Topic 5 - Energy Changes

Question 1

What happens to energy in chemical reactions?

Answer 1

It is conserved

Question 2

Is energy lost during chemical reactions?

Answer 2

No it is transferred but never lost

Question 3

What is an exothermic reactions?

Answer 3

Transfers energy to the surroundings so the temperature of the surroundings increases

Question 4

Give examples of exothermic reactions

Answer 4

Combustion, oxidation, neutralisation

Question 5

Give examples of everyday uses exothermic reactions?

Answer 5

Self heating cans and handwarmers

Question 6

What is an endothermic reaction?

Answer 6

One that takes energy in from the surroundings to the temperature of the surroundings decreases

Question 7

Give examples of endothermic reactions

Answer 7

Thermal decompositions

The reaction of citric acid and sodium hydrogencarbonate

Question 8

Give an example of everyday use of endothermic reactions

Answer 8

Sports injury packs

Question 9

When can chemical reactions occur?

Answer 9

Only when reacting particles collide with each other and with sufficient energy

Question 10

What is activation energy?

Answer 10

The minimum amount of energy that particles must have to react

Question 11

What do reaction profiles show?

Answer 11

The relative energies of reactants and products
The activation energy
The overall energy change of a reaction

Question 12

What needs to happen during a chemical reaction?

Answer 12

Energy must be supplied to break bonds in the reactants

Energy is released when bonds in the products are formed

Question 13

Describe the bond energies of an endothermic reaction?

Answer 13

The energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 14

What do cells contain?

Answer 14

Chemicals which react to produce electricity

Question 15

What is the voltage produced by a self dependent on?

Answer 15

Type of electrode and electrolyte

Question 16

How can you make a simple cell?

Answer 16

Connecting to different metals in contact with an electrolytes

Question 17

What do batteries consist of?

Answer 17

Two or more cells connected together in a series to provide greater voltage

Question 18

What happens to chemical reactions in nonrechargeable cells and batteries?

Answer 18

They stop when one of the reactants has been used up

Question 19

Give an example of a non-rechargeable battery

Answer 19

Alkaline batteries

Question 20

Why can rechargeable cells and batteries be recharged?

Answer 20

Because the chemical reactions are reversed when an external electrical current is supplied

Question 21

What are fuel cells?

Answer 21

They are supplied by an external source of fuel and oxygen or air

Question 22

How do fuel cells work?

Answer 22

The fuel is oxidised electrochemically within the fuel cell to produce a potential difference

Question 23

What does the overall reaction in a hydrogen fuel cell involve?

Answer 23

The oxidation of hydrogen to produce water

Question 24

Why are fuel cells better for the environment?

Answer 24

Don’t produce as many pollutants