C7.1 - Exothermic and endothermic reactions

Question 1

If you have ever warmed your hands near a fire, what would you have felt?

Answer 1

If you have ever warmed your hands near a fire, you would have felt the effects of energy being transferred during a chemical reaction

Question 2

Whenever chemical reactions take place, energy is always what?

Answer 2

Whenever chemical reactions take place, energy is always transferred

Question 3

Whenever chemical reactions take place, energy is always transferred, as chemical bonds in the reactants are broken and new ones are made in the products.
However, what remains the same before and after a reaction?

Answer 3

The total energy remains the same:
1. Before
2. After
a reaction

Question 4

Exothermic reactions

Answer 4

Exothermic reactions are reactions that transfer energy from the reacting chemicals to the surroundings

Question 5

What are many reactions?

Answer 5

Many reactions are exothermic reactions

Question 6

Exothermic reactions are reactions that transfer energy to the surroundings.
What does the energy transferred from the reacting chemicals often do?

Answer 6

The energy transferred from the reacting chemicals often heats up the surroundings

Question 7

Exothermic reactions are reactions that transfer energy to the surroundings.
The energy transferred from the reacting chemicals often heats up the surroundings.
As a result, what can you do as the exothermic reaction happens?

Answer 7

As a result, you can measure a rise in temperature as the exothermic reaction happens

Question 8

Many reactions are exothermic reactions.

What are other reactions?

Answer 8

Other reactions are endothermic reactions

Question 9

Endothermic reactions

Answer 9

Endothermic reactions are reactions that take in energy from the surroundings

Question 10

What happens as endothermic reactions take in energy from their surroundings?

Answer 10

As endothermic reactions take in energy from their surroundings, these reactions cause a fall in temperature as they happen

Question 11

Examples of exothermic reactions

Answer 11

Examples of exothermic reactions are:

1. The burning of fuels
2. Neutralisation reactions between acids and alkalis

Question 12

An example of an exothermic reaction is the burning of fuels, such as the combustion of methane gas.
What happens when methane burns?

Answer 12

When methane burns, it:

1. Gets oxidised
2. Releases energy to its surroundings

Question 13

You can easily measure the rise in temperature of exothermic reactions using what?

Answer 13

You can easily measure the rise in temperature of exothermic reactions using simple apparatus

Question 14

What happens when a fuel burns in oxygen?

Answer 14

When a fuel burns in oxygen, energy is transferred to the surroundings

Question 15

What do all warm-blooded animals rely on to keep their body temperatures steady?

Answer 15

All warm-blooded animals rely on exothermic reactions in respiration to keep their body temperatures steady

Question 16

What do the products of exothermic reactions have?

Answer 16

The products of exothermic reactions have a lower energy content than the reactants

Question 17

The products of exothermic reactions have a lower energy content than the reactants.
How are the actual differences in energy usually expressed?

Answer 17

The actual differences in energy are usually expressed in kilojoules per mole (kJ/mol)

Question 18

How common are endothermic reactions?

Answer 18

Endothermic reactions are much less common than exothermic reactions

Question 19

Examples of endothermic reactions

Answer 19

Examples of endothermic reactions are:

1. Thermal decomposition reactions
2. The reaction between citric acid and sodium hydrogencarbonate

Question 20

Why is the endothermic reaction of the reaction between citric acid and sodium hydrogencarbonate a good example to try in a lab?

Answer 20

The endothermic reaction of the reaction between citric acid and sodium hydrogencarbonate is a good example to try in a lab, because it is easy to measure the fall in temperature

Question 21

An example of a thermal decomposition reaction

Answer 21

An example of a thermal decomposition reaction is the decomposition of calcium carbonate

Question 22

An example of a thermal decomposition reaction is the decomposition of calcium carbonate.
When calcium carbonate is heated, it forms what?

Answer 22

When calcium carbonate is heated, it forms:

1. Calcium oxide
2. Carbon dioxide

Question 23

An example of a thermal decomposition reaction is the decomposition of calcium carbonate.
When calcium carbonate is heated, it forms calcium oxide and carbon dioxide.
When does this reaction only take place?

Answer 23

This reaction only takes place if you keep heating the calcium carbonate strongly

Question 24

When calcium carbonate is heated, it forms calcium oxide and carbon dioxide.
This reaction only takes place if you keep heating the calcium carbonate strongly.
What does the calcium carbonate need to do to be broken down?

Answer 24

The calcium carbonate needs to absorb energy from the surroundings to be broken down

Question 25

What do the products have in endothermic reactions?

Answer 25

In endothermic reactions, the products have a higher energy content than the reactants

Question 26

What can you feel when you eat sherbet?

Answer 26

When you eat sherbet, you can feel an endothermic reaction

Question 27

When you eat sherbet, you can feel an endothermic reaction. | What does sherbet dissolving in the water in your mouth take in?

Answer 27

Sherbet dissolving in the water in your mouth takes in energy

Question 28

When you eat sherbet, you can feel an endothermic reaction. Sherbet dissolving in the water in your mouth takes in energy. What does it do?

Answer 28

It provides a slight cooling effect

Question 29

Whenever chemical reactions take place, energy is always transferred, because what?

Answer 29

Whenever chemical reactions take place, energy is always transferred, because: 1. Chemical bonds in the reactants are broken 2. New chemical bonds are made in the products

Question 30

Endothermic reactions are reactions that take in energy from the surroundings. They transfer energy from what to what?

Answer 30

Endothermic reactions transfer energy from the surroundings to the reacting chemicals

Question 31

Examples of exothermic reactions are the burning of fuels, such as what, and neutralisation reactions between acids and alkalis?

Answer 31

Examples of exothermic reactions are: 1. The burning of fuels, such as the combustion of methane gas 2. Neutralisation reactions between acids and alkalis

Question 32

The main gas present in natural gas

Answer 32

The main gas present in natural gas is methane

Question 33

When calcium carbonate is heated, it forms calcium oxide and carbon dioxide. This reaction only takes place if you keep heating the calcium carbonate strongly. The calcium carbonate needs to absorb energy from the surroundings, such as what, to be broken down?

Answer 33

The calcium carbonate needs to absorb energy from the surroundings, such as the energy provided by a roaring Bunsen flame, to be broken down

Question 34

In endothermic reactions, the products have a higher energy content than the reactants, so what?

Answer 34

In endothermic reactions, the products have a higher energy content than the reactants, so energy is transferred from the surroundings