2.5 Hydrocarbons

Question 1

What are the only products when a hydrocarbon fuel undergoes complete combustion?

Answer 1

Water (H(2)O) and carbon dioxide (CO(2)).

Question 2

Write a balanced chemical equation for the complete combustion of ethane

Answer 2

2C(2)H(6) + 7O(2) → 4CO(2) + 6H(2)O

Question 3

When does incomplete combustion occur? What is required to ensure complete combustion occurs?

Answer 3

Incomplete combustion occurs when there is an insufficient supply of oxygen.
To ensure complete combustion occurs, the reaction should be carried out with excess oxygen.

Question 4

What are the products of incomplete combustion?

Answer 4

Carbon particulates - soot (C)
Carbon dioxide (CO(2))
Carbon monoxide (CO)
Water (H(2)O)

Question 5

Write a balanced symbol equation for the incomplete combustion of methane to form carbon monoxide and water

Answer 5

Question 6

Write a balanced symbol equation for the incomplete combustion of methane to form carbon particulates and water

Answer 6

Question 7

What are the benefits and drawbacks related to the burning of fossil fuels for energy?

Answer 7

Question 8

What type of bonds are the C-C and C-H bonds in alkanes?

Answer 8

σ-bond
(Sigma bond)

Question 9

Give an example of a type of reaction that uses a radical substitution mechanism?

Answer 9

Photochlorination of alkanes

Question 10

What is a photochlorination reaction?

Answer 10

A photochlorination reaction occurs when one of the hydrogen atoms on an alkane is replaced by a chlorine atom. The reaction is initiated by light.

Question 11

Compare the difference in reactivity of alkanes and alkenes

Answer 11

Alkenes have a high electron density in the carbon-carbon double bond, C=C. This makes them more susceptible to attacks from electrophiles, compared to alkanes, making alkenes more reactive.

Question 12

Describe the C=C bond in alkenes in terms of the types of covalent bonds present

Answer 12

Question 13

What is Streoisomerism (in terms of E-Z isomerism)

Answer 13

Stereoisomerism occurs when isomers have the same structural formula but a different arrangements of atoms in space due to the limited rotation around the carbon-carbon double bond.
Isomers are normally referred to as E- or Z- isomers.

Question 14

How do you determine whether an isomer is E- or Z-?

Answer 14

● In E- isomers, high priority groups are on opposite sides of the C=C bond.
● In Z - isomers, high priority groups are on the same side of the C=C bond.

Question 15

Answer 15

Question 16

Why can alkenes undergo electrophilic addition?

Answer 16

Alkenes are susceptible to attack from electrophiles because of the high electron density in the C=C double bond

Question 17

Describe the electrophilic addition of bromine to ethene, including diagrams.

Answer 17

Question 18

Which qualitative tests can be carried out to test for alkenes?

Answer 18

Add bromine water: The orange solution decolourises if the alkene C=C bond is present.
- Add acidified potassium dichromate: The purple solution decolourises if the alkene C=C bond is present.

Question 19

Give the mechanism for the electrophilic addition of hydrogen bromide to propene

Answer 19

Question 20

Explain why the electrophilic addition of bromine to propene can produce a major and a minor product

Answer 20

When propene undergoes electrophilic addition, two possible products can be formed: the major and the minor product. This is because two different carbocation intermediates can be formed - the primary and the secondary carbocation. The secondary carbocation is more stable so this produces the major product 2-bromopropane. The primary carbocation forms the minor product 1-bromopropane.

Question 21

What reaction does an alkene undergo to form an alkane? Name the reagents and conditions

Answer 21

Question 22

What is addition polymerisation?

Answer 22

Addition polymerisation occurs when lots of monomers with carbon-carbon double bonds join together to form a long chain polymer.
The 𝝅 bond breaks and the electrons are used to form 𝛔 bonds with other monomers either side of it.
Atom economy is 100%.

Question 23

What is a repeat unit?

Answer 23