2.5 Hydrocarbons Flashcards
What are the only products when a
hydrocarbon fuel undergoes complete
combustion?
Water (H2O) and carbon dioxide (CO2)
Write a balanced chemical equation for the complete combustion of ethane
2C2H6 + 7O2 → 4CO2 + 6H2O
Write a balanced chemical equation for the complete combustion of ethane
2C2H6 + 7O2 → 4CO2 + 6H2O
When does incomplete combustion occur? What is required to ensure complete combustion occurs?
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.
What are the products of incomplete
combustion?
Carbon particulates - soot (C)
Carbon dioxide (CO2)
Carbon monoxide (CO)
Water (H2O)
Write a balanced symbol equation for the
incomplete combustion of methane to
form carbon monoxide and water
2CH4 + 3O2→ 2CO + 4H2O
Write a balanced symbol equation for the
incomplete combustion of methane to
form carbon monoxide and water
2CH4 + 3O2→ 2CO + 4H2O
advantages of fossil fuels
produces large amounts of energy
currently relatively easily available
disadvantages of fossil fuels
uses infinite resources
releases CO2 which contributes to global warming
releases carbon monoxide which is toxic
produces acidic gases which causes acid rain
incomplete combustion eg propane
propane + oxygen—>carbon dioxide + carbon monoxide
What type of bonds are the C-C and C-H
bonds in alkanes?
σ-bond
(Sigma bond)
Give an example of a type of reaction
that uses a radical substitution
mechanism?
photochlorination of alkanes
What is a photochlorination reaction?
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.
Compare the difference in reactivity of
alkanes and alkenes
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.
Describe the C=C bond in alkenes in
terms of the types of covalent bonds
present
The C=C has a normal σ-bond as well as a π-bond located above and below the σ-bond.
σ-bond: sigma bond
π-bond: pi bond
What is stereoisomerism (in terms of E-Z
isomerism)?
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.
How do you determine whether an isomer is E- or Z-?
● 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.
Why can alkenes undergo electrophilic
addition?
Alkenes are susceptible to attack from
electrophiles because of the high
electron density in the C=C double bond
Which qualitative tests can be carried out
to test for alkenes?
- Add bromine water: The orange solution decolourises if the alkene C=C bond is present.
- Add acidified potassium dichromate: The purple solution decolorises if the alkene C=C bond is present.
Explain why the electrophilic addition of
bromine to propene can produce a major
and a minor product
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- bromopropene. The primary carbocation forms the minor product 1-bromopropane.
What reaction does an alkene undergo to form an alkane? Name the reagents and conditions
● Reaction type: Hydrogenation
● Reagents: Hydrogen gas, H2
● Conditions: Nickel catalyst, 150℃
What is addition polymerisation?
Addition polymerization 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 on either side of it.
Atom economy is 100%.
what is a repeat unit?
A single unit of a polymer derived from its monomer, the repetition of which
would result in the polymer.
