Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

Energy is transferred to the surroundings (exits)

Question 2

What happens to the temperature of an exothermic reaction?

Answer 2

Temperature increases

Question 3

What is an endothermic reaction?

Answer 3

Energy is taken in from the surroundings

Question 4

What happens to the temperature of an endothermic reaction?

Answer 4

Temperature decreases

Question 5

Give examples of exothermic reactions.

Answer 5

Combustion, Neutralisation, Respiration, Oxidation reactions, Self-heating cans, Hand warmers

Question 6

Give everyday uses of exothermic reactions.

Answer 6

Self-heating cans, Hand warmers

Question 7

Give examples of endothermic reactions.

Answer 7

Thermal decomposition, Photosynthesis, Citric acid and sodium hydrogen carbonate (sherbet)

Question 8

Give everyday uses of endothermic reactions.

Answer 8

Sports injury packs

Question 9

What is the energy of the products compared to reactants in an exothermic reaction?

Answer 9

Less

Question 10

What is the energy of the products compared to reactants in an endothermic reaction?

Answer 10

More

Question 11

What is activation energy?

Answer 11

Minimum energy that particles must have for a reaction to occur

Question 12

What does a reaction profile show?

Answer 12

It is a graphical representation of energy vs reaction (represented as a hump going from the reactants)

Question 13

What is needed to break a bond?

Answer 13

Energy is required to break a bond.

Question 14

What type of process is bond breaking?

Answer 14

Endothermic process.

Question 15

What is given out when a bond is made?

Answer 15

Energy is released when a bond is made.

Question 16

What type of process is bond making?

Answer 16

Exothermic process.

Question 17

Why is a reaction endothermic overall in terms of bonds breaking and making?

Answer 17

More energy is taken in during bond breaking than is given out during bond making.

Question 18

Why is a reaction exothermic overall in terms of bonds breaking and making?

Answer 18

More energy is given out during bond making than is taken in during bond breaking.

Question 19

How can you calculate the overall energy change in a reaction?

Answer 19

Sum of bonds broken - sum of bonds made (reactants - products).

Question 20

What do cells contain?

Answer 20

Cells contain chemicals which react to produce electricity.

Question 21

What is the voltage of a cell dependent on?

Answer 21

Type of electrode (different metals), concentration of electrolyte, and temperature.

Question 22

How can a simple cell be made?

Answer 22

By connecting two different metals with an electrolyte.

Question 23

What is an electrolyte?

Answer 23

A liquid that contains ions which react with the electrode.

Question 24

How does the voltage produced in a cell represent the reactivity of the metals?

Answer 24

The larger the difference in reactivity between the two metals, the larger the voltage.

Question 25

What is a battery?

Answer 25

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

Question 26

What are non-rechargeable cells and batteries?

Answer 26

The chemical reaction is irreversible and stops when one of the reactants has been used up.

Question 27

What is an example of a non-rechargeable battery?

Answer 27

Alkaline batteries are non-rechargeable.

Question 28

What are rechargeable cells and batteries?

Answer 28

Rechargeable cells and batteries can be recharged and used multiple times.

Question 29

What is a fuel cell?

Answer 29

A fuel cell is a device that converts chemical energy from a fuel into electricity through chemical reactions.

Question 30

How are fuel cells and chemical cells different?

Answer 30

Fuel cells oxidise the fuel electrochemically, while in chemical cells, the fuel is burned.

Question 31

What is a common fuel used in a fuel cell?

Answer 31

Hydrogen is a common fuel used in a fuel cell.

Question 32

What solutions can be used as the electrolyte in a hydrogen fuel cell?

Answer 32

An alkali (e.g., potassium hydroxide) or an acid (e.g., hydrochloric acid) can be used as the electrolyte.

Question 33

What happens at the negative electrode (anode) in a hydrogen fuel cell?

Answer 33

Hydrogen is oxidised, losing electrons. ## Footnote H2 → 2H* + 2e

Question 34

What happens at the positive electrode (cathode) if the electrolyte is an alkali?

Answer 34

Oxygen reacts with water to produce hydroxide ions, using up electrons.

Question 35

What happens at the positive electrode (cathode) if the electrolyte is an acid?

Answer 35

Oxygen is reduced, gaining electrons to form water. ## Footnote O2 + 4H* + 4e* → 2H2O

Question 36

What happens at the negative electrode (anode) if the electrolyte is an acid?

Answer 36

Hydrogen is oxidised, losing electrons. ## Footnote H2 → 2H* + 2e

Question 37

What is the overall equation for the hydrogen fuel cell?

Answer 37

2H2 + O2 → 2H2O ## Footnote Hydrogen + oxygen → water

Question 38

What are the requirements for fuel cells to produce voltage continuously?

Answer 38

A supply of a suitable fuel and oxygen are required.

Question 39

What are the advantages of a hydrogen fuel cell?

Answer 39

Advantages include no pollutants produced, only water and heat as byproducts, faster refueling, longer travel distances, and potential for renewability.

Question 40

What are the disadvantages of a hydrogen fuel cell?

Answer 40

Disadvantages include hydrogen being explosive, higher costs to refuel and manufacture, and limited hydrogen filling stations.