Chapter 21: Fuels and Heats of Reaction

Question 1

Organic Chemistry

Answer 1

Is the study of the compounds of carbon

Question 2

Hydrocarbon

Answer 2

A compound that contains hydrogen and carbon only

Question 3

Fossil fuels

Answer 3

Are fuels that were formed from the remains of plants and animals that lived millions of years ago.

Question 4

Saturated compound

Answer 4

A saturated compound is one in which there are only single bonds between the atoms in the molecule.

Question 5

A homologous series

Answer 5

is defined as;
- A series of compounds of similar chemical properties
- Showing gradation in physical properties
- Having a general formula for its members
- Each member having a similar method of preparation
- Each member differing from the previous member by a CH2 unit.

Question 6

Structural Isomers

Answer 6

are compounds with the same molecular formula but different structural formulas.

Question 7

Unsaturated compound

Answer 7

An unsaturated compound is one that contains one or more double or triple bonds between the atoms in the molecule.

Question 8

An aliphatic compound

Answer 8

is an organic compound that consists of open chains of carbon atoms and closed chain compounds that resemble them in chemical properties.

Question 9

Aromatic compounds

Answer 9

are compounds that contain a benzene ring structure in their molecules

Question 10

Auto-ignition

Answer 10

is premature ignition of the petrol-air mixture before normal ignition of the mixture by a spark takes place.

Question 11

Sources of hydrocarbons;

Answer 11

• Coal
• Natural gas (methane)
• Petroleum (crude oil)

Question 12

Alkane formula

Answer 12

Cn H2n + 2

Question 13

Alkene formula

Answer 13

Cn H2n

Question 14

Alkyne formula

Answer 14

Cn H2n - 2

Question 15

Fractional Distillation process

Answer 15

1) Crude oil is heated in a furnace.
2) Hot crude oil mixture enters the bottom of the fractionating column which contains a series of trays to collect the condensed liquid.
3) Substances with higher boiling points condense in the lower part of the fractionating column.
4) Substances with lower boiling points condense in the higher part of the fractionating column.

Question 16

Octane Number

Answer 16

The octane number of a fuel is a measure of the tendency of the fuel to resist knocking.

Question 17

Factors affecting octane number

Answer 17

1) Length of chain: the shorter the alkane chain, the higher the octane number.
2) Degree of branching: the more branched the chain, the higher the octane number.
3) Straight chain or cyclic structure: Cyclic compounds have a higher octane number than straight chain compounds.

Question 18

Ways of increasing the octane number of petrol

Answer 18

1. Isomerisation
2. Catalytic cracking
3. Dehydrocyclisation
4. Adding oxygenates

Question 19

Catalytic cracking

Answer 19

is the breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short-chain molecules for which there is greater demand.

Question 20

Heat of reaction

Answer 20

is the heat change when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely.

Question 21

Heat of combustion

Answer 21

The heat of combustion of a substance is the heat change when one mole of the substance is completely burned in excess oxygen.

Question 22

Bond energy

Answer 22

the average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other.

Question 23

Heat of neutralisation

Answer 23

is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base.

Question 24

Heat of formation

Answer 24

The heat of formation of a compound is the heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states.

Question 25

Hess’s law

Answer 25

states that if a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction is carried out in one stage.

Question 26

The law of conservation of energy

Answer 26

states that energy cannot be created or destroyed but can only be converted from one form of energy into another.