Energy Changes (5)

Question 1

What is the conservation of energy principle?

Answer 1

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

Question 2

What is an exothermic reaction?

Answer 2

A reaction where energy is transferred to the surroundings so that the surroundings temperature increases

Question 3

What is an example of an exothermic reaction

Answer 3

combustion, oxidation reactions and neutralisation (acid + alkali) reactions. Negative sign of energy change.

Question 4

What is an endothermic reaction?

Answer 4

A reaction where energy is taken in from the surroundings so the surroundings temperature decreases

Question 5

What is an example of an endothermic reaction?

Answer 5

Melting ice cubes.

Melting solid salts.

Evaporating liquid water.

Question 6

What is activation energy?

Answer 6

Minimum amount of energy that particles need to react

Question 7

What is a reaction profile?

Answer 7

Reaction profile is a graph which shows the relative energies of reactants and product, as well as activation energy of the reaction.

Question 8

What occurs in a chemical reaction in
terms of bond energies? Describe exothermic and endothermic reactions in terms of bond breaking/forming.

Answer 8

Bond breaking is an endothermic process, because it requires energy.

Bond forming is an exothermic process, because it releases energy.

Question 9

What is the equation to find enthalpy change in terms of bond energies?

Answer 9

Energy of reaction = sum of bonds broken – sum of bonds made

Question 10

What is a cell?

Answer 10

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

Question 11

What is a battery?

Answer 11

A battery consists of two or more cells connected in series.

Question 12

What determines the voltage obtained from a cell?

Answer 12

Identities of metals used as electrodes and the identity and concentration of an electrolyte.

Question 13

State the advantages of using cells and batteries.

Answer 13

(+) more or less cheap, some are rechargeable, a convenient source of electrical energy

Question 14

State the disadvantages of using cells and batteries.

Answer 14

(-) harmful chemicals

Question 15

Describe rechargeable cells

Answer 15

Rechargeable – chemical reactions are reversed when an external current is supplied

Question 16

Describe non-rechargeable cells

Answer 16

Non-rechargeable – reactants are used up, cannot be recharged

Question 17

What is a fuel cell?

Answer 17

Fuel cells are supplied by fuel and oxygen to oxidise the fuel to generate electricity.

Question 18

What is the overall reaction in a hydrogen fuel cell? What are the half equations?

Answer 18

Question 19

What are the advantages of fuel cells

Answer 19

Advantages: no pollutants, no recharging

Question 20

What are the disadvantages of hydrogen fuel cells?

Answer 20

Question 21

What is 🔺(delta)H

Answer 21

Overall energy change

Question 22

What is -🔺(delta)H

Answer 22

Exothermic (hot)

Question 23

What is +🔺(delta)H

Answer 23

Endothermic feels cold

Question 24

.

Answer 24

.

Question 25

What is overal energy change

Answer 25

The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed

Question 26

.

Question 27

.

Answer 27

.

Question 28

What has more energy reactants or products in a exothermic reaction

Answer 28

reactants

Question 29

What has more energy reactants or products in a endothermic reaction

Answer 29

products

Question 30

Draw a sketch of a exothermic reaction

Answer 30

Question 31

Draw a sketch of a endothermic reaction

Answer 31