Unit 5- Energy Changes

Question 1

What is an Exothermic reaction

Answer 1

One which transfers energy to the surroundings usually by heating. This is shown as a rise in temperature

Question 2

What is an endothermic reaction

Answer 2

Reactions which takes energy in from the surroundings, this is shown as a fall in temperature

Question 3

Example of Exothermic reaction

Answer 3

Neutralisation, combustion

Question 4

Uses of Exothermic reactions

Answer 4

Hand warmers- use the Exothermic oxidation of iron in air to release energy
Self heating cans

Question 5

Example of endothermic reaction

Answer 5

Thermal decomposition

Question 6

Uses of endothermic reactions

Answer 6

Used in sport injury packs, allows pack to become instantly cooler without having to be put in freezer

Question 7

What is a fuel cell

Answer 7

Electrical cell that produces electricity using fuel and oxygen

Question 8

Uses of fuel cells

Answer 8

Used in vehicles- don’t produce nasty pollutants, however uses a lot of energy

Question 9

What is the voltage in a cell dependant on

Answer 9

Type of electrode and electrolyte

Question 10

Advantages and disadvantages of hydrogen fuel cells

Answer 10

Produce electricity as long as they are supplied with fuel (hydrogen) inline batteries that will eventually run out
Only by product is water
Clean alternative (environmentally friendly)

More expensive
Hydrogen flammable so careful handling and storage

Question 11

Advantages + disadvantages of rechargeable cells (batteries)

Answer 11

-ideal for portable devices
-Less expsive than hydrogen fuel cell
-Easy to use

-limited range need to be reachrged
-environmental impacts when disposing of

Question 12

At the anode hydrogen fuel cells half equation - remember anode is the negative electrode in hydrogen fuel cells

Answer 12

Oxidation of hydrogen :
2H2 —> 4H+ + 4e

Question 13

How hydrogen fuel cells work

Answer 13

1. Hydrogen comes in from the leftoutlet and is oxidised by the anode
2. Hydrogen atom loses an e,et rom to be come H+ ions
3. Hydrogen ions move over the electrolyte to the cathode
4. They then react to make water (reduced)

Question 14

At the cathode hydrogen fuel cells half equations- remember the cathode is positive as it is the other way around

Answer 14

O2 + 4H+ +4e- —> 2H2O

Question 15

Overall hydrogen fuel cell equation

Answer 15

2H2 + O2 —> 2H2O