Energy Changes

Question 1

Exothermic reactions

Answer 1

When the reaction transfers energy to its surroundings

Question 2

Examples of exothermic reactions

Answer 2

Combustion, respiration, neutralisation

Question 3

Why is energy transferred in a reaction

Answer 3

Bonds are broken and bonds are made

Question 4

Examples of endothermic reactions

Answer 4

Ice-packs
Eating sherbet

Question 5

Activation energy

Answer 5

The miniumum amount of energy for a reaction to take place

Question 6

What are bond energy measured in

Answer 6

KJ/mol

Question 7

In endothermic bonds are

Answer 7

Broken

Question 8

In an exothermic reaction the potential energy at the end

Answer 8

Is less- gives out energy

Question 9

In an endothermic reaction the potential energy at the end

Answer 9

Is more- takes in energy

Question 10

What is enthalpy change

Answer 10

Energy change

Question 11

How to calculate the energy changes in a reaction using bonds

Answer 11

1. Write symbol equation and workout the bonds breaking and the bonds being made
2. Use the bond energy values provided to workout the energy value of all of the bonds of the reactants
3. Workout the value of how much energy is required to form the bonds of the products
4. Do the sum of the energy of the bonds broken minus the sum of the energy of the bonds made

Question 11

How would you affect the temperature changes in reacting solutions

Answer 11

1. Place polystyrene cup inside of beakers
2. Use measuring cylinder to measure 30cm3 of acid and pour into polystyrene
3. Record the temperature of the acid
4. Use a strip of metal e.g. magnesium
5. Add the solid to the acid and record temp every 10 mins

Question 12

What does a chemical cell do and what are the 2 types

Answer 12

Convert chemical energy into electrical energy
Rechargeable and non-rechargeable cell

Question 13

How do non-rechargeable cells work

Answer 13

Produce a voltage until the chemical substances are used up

Question 14

How do rechargeable cells work

Answer 14

An electrical current is passed through the cell backwards. The chemical reaction is reversed so a voltage can be produced again

Question 15

how do fuel cells work

Answer 15

Hydrogen is oxidized electrochemically
Fuel is not combusted
Only product is water

Question 16

What is the voltage of the cell affected by

Answer 16

The bigger the difference of the reactivity of the metals
Reactivity series

Question 17

What are the redox in a fuel cell

Answer 17

Oxygen is reduced
Hydrogen is oxidised

Question 18

Ionic equations in fuel cell

Answer 18

2H2 + O2 –> 2H20

Question 19

Half equations in a fuel cell at cathode and at anode

Answer 19

2H2 + 4OH- —> 4H2O + 4e-
O2 + 2H2O + 4e- —> 4OH-