Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

Transfers energy to surroundings

Question 2

What is an endothermic reaction?

Answer 2

Energy is transferred from the surroundings

Question 3

What does the energy change cause?

Answer 3

A temperature change

Question 4

Energy is always _________ in chemical reactions

Answer 4

Conserved

Question 5

What is a reaction profile?

Answer 5

Shows whether a reaction is exothermic or endothermic

Question 6

What is activation energy?

Answer 6

The minimum amount of energy particles must have to react when they collide

Question 7

What are “the surroundings”?

Answer 7

Everything that isn’t in the reaction

Question 8

What is breaking a bond?

Answer 8

Requires energy so is endothermic

Question 9

What is forming a bond?

Answer 9

Exothermic because it releases energy

Question 10

What are bonds?

Answer 10

Atoms are held together by strong chemical bonds. In a reaction, these bonds are broken and new bonds are formed.

Question 11

When is the overall reaction exothermic?

Answer 11

When more energy is released making bonds than required to break bonds

Question 12

When is the overall reaction endothermic?

Answer 12

If a less energy is released making the bonds than required to make the bonds

Question 13

What are bond calculations?

Answer 13

Energy required to break bonds - energy required to make bonds
Positive number = endothermic
Negative number = exothermic

Question 14

What are examples of exothermic reactions?

Answer 14

Oxidation
Combustion
Neutralisation

Question 15

What are everyday uses of exothermic reactions?

Answer 15

Self heating cans
Hand warmers

Question 16

What are examples of endothermic reactions?

Answer 16

Thermal decomposition
Citric acid and sodium hydrogen carbonate

Question 17

What are everyday uses of endothermic reactions?

Answer 17

Sports injury packs

Question 18

What are batteries?

Answer 18

Two or more cells connected in series

Question 19

Why are some batteries rechargeable?

Answer 19

An external electric current is applied which reverses the reaction

Question 20

Why are some batteries not rechargeable?

Answer 20

Some batteries, like alkaline batteries, are not rechargeable because the reaction is not reversible. Once the reactants are used up, the chemical reactions stops.

Question 21

What is a metal displacement reaction?

Answer 21

One metal is oxidised and loses electrons. These electrons are transferred to another metal, which gains electrons so is reduced.

Question 22

What is a chemical cell?

Answer 22

Uses the movement of electrons in a metal displacement reaction to generate a current.

Question 23

What does a greater difference in reactivity of metals lead to?

Answer 23

The greater the potential difference produced.

Question 24

What are hydrogen fuel cells?

Answer 24

Use a fuel and oxygen from the air to produce a potential difference.
Often generate electricity from hydrogen and oxygen
2 atoms of hydrogen are oxidised to form two molecules of water.

Question 25

What are the half equations in alkaline fuel cells?

Answer 25

2H2 + 4OH- –> 4H2O + 4e-
O2 + 2H2O + 4e- –> 4OH-

Question 26

What are advantages of hydrogen fuel cells?

Answer 26

Only waste is water
Do not need to be electrically recharged

Question 27

What are disadvantages of hydrogen fuel cells?

Answer 27

Hydrogen is highly flammable and hard to store
Hydrogen is often produced from non-renewable resources