10.-Energy-Content-of-Fuels

Question 1

What is a fuel?

Answer 1

Most fuels are organic compounds containing carbon, hydrogen, and sometimes oxygen.

Question 2

What happens when a fuel is ignited?

Answer 2

It undergoes combustion.

Question 3

How do we obtain fuels from crude oil?

Answer 3

Crude oil is a mixture of substances made up mainly of hydrocarbons.

Question 4

What are the main hydrocarbons in crude oil?

Answer 4

Most of the hydrocarbons in crude oil are alkanes.

Question 5

What is fractional distillation?

Answer 5

Crude oil is separated into many useful fractions by the process of fractional distillation.

Question 6

What is the process of fractional distillation?

Answer 6

Heat crude oil into a vapour in a furnace, then pass vapour through a fractionating column.

Question 7

What happens as the length of the carbon chain increases?

Answer 7

Darker in colour, more viscous, less flammable, and sootiness of flame increases.

Question 8

What are alcohols in the context of fuels?

Answer 8

Alcohols are another homologous series of organic compounds.

Question 9

What is the general formula for alcohols?

Answer 9

C𝑛 H2𝑛+1 OH

Question 10

What are the first five alcohols?

Answer 10

Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Pentan-1-ol.

Question 11

How can methanol and ethanol be obtained?

Answer 11

They can be obtained from renewable energy sources.

Question 12

What is the chemical equation for ethanol combustion?

Answer 12

ethanol + oxygen → carbon dioxide + water

C2 H5 OH + 3O2 → 2CO2 + 3H2 O

Question 13

Why is the use of ethanol considered carbon neutral?

Answer 13

The CO2 produced is used for photosynthesis by the plants grown to produce the ethanol.

Question 14

What are the hazards associated with fuels?

Answer 14

Toxicity, flammability, and risk of explosion.

Question 15

What is an example of a toxic fuel?

Answer 15

Methanol can attack the central nervous system and may lead to blindness, coma, or death.

Question 16

What occurs during incomplete combustion?

Answer 16

Carbon monoxide gas and carbon can form, as well as carbon dioxide.

Question 17

What is carbon monoxide?

Answer 17

A toxic, colourless, and odourless gas that can lead to asphyxiation.

Question 18

What are particulates?

Answer 18

Soot formed when burning hydrocarbons that can cause respiratory problems.

Question 19

What is the effect of sulphur impurities in fossil fuels?

Answer 19

They react with oxygen to form sulphur dioxide, which can cause respiratory problems.

Question 20

What is the consequence of sulphur dioxide in the atmosphere?

Answer 20

It can produce sulfuric acid, leading to acid rain.

Question 21

What are the different units of energy?

Answer 21

Joules (J), kilojoules (kJ), calories (cal), kilocalories (kcal), and kilowatt-hours (kWh).

Question 22

What is the equation to find heat energy released by a fuel?

Answer 22

Heat energy = Mass of water × Specific heat capacity of water × Temperature rise of water.

Question 23

What is a bomb calorimeter?

Answer 23

An apparatus designed to reduce heat loss and ensure complete combustion.

Question 24

What happens when a fuel is burnt?

Answer 24

Energy is needed to break bonds in the reactants and released when new bonds form in the products.

Question 25

What is the heat energy released by the first five alcohols?

Answer 25

Methanol: 726 kJ mol-1, Ethanol: 1367 kJ mol-1, Propan-1-ol: 2017 kJ mol-1, Butan-1-ol: 2675 kJ mol-1, Pentan-1-ol: 3323 kJ mol-1.