Chemistry C5 Energy Changes

Question 1

What happens in chemical reactions?

Answer 1

Energy changes

Question 2

What does energy change mean?

Answer 2

It means that energy moves around

Question 3

What can chemicals store?

Answer 3

Energy

Question 4

Do all chemicals store the same amount of energy?

Answer 4

No

Question 5

What are the two things produced in a reaction?

Answer 5

The reactant(s) going in and the product(s) as the result

Question 6

What happens if the products of a reaction store more energy than the original reactants?

Answer 6

They have taken in energy from the surroundings

Question 7

What happens if they store less?

Answer 7

It has been transferred to the surroundings

Question 8

Does the overall energy of the reaction go up or down?

Answer 8

It stays the same - this is why the amount of energy in the universe is constant and never increases or decreases

Question 9

What is reaction that gives out energy?

Answer 9

Exothermic

Question 10

How is exothermic energy normally given out?

Answer 10

By heat

Question 11

Give a common example

Answer 11

Burning fuels

Question 12

What is the burning of fuels also known as?

Answer 12

Combustion

Question 13

What is a nuetralisation reaction?

Answer 13

Its a reaction involving an acid and alkali

Question 14

Are neutralisation reactions exothermic?

Answer 14

Yes

Question 15

What is an oxidation reaction?

Answer 15

A reaction that gains Oxygen

Question 16

Is oxidation exothermic?

Answer 16

Sometimes

Question 17

Give an example of an exothermic oxidation reaction?

Answer 17

Adding sodium to water - sodium moves around the surface of the water as it is oxidised

Question 18

Give some examples of exothermic reactions

Answer 18

Hand warmers and some tinned drinks

Question 19

What is a reaction that takes heat in?

Answer 19

Endothermic

Question 20

Which are more common Exo- or Endo- thermic reactions?

Answer 20

Endothermic reactions are less common

Question 21

Give an example of an endothermic reaction?

Answer 21

Citric acid and sodium hydrogencarbonate

Question 22

Give another example of endothermic reaction?

Answer 22

Calcium carbonate + heat -> co2 + CaO (quicklime)

Question 23

Can you give some everyday endothermic reactions?

Answer 23

Athletic heating packs

Question 24

Can energy transfer be measured in thermic reactions?

Answer 24

Yes

Question 25

Describe how you would carry out a practical to measure the reaction?

Answer 25

Measure the temperature of the reactants and mix them in a polystyrene cup

Question 26

What is the biggest problem in these exercises?

Answer 26

That energy is lost to the environment

Question 27

What can you do to save heat

Answer 27

Pad the cup with wool and put a lid on the cup

Question 28

What kinds of reactions that this approach work well for?

Answer 28

Neutralisation reactions

Question 29

What other things can you control for?

Answer 29

Concentration and mass

Question 30

What is a reaction profile?

Answer 30

It shows the chemical potential energy as the reactants proceed to products

Question 31

What do you see in an exothermic reaction?

Answer 31

You see the end point lower than the starting point

Question 32

What does the height difference represent?

Answer 32

The energy change - its a direct measure of the loss

Question 33

What do you see in an endothermic reaction?

Answer 33

You see the endpoint higher

Question 34

What is the difference between the starting point and the top of the curve?

Answer 34

This is known as the activation energy.

Question 35

What does the activation energy represent?

Answer 35

It represents the minimum energy that the reactants need to collide and start the reaction

Question 36

Why do you need to supply this activation energy?

Answer 36

To break the bonds between molecules.

Question 37

What happens during a reaction in terms of bonds?

Answer 37

Old ones are broken and new ones formed.

Question 38

What direction does energy flow when breaking bonds?

Answer 38

It must be supplied - hence it is endothermic

Question 39

What direction does energy flow when forming bonds?

Answer 39

it is released hence it is exothermic