C7 - Energy changes

Question 1

What is an exothermic energy transfer?

Answer 1

Energy is transferred to the surroundings

Question 2

What happens to the surrounding temperature in an exothermic reaction?

Answer 2

It increases

Question 3

What are some uses of exothermic reactions?

Answer 3

Hand warmers, heating pads

Question 4

What is an endothermic energy transfer?

Answer 4

Energy is transferred from the surroundings

Question 5

What happens to the surrounding temperature in an endothermic reaction?

Answer 5

It decreases

Question 6

What are some uses of endothermic reactions?

Answer 6

Chemical cold packs

Question 7

What is a reaction profile?

Answer 7

A diagram showing the energy changes in a reaction

Question 8

What is the activation energy?

Answer 8

The minimum energy that will result in a reaction when particles collide

Question 9

What is bond energy?

Answer 9

The energy required to break a bond or the energy released when a bond is formed

Question 10

How do you calculate the overall energy used during a reaction?

Answer 10

Total bond energy used when breaking bonds - Total bond energy released when forming bonds

Question 11

In terms of bonds, what is an exothermic reaction?

Answer 11

Less energy is required to break bonds than is released to make them
It will be negative

Question 12

In terms of bonds, what is an endothermic reaction?

Answer 12

More energy is required to break bonds than is released to make them

Question 13

How are chemical cells made?

Answer 13

Connect two different metals (electrodes) in a solution (electrolyte)

Question 14

What is a battery?

Answer 14

Two or more cells connected in series

Question 15

How can the potential difference of a chemical cell be changed?

Answer 15

Connect two metals with a greater difference in reactivity to increase p.d.

Question 16

How can some cells be recharged?

Answer 16

By applying an external current

Question 17

Why can some cells not be recharged?

Answer 17

The reaction can’t be reversed

Question 18

What is a fuel cell?

Answer 18

A cell that uses a fuel and oxygen to generate electricity

Question 19

What is the overall equation for a hydrogen fuel cell?

Answer 19

2H2(g) + O2(g) —> 2H20(l)

Question 20

In acidic hydrogen fuel cells what are the half equations?

Answer 20

2H2(g) —> 4H+(aq) + 4e-

O2(g) + 4H+(aq) + 4e- —> 2H2O(l)

Question 21

What are some advantages of hydrogen fuel cells?

Answer 21

• The only product is water
• Doesn’t need to be electrically recharged

Question 22

What are some disadvantages of hydrogen fuel cells?

Answer 22

• Hydrogen is v. flammable
• Difficult to store - pressurised canisters
• Produced from non-renewable sources