Energy Changes- Paper 1

Question 1

What is there always changes in whenever chemical reactions occur?

Answer 1

Energy

Question 2

Is energy created, moved around or destroyed in chemical reactions?

Answer 2

Moved around

Question 3

What is an exothermic reaction?

Answer 3

A reaction which transfers energy to the surroundings usually by heating-shown by a rise in temp

Question 4

Give an example of an exothermic reaction.

Answer 4

Burning fuels (combustion) which gives out a lot of energy. Or a neutralisation (acid+alkali) reaction.

Question 5

Are oxidisation reactions usually endothermic or exothermic?

Answer 5

Exothermic e.g. adding sodium to water releases energy.

Question 6

Give everyday examples of exothermic reactions.

Answer 6

Self heating cans of hot drink rely on exothermic reactions between chemicals in their bases.

Question 7

What is an endothermic reaction?

Answer 7

A reaction that takes in energy from the surroundings- shown by fall in temperature.

Question 8

Which are more common, exothermic or endothermic reactions?

Answer 8

Exothermic reactions.

Question 9

Example of endothermic reaction?

Answer 9

Citric acid and sodium hydrogencarbonate

Thermal decomposition e.g. heating calcium carbonate causes it to decompose into calcium oxide and carbon dioxide.

Question 10

Give some everyday examples of endothermic reactions

Answer 10

Sports injury packs- chemical reaction allows the pack to become instantly cooler without having to put it in the freezer.

Question 11

What equipment would you need to measure the amount of energy released by a chemical reaction?

Answer 11

Polystyrene cup, lid, thermometer, large beaker, cotton wool and the reaction mixture.

Question 12

Method for practical?

Answer 12

1. ) Put 25cm3 of 0.25mol/dm3 of hydrochloric acid and sodium hydroxide in seprate beakers.
2. ) Place the beakers in a water bath set to 25 degrees until they are both at the same temp.
3. )Add HCl followed by the NaOH to a polystyrene cup with a lid.
4. ) Take the temp of the mixture every 30 seconds and record the highest temp.
5. ) Repeat using 0.5 and 1mol/dcm3 of hydrochloric acid

Question 13

What does an exothermic reaction profile look like?

Answer 13

The curve will start mid graph, then curve up and then down far past the reactants point. That shows how much energy was released.

Question 14

What does an endothermic reaction profile look like?

Answer 14

The curve starts at the bottom (reactants) and curves up and then when it falls it stops mid way. This shows the energy absorbed.

Question 15

On a graph where does the activation energy measure?

Answer 15

From the reactants to the highest point of the curve.

Question 16

How does the graph show it’s endothermic?

Answer 16

Because the products are at a HIGHER energy than the reactants.

Question 17

How does the graph show it’s exothermic?

Answer 17

Because the products are at a LOWER energy than the reactants.

Question 18

What is an electrolyte?

Answer 18

A solution that can conduct electricity, e.g. a solution of an ionic compound.

Question 19

What is true about cells and how long they last?

Answer 19

They can only produce electricity for a certain period of time. Eventually the chemicals in the cells run out.

Question 20

When do cells produce electricity?

Answer 20

If we use metals with different reactivities.

Question 21

The size of the potential difference depends on….

Answer 21

the difference in reactivity between the metals.

also the electrolyte

Question 22

What is a battery?

Answer 22

A battery contains two or more cells connected in series to produce a greater voltage

Question 23

What is a non-rechargeable battery?

Answer 23

An alkaline battery as once the reactants run out no more electricity can be produced and there is no way to reverse this reaction.

Question 24

What is a rechargeable battery?

Answer 24

Rechargeable batteries can be recharged as we can reverse the chemical reactions we applying an electrical current.

Question 25

What do you react in a hydrogen cell?

Answer 25

hydrogen and air or pure oxygen.

Question 26

What is the only waste product of a hydrogen fuel cell?

Answer 26

Water

Question 27

What is the equation at the negative electrode?

Answer 27

2h2—> 4h+ +4e-

Question 28

What is happening to the hydrogen in the fuel cell?

Answer 28

It is becoming oxidised

Question 29

List the disadvantages of Rechargeable batteries

Answer 29

They become less efficient as they store less electricity the more charging cycles they go through and need replacing eventually.

They require recharging once they’ve run out

Question 30

List advantages of hydrogen fuel cells

Answer 30

Can be a source of drinking water e.g. on spacecraft

Don’t get less efficient the longer they run

Produce electricity for as long as you are providing hydrogen for them

Question 31

List advantages of rechargeable batteries

Answer 31

No dangerous fuels are required.

Produce a greater pd than a hydrogen fuel cell.

Question 32

List disadvantages of hydrogen fuel cells

Answer 32

Hydrogen is an explosive gas so difficult to store safely.

Produce a low pd so several are need together.

Question 33

Energy is….. when new bonds are formed

Answer 33

Energy is released when new bonds are formed.

Question 34

Bond formation is

Answer 34

Exothermic

Question 35

Bond breaking

Answer 35

Endothermic

Question 36

Energy must be …… to break existing bonds

Answer 36

Supplied.

Question 37

What are the 3 steps to calculating bond energy?

Answer 37

Find the energy required to break the bonds

Find energy released from the forming of new bonds

Find the overall energy change (CAN BE NEGATIVE)

Question 38

What IS activation energy?

Answer 38

Minimum amount of energy the reactants need to collide with each other and react.