C7 Energy changes

Question 1

What are exothermic reactions?

Answer 1

Reactions that transfer energy to the surroundings

Question 2

What are endothermic reactions?

Answer 2

Reactions that take in energy from the surroundings

Question 3

Examples of exothermic reactions (3)

Answer 3

Combustion, oxidation reactions - like respiration, neutralisation reactions

Question 4

What can exothermic reactions be used for?

Answer 4

To heat things up

Question 5

What can endothermic reactions be used for?

Answer 5

To cool things down

Question 6

How do cold packs work?

Answer 6

Water and ammonium nitrate are kept separate, when they mix the ammonium nitrate dissolves and takes in energy from the surroundings

Question 7

Explain the reaction profile for an exothermic reaction

Answer 7

The products are at a lower energy level than the reactants. This means when the reactants form the products, energy is released into the surroundings - heating them up

Question 8

Explain the reaction profile for an endothermic reaction

Answer 8

The products are at a higher energy level than the reactants. This means when the reactants form the products, energy is taken in from the surroundings - making them colder

Question 9

What is activation energy?

Answer 9

The minimum energy needed for the reaction to happen

Question 10

Is breaking bonds exothermic or endothermic?

Answer 10

Endothermic

Question 11

Is making bonds exothermic or endothermic?

Answer 11

Exothermic

Question 12

How do you calculate the energy changes in a reaction?

Answer 12

1. calculate the total energy needed to break all of the bonds in the reactants
2. calculate the total energy released in making all of the bonds in the products
3. calculate the difference between the two totals

Question 13

If the energy needed to break the bonds is more than the energy released when making the bonds, is the reaction exothermic or endothermic?

Answer 13

Endothermic

Question 14

If the energy released when making the bonds is more than the energy needed to break the bonds, is the reaction exothermic or endothermic?

Answer 14

Exothermic

Question 15

How do you make a cell?

Answer 15

Join two metals together using a wire and dip it in salt solution

Question 16

What effect does the difference is reactivity between the two metals used to create a cell have on the voltage?

Answer 16

The greater the difference, the higher the voltage produced

Question 17

What is the half equation at the negative electrode in a fuel cell?

Answer 17

2H2 + 4OH- > 4H2O +4e-

Question 18

What is the half equation at the positive electrode in a fuel cell?

Answer 18

O2 +2H2O + 4e- > 4OH-

Question 19

What are the advantages of hydrogen fuel cells? (3)

Answer 19

Do not need to be electrically recharged, no pollutants produced, can be a range of sizes for different uses

Question 20

What are the disadvantages of hydrogen fuel cells? (3)

Answer 20

Highly flammable, difficult to store, can be produced by non-renewable sources