer 4

Exothermic reactions that release a lot of heat energy and gases very quickly

Question 5

What happens during an endothermic reaction?

Answer 5

They take in heat energy from surroundings so the temperature decreases

Question 6

What are three examples of endothermic reactions?

Answer 6

• ammonium nitrate in water
• sodium hydrogen carbonate with hydrochloric acid
• photosynthesis

Question 7

Why is breaking bonds an endothermic process?

Answer 7

Because it takes energy to break bonds which is taken from surroundings

Question 8

Why is making bonds an exothermic process?

Answer 8

Because energy is released when bonds are made

Question 9

Why is heat released in an exothermic reaction?

Answer 9

Less energy is needed to break the bonds in the reactants than it does to make the new bonds in the products, so heat energy is released

Question 10

Why is heat absorbed in an endothermic reaction?

Answer 10

More energy is needed to break the bonds of the reactants than it does to form new bonds between the products, so energy is absorbed

Question 11

What do energy diagrams show?

Answer 11

Changes during reactions

Question 12

Is rain naturally acidic or alkaline?

Answer 12

Acidic

Question 13

What is limestone made out of?

Answer 13

Calcium carbonate

Question 14

What are three things that affect the rate of a chemical reaction?

Answer 14

• temperature
• surface area of the solid
• concentration of the solutions

Question 15

What is the rate of a chemical reaction?

Answer 15

The speed at which it takes place

Question 16

What happens to the rate of reaction when you cool a reaction?

Answer 16

It slows down

Question 17

What is the concentration of a solution?

Answer 17

The measure of how much solute is dissolved in the solvent

Question 18

What must happen for a reaction to occur?

Answer 18

Particles of the reacting substances must collide with each other

Question 19

What must particles do to increase the rate of reaction?

Answer 19

• collide more frequently

- collide with a greater force

Question 20

How can you increase the rate of reaction?

Answer 20

• increase in temperature
• increase in concentration
• increase in surface area

Question 21

Why is increasing concentration effective in increasing the rate of reaction?

Answer 21

There are more solute particles in a given volume which means it is more likely the reactant particles will collide with one another

Question 22

Why does increasing temperature increase the rate of reaction?

Answer 22

Particles move faster which means there are more collisions and that when particles do collide they collide with more force which means they are more likely to react

Question 23

Why does surface area increase the rate of reaction?

Answer 23

Only the surface particles can be involved in a reaction in a solid, so the greater the surface area, the more particles there are that can collide

Question 24

What are catalysts?

Answer 24

Substances that speed up chemical reactions without being used up themselves

Question 25

Why are catalysts used?

Answer 25

To increase the rate of production of products

Question 26

What are three examples of a catalyst?

Answer 26

Iron, nickel and aluminium oxide

Question 27

How do catalysts save money and energy resources?

Answer 27

Reactions can be done at lower temperatures and pressures than they would be at usually, which means less energy is used

Question 28

What does the combustion of petrol in car engines produce?

Answer 28

Carbon monoxide and unburned hydrocarbons

Question 29

What do catalytic converters do?

Answer 29

They reduce the pollutants in exhaust gases by combining carbon monoxide and unburned petrol with oxygen from the air to produce carbon dioxide and water vapour

Question 30

How do catalytic converters work?

Answer 30

They use transition metals like platinum, rhodium and palladium to help speed up the reactions that remove pollutants in exhaust gases

Question 31

How are catalytic converters made as efficient as possible?

Answer 31

The catalyst has a fine honeycomb structure to increase surface area

Question 32

How is the amount of catalyst used in a catalytic converter minimised?

Answer 32

It is applied in a very thin surface coat