Energy Changes

Question 1

What is the law of conservation of energy?

Answer 1

Energy cannot be created or destroyed, only transferred.

Question 2

What happens to the temperature during an exothermic reaction?

Answer 2

The temperature increases.

Question 3

Give two examples of exothermic reactions.

Answer 3

• Neutralisation
• Combustion

Question 4

What is an endothermic reaction?

Answer 4

An endothermic reaction takes heat energy in.

Question 5

What is a typical example of an endothermic reaction?

Answer 5

• Electrolysis
• Thermal decomposition
• First stages of photosynthesis
• Reaction between citric acid and sodium hydrogencarbonate

Question 6

What is the effect of an endothermic reaction on temperature?

Answer 6

The temperature decreases.

Question 7

What do neutralisation reactions typically do?

Answer 7

They always give energy out.

Question 8

What is activation energy (Ea)?

Answer 8

The minimum amount of energy required for a collision to be successful in a chemical reaction.

Question 9

What does an energy profile diagram represent?

Answer 9

The relative energies of the reactants and products in a chemical reaction.

Question 10

In an exothermic reaction, how does the energy of the products compare to the reactants?

Answer 10

The energy of the products is lower than the energy of the reactants.

Question 11

How is energy change represented in an exothermic reaction profile?

Answer 11

With a downwards pointing arrow.

Question 12

What is bond breaking and is it endothermic or exothermic?

Answer 12

Bond breaking is an endothermic process.

Question 13

What is bond making and is it endothermic or exothermic?

Answer 13

Bond making is an exothermic process.

Question 14

When is a reaction considered endothermic?

Answer 14

If more energy is absorbed than is released.

Question 15

What is the energy change formula?

Answer 15

Energy change = Energy taken in - Energy given out.

Question 16

What does a negative energy change indicate about a reaction?

Answer 16

Energy is being released to the surroundings, indicating an exothermic reaction.

Question 17

What type of reaction occurs if more energy is released than absorbed?

Answer 17

An exothermic reaction.

Question 18

What is the significance of bond energies in a chemical reaction?

Answer 18

They determine how much energy is required to break bonds or released when bonds are formed.

Question 19

What is the purpose of a calorimetry study?

Answer 19

To investigate temperature changes during a chemical reaction.

Question 20

What materials are needed for the calorimetry study of HCl and NaOH?

Answer 20

• Dilute hydrochloric acid
• Dilute sodium hydroxide solution
• Styrofoam calorimeter
• 25 cm3 measuring cylinder
• Thermometer
• Stirrer

Question 21

What is the expected outcome of the calorimetry study regarding temperature?

Answer 21

The temperature change will vary depending on the amounts of solutions involved.

Question 22

In a reaction profile diagram, what does a reaction with a positive energy change indicate?

Answer 22

It is an endothermic reaction.

Question 23

What is the result of the reaction if the energy change is positive?

Answer 23

The products have more energy than the reactants.

Question 24

What is a chemical cell?

Answer 24

A source of electrical energy consisting of two electrodes made from metals of different reactivity immersed in an electrolyte

Question 25

What is the simplest design of a chemical cell?

Answer 25

Two electrodes connected to an external voltmeter by wire, creating a complete circuit

Question 26

Which metals are commonly used in a basic chemical cell?

Answer 26

Zinc and copper

Question 27

Why does the more reactive electrode become negatively charged?

Answer 27

It readily releases electrons

Question 28

What determines the voltage produced by a chemical cell?

Answer 28

The difference in the ability of the electrodes to release electrons and the reactivity of the metals

Question 29

What effect does the electrolyte have on a chemical cell?

Answer 29

It affects the voltage as different ions react with the electrodes in different ways

Question 30

What is the difference between a cell and a battery?

Answer 30

A battery connects two or more cells in series to provide a larger overall voltage

Question 31

What happens to a battery when one of the reactants is used up?

Answer 31

The battery dies or goes flat

Question 32

What characterizes non-rechargeable batteries?

Answer 32

The reactions are irreversible, and the battery must be replaced once depleted

Question 33

How do rechargeable batteries differ from non-rechargeable ones?

Answer 33

Reactions are reversed by connecting to an external electrical supply, allowing the cycle to be repeated

Question 34

What is a hydrogen fuel cell?

Answer 34

An electrochemical cell where a fuel donates electrons at one electrode and oxygen gains electrons at the other

Question 35

What is produced in a hydrogen-oxygen fuel cell?

Answer 35

Energy and water

Question 36

What are the advantages of hydrogen fuel cells?

Answer 36

* They do not produce any pollution * They produce more energy per kilogram than petrol or diesel * No power is lost in transmission * Better for the environment due to no batteries to dispose of

Question 37

What are the disadvantages of hydrogen fuel cells?

Answer 37

* Materials used are expensive * High-pressure tanks are needed * Affected by low temperatures, becoming less efficient * Hydrogen is expensive to produce and store

Question 38

What is the role of the electrodes in a hydrogen fuel cell?

Answer 38

Hydrogen enters at the anode where it is oxidised and oxygen enters at the cathode where it is reduced

Question 39

What is the reaction that occurs at the anode of a hydrogen fuel cell?

Answer 39

2H2 → 4H+ + 4e–

Question 40

What is the reaction that occurs at the cathode of a hydrogen fuel cell?

Answer 40

4H+ + O2 + 4e– → 2H2O

Question 41

What is the overall reaction in a hydrogen fuel cell?

Answer 41

2H2 + O2 → 2H2O

Question 42

How are electrons used in a hydrogen fuel cell?

Answer 42

They move around the external circuit from the anode to the cathode to drive an electric motor

Question 43

What electrolyte is commonly used in hydrogen fuel cells?

Answer 43

Phosphoric acid

Question 44

Fill in the blank: In fuel cells, the anode is the _______ electrode and the cathode is the _______ electrode.

Answer 44

negative; positive