Energy Chnages

Question 1

Exothermic reactions

Answer 1

Transfers energy to the surroundings so temperature of the surroundings increases
-> products have less energy than reactants

Examples: combustion, oxidation, neutralisation

Question 2

Endothermic reactions

Answer 2

Takes energy in from the surroundings so that temperature if the surroundings decreases
-> products have more energy than reactants

Examples: thermal decomposition

Question 3

Activation energy

Answer 3

The minimum energy required for a reaction to take place

Question 4

Energy changes in reactions (in relation to bonds)

Answer 4

• energy must be supplied to break bonds in the reactants
• energy is released when bonds in the products are formed

Question 5

Endothermic reactions (in relation to bonds)

Answer 5

More energy is needed to break bonds than is released forming new bonds

Question 6

Exothermic reactions (in relation to bonds)

Answer 6

More energy is released forming new bonds than is needed to break bonds

Question 7

Cells

Answer 7

Contain chemicals which react to produce electricity

Question 8

What does voltage depend on

Answer 8

Type of electrode and electrolyte

Question 9

Battery

Answer 9

2 or more cells connected together in a series to provide a greater voltage

Question 10

Non-rechargeable cells and batteries

Answer 10

• chemical reactions stop when one of the reactants is used up
• alkaline batteries are non-rechargeable

Question 11

Rechargeable cells and batteries

Answer 11

• can be recharged because the reactions are reversible when an electrical current is supplied

Question 12

Bro jsut talk about Fuel cells idk
How about u spell just right bro

Answer 12

• supplied by an external source of fuel (eg hydrogen) and oxygen
• the fuel is electrochemically oxidised in the cell to produce a p.d.
• involves the oxidation of hydrogen to produce water

Question 13

Half equations for hydrogen fuels cells

Answer 13

Anode (-):
2H2 (g) -> 4e- + 4H+ (g)

Cathode (+):
4H+ (g) + O2 (g) + 4e- -> 2H2O (l)

Question 14

Overall equation for hydrogen fuel cells

Answer 14

2H2 + O2→ 2H2O

Question 15

Advantages and disadvantages of hydrogen fuel cells

Answer 15

Advantages
- They do not produce any pollution (only waste product is water)
- They produce more energy per kilogram than either petrol or diesel
- No batteries to dispose of which is better for the environment
- Continuous process and will keep producing energy as long as fuel is supplied

Disadvantages
- High pressure tanks are needed to store the oxygen and hydrogen in sufficient amounts which are dangerous and difficult to handle (explosive)
- Hydrogen is expensive to produce and store

Question 16

Why does temp go up when acid is added in Calorimetry practicals

Answer 16

Because it is an exothermic reaction