energy changes

Question 1

What is conserved when chemical reactions occur?

Answer 1

Energy.

Question 2

What is the same at the beginning and the end of a chemical reaction in the universe?

Answer 2

The amount of energy.

Question 3

Exothermic reactions transfer…

Answer 3

Energy to the surroundings.

Question 4

In exothermic reactions, product molecules must have…

Answer 4

Less energy than the reactants.

Question 5

What are 3 scientific examples of exothermic reactions?

Answer 5

~Combustion
~Neutralisation
~Many oxidation reactions

Question 6

What is an everyday example of an exothermic reaction?

Answer 6

Hand warmers.

Question 7

Endothermic reactions take in…

Answer 7

Energy from the surroundings.

Question 8

In endothermic reactions, product molecules must have…

Answer 8

More energy than the reactants.

Question 9

What are 2 scientific examples of endothermic reactions?

Answer 9

~Thermal decomposition
~The reaction of citric acid and sodium hydrogen carbonate

Question 10

What is an everyday example of an endothermic reaction?

Answer 10

Sports injury packs.

Question 11

Chemical reactions only occur when…

Answer 11

Reacting particles collide with eachother with sufficient energy.

Question 12

What is activation energy?

Answer 12

The minimum amount of energy that particles must have to react.

Question 13

During a chemical reaction, energy must be supplied to…

Answer 13

Break bonds in the reactants.

Question 14

During a chemical reaction, energy is released when…

Answer 14

Bonds in the products are formed.

Question 15

What is the bond energies calculation?

Answer 15

Sum of energy taken in to break bonds - sum of energy released to form bonds = overall energy change

Question 16

If the energy taken in to break bonds is greater than the energy released when bonds are formed, what type of reaction is it and why?

Answer 16

Endothermic as the overall energy has been taken in.

Question 17

If the energy taken in to break bonds is smaller than the energy released when bonds are formed, what type of reaction is it and why?

Answer 17

Exothermic as the overall energy has been released.

Question 18

What so chemicals in cells react to produce?

Answer 18

Electricity.

Question 19

What is a factor that affects the voltage produced by a cell?

Answer 19

The type of electrode and electrolyte.

Question 20

How is a simple cell made?

Answer 20

By connecting 2 different metals in contact with an electrolyte.

Question 21

What is a battery?

Answer 21

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

Question 22

When do chemical reactions stop in non-rechargeable cells and batteries?

Answer 22

When one of the reactants is used up.

Question 23

What type of battery is non-rechargeable?

Answer 23

Alkaline batteries.

Question 24

Why can rechargeable cells and batteries be recharged?

Answer 24

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

Question 25

What are fuel cells supplied by?

Answer 25

An external source of fuel ( eg. hydrogen ) and oxygen.

Question 26

What does the fuel inside a fuel cell produce when it is oxidised electrochemically?

Answer 26

A potential difference.

Question 27

An overall reaction of a hydrogen fuel cell involves…

Answer 27

The oxidation of hydrogen to produce water.

Question 28

What are a potential alternative to rechargeable cells and batteries?

Answer 28

Hydrogen fuel cells.

Question 29

Hydrogen fuel cells can be used constantly as long as…

Answer 29

Fuel is continually being put in.

Question 30

Why are hydrogen fuel cells harder to transport than rechargeable cells and batteries?

Answer 30

As hydrogen is a gas and therefore needs to be stored at a high pressure.

Question 31

Why don’t rechargeable cells and batteries need to be constantly supplied?

Answer 31

As they can be recharged by reversing the reaction.

Question 32

Why are rechargeable cells and batteries hard to dispose of?

Answer 32

They are non-biodegradable.