Topic 5: Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

A reaction that transfers energy to the surroundings. This is shown by a rise in temperature

Question 2

Examples of exothermic reactions [3]

Answer 2

1. Combustion
2. Oxidation
3. Neutralisation

Question 3

Everyday uses of exothermic reactions [2]

Answer 3

1. Hand warmers
2. Self-heating cans (of coffee)

Question 4

What is an endothermic reaction?

Answer 4

A reaction that takes in energy from the surroudings. This is shown by a fall in temperature

Question 5

Examples of endothermic reactions [2]

Answer 5

1. Thermal decomposition
2. Reaction between citric acid and sodium hydrogencarbonate

Question 6

Everyday use of endothermic reactions

Answer 6

Sports injury packs

Question 7

What is activation energy?

Answer 7

The minimum amount of energy the reactant particles need in order to collide with each other and react

Question 8

Draw the reaction profile diagram for an exothermic reaction [4]

Answer 8

1. Axies correctly labelled
2. Reactants/products labelled
3. Activation energy labelled
4. Energy released labelled

Question 9

Draw the reaction profile diagram for an endothermic reaction [4]

Answer 9

1. Axies correctly labelled
2. Reactants/products labelled
3. Activation energy labelled
4. Energy absorbed labelled

Question 10

Is bond breaking endothermic or exothermic?

Answer 10

Endothermic

Question 11

Why is bond breaking endothermic?

Answer 11

Energy must be supplied to break existing bonds

Question 12

Is bond formation endothermic or exothermic?

Answer 12

Exothermic

Question 13

Why is bond formation exothermic?

Answer 13

Energy is released when new bonds are formed

Question 14

How do you calculate overall energy change in a bond equation?

Answer 14

energy required to break bonds - energy released by forming bonds

Question 15

What is bond energy?

Answer 15

The amount of energy required to break one mole of a particular covalent bond

Question 16

If a bond calculation gives a negative number, is the overall reaction exothermic or endothermic?

Answer 16

Exothermic (energy is being released)

Question 17

How can a cell use a chemical reaction to produce electricity?

Answer 17

A cell can be made by connecting two different electrodes with a wire, and placing them in contact with an electrolyte

Question 18

How can a cell voltage be measured?

Answer 18

Using a voltmeter

Question 19

What are batteries?

Answer 19

Two or more cells, connected in series, to create a greater voltage

Question 20

What factors affect the voltage of a cell? [3]

Answer 20

1. The metals used for the electrodes (greater the difference in reactivity, greater the voltage)
2. The type and conc. of electrolyte used
3. Conditions (such as temperature)

Question 21

Why can rechargeable batteries be recharged?

Answer 21

The chemical reactions are reversed when an external electrical current is supplied

Question 22

What uses rechargeable batteries? [2]

Answer 22

1. Phones
2. Laptops

Question 23

Why are some batteries non-rechargeable?

Answer 23

The chemical reactions stop when the reactants have been used up

Question 24

What uses non-rechargeable batteries? [2]

Answer 24

1. TV remotes
2. Smoke alarms

Question 25

Are alkaline batteries rechargeable?

Answer 25

No (non-rechargeable)