Seneca C5

Question 1

What are Exothermic Reactions

Answer 1

Energy from the reacting chemicals is transferred to the surroundings, which often increase in temperature as a result

Question 2

What are examples of Exothermic Reactions

Answer 2

Combustion.
Neutralization.
Oxidation.

Question 3

What are Endothermic Reactions

Answer 3

Energy from the surroundings is transferred to the reacting chemicals, causing the temperature of the surroundings to decrease

Question 4

What are examples of Endothermic Reactions

Answer 4

Thermal decomposition.
The reaction that happens when citric acid is combined with sodium hydrogen carbonate (sodium bicarbonate).

Question 5

What are the 2 main requirements for a successful reaction to take place

Answer 5

. Collisions
. Activation Energy

Question 6

What is activation energy

Answer 6

The activation energy is the minimum amount of energy that reacting particles must have for a reaction to happen.

Question 7

What do reaction profiles tell us

Answer 7

. The amount of energy contained within the reactants and the products.
. The activation energy of a reaction.
. The overall energy change that happens as a result of a reaction.

Question 8

How can catalysts increase reaction rates

Answer 8

. By lowering the activation energy

Question 9

What is bond energy

Answer 9

All chemical bonds have a “bond energy” that measures the strength of chemical bonds

Question 10

How can we see if a reaction is exothermic or endothermic (bond energy)

Answer 10

By subtracting the total bond energies of the products from the total bond energies of reactants, we can see if a reaction is endothermic or exothermic

Question 11

Exothermic reactions (bond energy)

Answer 11

Energy released by making bonds > energy required to break bonds

Question 12

Endothermic reactions (bond energy)

Answer 12

Energy released by making bonds < energy required to break bonds

Question 13

Bond breaking

Answer 13

Bond breaking requires energy and thus is an endothermic process

Question 14

Bond making

Answer 14

Bond making releases energy and thus is an exothermic process

Question 15

Bond energy

Answer 15

This is a measure of the strength of chemical bonds. The units are kilojoules per mole (kJ/mol)

Question 16

How do we make a simple cell

Answer 16

We can make a simple cell by connecting 2 different electrodes and putting them in a liquid electrolyte
The difference in the reactivity of the metals produces a voltage

Question 17

How do we change the voltage output of a cell

Answer 17

. Changing the type of electrode
. Changing the type of electrolyte
. Changing both

Question 18

Changing the type of electrode

Answer 18

A greater difference in reactivity between the two electrodes will result in the cell having a greater voltage

Question 19

Changing the type of electrolyte

Answer 19

Changing the electrolyte changes the reactions that happen at the electrodes. This will result in the voltage output of the cell changing.

Question 20

In a chemical cell, what effect will increasing the difference in reactivity between the two electrodes have on voltage output?

Answer 20

Increasing voltage output

Question 21

In a chemical cell, what effect will decreasing the difference in reactivity between the two electrodes have on voltage output?

Answer 21

Decreasing voltage output

Question 22

What is a battery

Answer 22

A battery is a collection of more than one cell joined in series (end-to-end).

Question 23

How is the voltage of a battery calculated

Answer 23

The voltage of a battery is calculated as the sum of the voltages of its individual cell components.

Question 24

What happens when the chemicals inside a battery run out

Answer 24

When the chemicals in a battery run out, the battery can not be used anymore.

Question 25

A battery that has a voltage output of 9V is made up of 3 identical cells. What is the voltage output of each of its individual cell components?

Answer 25

3V

Question 26

Rechargeable cells/ batteries

Answer 26

In rechargeable cells and batteries, connection to an electric current reverses the reactions that happen at the electrodes.

This means that electricity can continue to be produced as long as there is access to this external electric current.

Question 27

Non - rechargeable cells/ batteries

Answer 27

In non-rechargeable cells and batteries (e.g. alkaline batteries), irreversible reactions take place at the electrodes.
This means that electricity can no longer be produced as soon as one of the reacting chemicals has run out.

Question 28

How are cells connected together in batteries?

Answer 28

In series

Question 29

What are the advantages of fuel cells

Answer 29

. Reliable
. High efficiency
. Less pollution
. Compact and lightweight

Question 30

The reaction of fuel cells

Answer 30

The reaction is between an external fuel source and oxygen. Once added to the cell, the fuel is oxidized, and this causes a voltage to be established.

Question 31

What is the waste product of hydrogen fuel cells

Answer 31

In hydrogen fuel cells, the oxidation of hydrogen generates a voltage and the only waste product is water

Question 32

What is the overall equation for a hydrogen fuel cell?

Answer 32

2H2 + O2 → 2H2O

Question 33

What are the risks of hydrogen fuel cells

Answer 33

. Hydrogen has to be stored at a high pressure and hydrogen gas is explosive

Question 34

Why are hydrogen fuel cells better than rechargeable batteries and cells

Answer 34

. Less toxic
. Higher lifetime
. Higher capacity

Question 35

Why are fuel cells reliable

Answer 35

They don’t have any moving parts