Energy Changes

Question 1

Exothermic Reaction

Answer 1

Energy is released into the surroundings, bonds are formed

Question 2

Endothermic Reaction

Answer 2

Energy is taken in from the surroundings, bonds are broken

Question 3

Activation Energy

Answer 3

The minimum amount of energy needed for a reaction to take place

Question 4

Bond Energies

Answer 4

The amount of energy required to break one mole of a particular covalent bond

Question 5

Bond Forming
Exothermic or Endothermic?
Why?

Answer 5

Bond forming is exothermic as it releases energy to the surroundings

Question 6

Bond Breaking
Exdothermic or Endothermic?
Why?

Answer 6

Bond breaking is endothermic as it requires energy from the surroundings

Question 7

In bond energies calculations, exothermic reactions give what?

Answer 7

A negative number

Question 8

In bond energies calculations, endothermic reactions give what?

Answer 8

A positive number

Question 9

Electrolyte

Answer 9

A substance that can conduct electric current when molten or in solution

Question 10

Electrolysis

Answer 10

The decomposition of a compound using an electric current

Question 11

How do cells produce energy?

Answer 11

Through chemical reactions

Question 12

Battery

Answer 12

2 or more cells connected in series to produce a greater voltage

Question 13

What factors affect voltage in a cell/battery?

Answer 13

• Metals used for electrodes - the greater the difference in reactivity of the 2 metals, the greater the voltage
• The concentration of the electrolyte
• Conditions, e.g. temperature

Question 14

Rechargeable Cell/Battery

Answer 14

A cell/ battery where the reactions within it are reversible when an external current is applied

Question 15

Non Rechargeable Cell/Battery

Answer 15

A cell/battery where voltage is produced until one of the reactants is used up

Question 16

In a fuel cell, is the cathode positive or negative?

Answer 16

Positive

Question 17

In a fuel cell, is the anode positive or negative?

Answer 17

Negative

Question 18

How does a hydrogen fuel cell work

Answer 18

• Hydrogen enters the cell, is attracted to the negative electrode and is oxidised (loses electrons) to become e- and H+ ions
• e- ions travel through a wire to the cathode, H+ ions travel through electrolyte
• At the cathode, 4e- ions and 4h+ ions react with O2 to create water
• Water leaves fuel cell

Question 19

Negative Electrode Fuel Cell Half Equation

Answer 19

H2 –> 2e- + H+

Question 20

Positive Electrode Fuel Cell Equation

Answer 20

O2 + 4e- + 4H+ –> 2H2O

Question 21

Overall Fuel Cell Equation

Answer 21

O2 + 2H2 –> 2H2O

Question 22

How do hydrogen fuel cells generate electricity?

Answer 22

• Fuel (hydrogen) enters cell
• Hydrogen is oxidised (loses electrons)
• This sets up potential difference across the cell that drives the electrons around it generating electrical energy

Question 23

Pros of Hydrogen Fuel Cells

Answer 23

• Easy to maintain as there are no moving parts
• Small size
• Water is the only chemical product
• Last longer than batteries
• Reactants are abundant

Question 24

Cons of Hydrogen Fuel Cells

Answer 24

• Very expensive to manufacture
• Need a constant supply of hydrogen fuel, which is a flammable gas
• Hydrogen takes up storage space

Question 25

Do exothermic reactions create temperature increase or decrease?

Answer 25

Temperature increase

Question 26

Do endothermic reactions create temperature increase or decrease?

Answer 26

Temperature Decrease