Energy Changes

Question 1

What happens in endothermic reaction?

Answer 1

In an endothermic reaction:

✅ Energy is taken in from the surroundings (usually as heat)
✅ The temperature of the surroundings decreases
✅ The products have more energy than the reactants
✅ Bond breaking requires energy (more than is released when forming bonds)

Question 1

What happens in exothermic?

Answer 1

✅ Energy is released to the surroundings (usually as heat)
✅ The temperature of the surroundings increases
✅ The products have less energy than the reactants
✅ Bond formation releases energy (more than is used to break bonds)

Question 2

What is the activation energy?

Answer 2

🔥 Activation energy is the minimum amount of energy that particles must have to start a chemical reaction.

Question 3

what does energy change mean?

Answer 3

Energy change is the amount of energy transferred during a chemical reaction. It tells us whether energy is:

Released to the surroundings (exothermic) or

Taken in from the surroundings (endothermic).

Question 4

what is exothermic reaction

Answer 4

A reaction that transfers energy to the surroundings, usually as heat, causing the temperature to increase.

Question 5

What is an endothermic reaction?

Answer 5

A reaction that takes in energy from the surroundings, causing the temperature to decrease.

Question 6

What happens to temperature in an exothermic reaction?

Answer 6

The temperature of the surroundings increases.

Question 7

What happens to temperature in an endothermic reaction?

Answer 7

The temperature of the surroundings decreases.

Question 8

Give two examples of exothermic reactions.

Answer 8

Combustion

Neutralisation (acid + alkali)

Question 9

Give two examples of endothermic reactions.

Answer 9

Thermal decomposition

Citric acid + sodium hydrogen carbonate (used in cool packs)

Question 10

Is bond breaking exothermic or endothermic?

Answer 10

Endothermic – it takes in energy to break bonds.

Question 11

is bond forming exothermic or endothermic?

Answer 11

Exothermic – it releases energy when new bonds are formed.

Question 12

: What is the overall energy change in a reaction?

Answer 12

Energy to break bonds minus energy released when bonds are formed.
(Reactants – Products)

Question 13

What does a negative energy change mean?

Answer 13

The reaction is exothermic (more energy released than absorbed).

Question 14

What does a positive energy change mean?

Answer 14

The reaction is endothermic (more energy absorbed than released).

Question 15

What is the unit for bond energies?

Answer 15

Kilojoules per mole (kJ/mol)

Question 16

What kind of reaction happens in self-heating cans?

Answer 16

Exothermic

Question 17

What equipment could be used to measure temperature change in a simple school experiment?

Answer 17

A thermometer, a polystyrene cup (for insulation), and a lid.

Question 18

What kind of reaction happens in cold packs used in sports injuries?

Answer 18

Endothermic

Question 19

Why is thermal decomposition an endothermic process?

Answer 19

Because it requires energy to break chemical bonds in the compound.

Question 20

What’s a simple way to identify if a reaction is exothermic or endothermic in the lab?

Answer 20

Measure the temperature change during the reaction.

Question 21

In a bond energy calculation, what indicates the reaction is exothermic?

Answer 21

The total energy released from forming bonds is greater than the energy used to break them.

Question 22

What is meant by the term “energy profile diagram”?

Answer 22

: A graph showing the energy levels of reactants and products in a reaction.

Question 23

How does an energy profile diagram for an exothermic reaction look?

Answer 23

Products are at a lower energy level than reactants; energy is released.

Question 24

How does an energy profile diagram for an endothermic reaction look?

Answer 24

: Products are at a higher energy level than reactants; energy is taken in.

Question 25

What label is at the top of the curve in an energy profile diagram?

Answer 25

Activation energy – the minimum energy needed to start the reaction.

Question 26

: What does the area between reactants and products on an energy profile diagram represent?

Answer 26

The overall energy change of the reaction.

Question 27

🔥 Examples of exothermic reactions

Answer 27

Examples of exothermic reactions: Combustion (burning fuels) Neutralisation (acid + alkali) Respiration Self-heating cans

Question 28

❄️ Examples of endothermic reactions:

Answer 28

Thermal decomposition (e.g. calcium carbonate → calcium oxide + CO₂) Citric acid + sodium hydrogencarbonate Photosynthesis Instant cold packs

Question 30

required practical on temperature changes 🧪 Method For exothermic reaction

Answer 30

Use a polystyrene cup and put it inside a beaker. Add 25 cm³ hydrochloric acid to the cup. Measure and record the starting temperature. Add 25 cm³ sodium hydroxide. Put a lid quickly to reduce heat loss to the surrounding. Stir and measure the maximum temperature. Repeat to get average results or change variables like concentration.

Question 31

🧠 Why do you quickly put the lid on the polystyrene cup?

Answer 31

✅ To reduce heat loss to the surroundings ✅ So the temperature change is more accurate ✅ Prevents evaporation or cooling by air ✅ Helps keep the reaction as insulated as possible

Question 32

❄️ Method (for endothermic reaction)

Answer 32

Try citric acid + sodium hydrogencarbonate: Place citric acid solution in the polystyrene cup. Record starting temperature. Add sodium hydrogencarbonate and stir. Record lowest temperature reached.

Question 33

what is the endothermic reaction in the practical The thing you change in the experiment

Answer 33

The reactant (e.g. type of acid or metal) The concentration of acid or alkali The volume of one of the reactants

Question 34

what is ✅ Dependent variable The thing you measure

Answer 34

Temperature change (measured with a thermometer)

Question 35

✅ Control variables The things you keep the same to make it a fair test

Answer 35

Volume of acid or alkali used Concentration of the acid or alkali Mass of solid reactant (e.g. magnesium or sodium carbonate) Same equipment (e.g. same polystyrene cup, same thermometer) Starting temperature of reactants (ideally room temp) Same method for stirring

Question 36

What type of energy is required to break bonds?

Answer 36

endothermic reaction because lots of energy is required to break energy

Question 37

what type of energy is required to make bonds?

Answer 37

exothermic reaction