C5 - Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

A reaction where energy is transferred to the surroundings. So the surrounding temperature increases.

Question 2

Give examples of exothermic reactions.

Answer 2

combustion
respiration
many neutralisation reactions

Question 3

What is an endothermic reaction?

Answer 3

A reaction where energy is transferred from the surroundings. So the surrounding temperature decreases.

Question 4

Give examples of endothermic reactions.

Answer 4

• thermal decomposition reactions
• the reaction between citric acid sodium hydrogen carbonate
• photosynthesis

Question 5

What is the activation energy?

Answer 5

The minimum energy needed to break bonds to start a reaction.

Question 6

If the reactants have more energy than the products, what kind of a reaction must have taken place?

Answer 6

An exothermic one. Energy has been transferred to the surroundings.

Question 7

If the reactants have less energy than the products, what kind of a reaction must have taken place?

Answer 7

An endothermic one. Energy has been taken in from the surroundings.

Question 8

Is breaking bonds endothermic or exothermic?

Answer 8

Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other)

Question 9

Is making bonds endothermic or exothermic?

Answer 9

Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy)

Question 10

How do we work out the energy change from a reaction profile?

Answer 10

The difference between the energy of the reactants and the energy of the products

Question 11

What is the collision theory?

Answer 11

Collisions between reacting particles are needed for chemical reactions to take place. These collisions must have sufficient energy (the activation energy).

Question 12

What is the conservation of energy principle?

Answer 12

Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as it was before the reaction.

Question 13

What is a reaction profile?

Answer 13

A graph which shows the relative energies of the reactants and products, as well as the activation energy of the reaction.

Question 14

What occurs in a chemical reaction in terms of bond energies?

Answer 14

Energy is absorbed to break bonds. Energy is released when bonds are formed.

Question 15

Describe exothermic and endothermic reaction in terms of bonds breaking/forming.

Answer 15

Endothermic - energy that is absorbed to break bonds is greater than what is released to make bonds
Exothermic - energy that is released to make bonds is greater than what is absorbed to break bonds

Question 16

What is a cell?

Answer 16

A cell is composed of two electrodes dipped in an electrolyte solution. It produces current from a chemical reaction.

Question 17

What is a battery?

Answer 17

Two or more cells connected in series.

Question 18

What determines the voltage obtained from a cell?

Answer 18

Identities of metals used as electrodes.
Concentration and identity of electrolyte.
Temperature of electrolyte.

Question 19

Explain rechargeable batteries.

Answer 19

Chemical reactions are reversed when external current is supplied.

Question 20

Explain non-rechargeable batteries.

Answer 20

All reactants are used up, cannot be recharged.

Question 21

What is a fuel cell?

Answer 21

Fuel cells consist of fuel and oxygen. Where the fuel is oxidised to produce electricity.

Question 22

What is a hydrogen fuel cell?

Answer 22

Where hydrogen is oxidised to form water.

Question 23

Why should batteries not be put in household waste?

Answer 23

Alkaline waste can be harmful / toxic / corrosive.

Question 24

What are the adv. of alkaline cells?

Answer 24

Cheap to manufacture.

Question 25

What are the disadvantages of alkaline cells?

Answer 25

Expensive to recycle.
Toxic waste.
May end up in landfill sites.