Energy Changes

Question 1

In an exothermic reaction is heat transferred to or from the surroundings

Answer 1

To the surroundings

Question 2

Name two different types of reaction which are exothermic

Answer 2

• Combustion

- Neutralisation

Question 3

Define what is meant by an endothermic reaction

Answer 3

An endothermic reaction is one which takes in energy from the surroundings.

Question 4

Write down the equation for the thermal decomposition of calcium carbonate

Answer 4

CaCO3 (+heat) –> CO2 + CaO

Question 5

What is the purpose of putting the reaction container into a beaker containing cotton wool during an experiment to investigate the temperature change of an exothermic reaction

Answer 5

To provide insulation so that energy is not lost to the surroundings

Question 6

What is the activation energy of a reaction

Answer 6

The minimum amount of energy the reactants need to collide with each other and react.

Question 7

In an endothermic reaction do the products of the reaction have more or less energy than the reactants

Answer 7

The products have more energy than the reactants

Question 8

What type of process is bond breaking

Answer 8

Endothermic

Question 9

What type of process is bond forming

Answer 9

Exothermic

Question 10

In what type of reaction is the energy released by forming bonds greater than the energy used to break them

Answer 10

Exothermic

Question 11

What three steps would you use to find the overall energy change in a reaction if you were given the known bond enthalpies for the bonds present in the reactants and products

Answer 11

• Find the energy required to break the original bonds
• Find the energy released by forming the new bonds
• Find the overall energy change by subtracting energy released by forming bonds by energy required to break bonds

Question 12

What is an electrolyte in an electrochemical cell

Answer 12

A liquid that contains ions which react with the electodes

Question 13

Give two factors that affect the voltage produced by an electrochemical cell

Answer 13

• Types of electrodes used, the bigger the difference in reactivity of electrodes the bigger the voltage of the cell
• THe electrolyte used in a cell as different ions in solution will react differently with the metal electrodes used

Question 14

What is a battery

Answer 14

Formed by connecting two or more cells together in series. The voltages of the cells in the battery are combined so there is a bigger voltage overall.

Question 15

Explain why non-rechargeable batteries eventually lose their charge

Answer 15

In some cells the chemical reactions that happen at the electrodes are irreversible so over time the reacting particles get used up therefore the reaction can’t happen

Question 16

What is a fuel cell

Answer 16

An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy

Question 17

Name an electrolyte commonly used in hydrogen oxygen fuel cells

Answer 17

Potassium hydroxide

Question 18

In a hydrogen oxygen fuel cell which molecule becomes oxidised and which becomes reduced

Answer 18

Hydrogen loses electrons to produce H+ ions and becomes oxidised
Oxygen gains electrons from the cathode and reacts with H+ ions to make water, it gets reduced

Question 19

Write down the overall equation for the reaction in hydrogen oxygen fuel cells

Answer 19

2H2 + O2 –> 2H2O

Question 20

Why is the reaction that takes place in a hydrogen oxygen fuel cell described as a redox reaction

Answer 20

Because there is reduction at the cathode an oxidation at the anode

Question 21

State 3 advantages of hydrogen oxygen fuel cell powered cars over battery powered electrical cars

Answer 21

• Don’t produced as many pollutants as batteries are more polluting to dispose off
• There is a limit to how many times batteries can be recharged.
• Batteries store less energy than fuel cells
• Batteries are more expensive to make than fuel cells

Question 22

Describe how a hydrogen oxygen fuel cell works

Answer 22

Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment . At the anode hydrogen is oxidised to produce H+ ions and the H+ ions in the electrolyte move to the cathode. At the cathode oxygen is reduced and reacts with H+ ions to make water. The electrons flow through an external circuit from the anode to the cathode, which is the electric current