C5 Energy Changes

Question 1

Activation energy

Answer 1

Minimum amount of energy needed for particles to react

Question 2

What occurs with energy when bonds are broken or formed

Answer 2

Bonds broken-Takes in energy in form of heat
Bonds formed-Releases energy in form of heat

Question 3

Draw the reaction profile for an exothermic reaction

Answer 3

Reactants higher than products.
Small arrow up for activation energy.
Large arrow down shows overall energy loss.

Question 4

Draw the reaction profile for an endothermic reaction

Answer 4

Reactants lower than prodcuts.
Activation energy long arrow just above products.
Energy absorbed goes up to products

Question 5

Exothermic
Endothermic

Answer 5

Exothermic-A reaction which transfers energy to surroundings usually in the form of heat.
Endothermic-A reaction in which it takes in energy from the surroundings. Shown by a fall temperature.

Question 6

2 examples of endothermic/Exothermic reactions

Answer 6

Endothermic- Citric acid+ Sodium hydrogencarbonate
Thermal decomposition

Exothermic-Combustion
Neutrilisation

Question 7

Definition

Fuel cell

Answer 7

An electrical cell that supplied with a fuel and oxygen

Question 8

How does a fuel cell work

Answer 8

The electrolyte is often an acid and the electrodes are often pouros carbon with a catalyst.
Hydrogen enters the anode(pos) compartment.
Oxygen enters cathode(neg) compartment

At the anode. Hydrogen loses electrons to produce H+ ions. This is oxidation.
H+ ions in electrolyte move to the cathode

At the cathode oxygen gains electrons from cathode and reacts with H+ ions to make water. This is called reduction.
Electrons flow through an external circuit from anode to the cathode. This is the electric current.
Overall reaction is hydrogen plus oxygen which gives water.

Question 9

3 Advantage/Disadvantages of fuel cells

Answer 9

Pros-Not many pollutants
Fuel cells store more energy than batteries
Fuel cells are easier to dispose of compared to batteries as they contain heavy metals

Cons-Hydrogen is a gas so takes up more space to store than battery
Explosive when mixed with air so hard to store
Hydrogen fuel is either made from hydrocarbons or electroloysis which uses electricity or fossil fuels