Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

They transfer energy from the reacting molecules to the surroundings which means the the temperature of the surroundings increases.

Question 2

What are some examples of exothermic reactions?

Answer 2

-Combustion (burning)
-Oxidation reactions
-Neutralisation

Question 3

What are the uses of exothermic reactions?

Answer 3

-Hand warmers
-Self-heating cans e.g. For food or drink

Question 4

What is an endothermic reaction?

Answer 4

They take in energy from their surroundings which means the temperature of the surroundings decreases.

Question 5

What is an example of endothermic reactions?

Answer 5

-Thermal decomposition

Question 6

What are the uses of endothermic reactions?

Answer 6

-Instant ice packs which can treat sports injuries

Question 7

What is the activation energy?

Answer 7

The minimum amount of energy that particles must have in order to react.

Question 8

What reaction happens when we break a bond?

Answer 8

Endothermic reaction as it requires energy

Question 9

What reaction happens when we form a bond?

Answer 9

Exothermic reaction as it releases energy

Question 10

(Triple only) What is an electrolyte?

Answer 10

A solution that can conduct electricity, for example a solution of an ionic compound.

Question 11

(Triple only) How can two different metals produce electricity?

Answer 11

If we take two different metals and place them into an electrolyte then we can produce electricity.

Question 12

(Triple only) How can cells produce electricity?

Answer 12

By using metals with different reactivites, however they can only produce electricity for a certain period of time before the chemicals in the cell run out and the reaction stops.

Question 13

(Triple only) How can the reactivity series be used to produce a greater potential difference?

Answer 13

The greater the difference between the reactivity of the metals, the greater the potential difference produced by the cell.

Question 14

(Triple only) What is a battery?

Answer 14

Contains two or more cells connected in series to produce a greater voltage.

Question 15

(Triple only) What are non-rechargeable batteries?

Answer 15

In alkaline batteries, at some point, the reactants in the batteries run out and no more electricity is produced and there is no way that we can reverse these reactions.

Question 16

(Triple only) Why can we recharge rechargeable batteries?

Answer 16

Because we can reverse the chemical reactions when we apply an electrical current.

Question 17

(Triple only) What is a fuel cell?

Answer 17

A cell that uses a chemical reaction to produce electricity and eventually the reactants are used up and the electricity stops.

Question 18

(Triple only) What are the advantages of Hydrogen fuel cells compared to rechargeable batteries?

Answer 18

-Hydrogen fuel cells will produce electricity for as long as you provide hydrogen whereas Rechargeable batteries run out and need to be recharged.

-Hydrogen fuel cells do not get less efficient the longer they run whereas Rechargeable batteries can store less electricity the more charging cycles they go through and eventually need to be replaced.

-Hydrogen fuel cells can also be a source of drinkable water e.g. on a space craft.

Question 19

(Triple only) What are the disadvantages of Hydrogen fuel cells compared to rechargeable batteries?

Answer 19

-Hydrogen fuel cells run on hydrogen which is an explosive gas and is very difficult to store safely whereas in Rechargeable batteries there are no dangerous fuels required however some rechargeable batteries can catch on fire if not manufactured correctly.

-Hydrogen fuel cells produce a relatively low potential difference or voltage so several are needed together whereas Rechargeable batteries can produce a greater potential difference than a hydrogen fuel cell.