Hydrocarbons: Fuel & Feedstock Flashcards

All 29 cards in this deck

What is crude oil?

A finite resource found in rocks, formed from the remains of an ancient biomass (mainly plankton) buried in mud.

What is a hydrocarbon?

A molecule made up of hydrogen and carbon atoms only.

True or false? Crude oil is a single compound.

False. Crude oil is a mixture of a very large number of compounds, most of which are hydrocarbons.

What is the general formula for the homologous series of alkanes?

$\mathrm{C_nH_{2n+2}}$

Name the first four alkanes in order and give their molecular formulae.

Methane $\mathrm{CH_4}$, ethane $\mathrm{C_2H_6}$, propane $\mathrm{C_3H_8}$, butane $\mathrm{C_4H_{10}}$.

How do you check whether a hydrocarbon is an alkane from its molecular formula?

e.g. is $\mathrm{C_6H_{14}}$ an alkane?

1. Count the carbons: $n = 6$
2. Work out $2n+2$: $2\times6+2 = 14$
3. Compare with the hydrogens given: 14 = 14, so yes, it is an alkane.

What name is given to the process used to separate crude oil into fractions?

Fractional distillation.

What do all the hydrocarbon molecules in one fraction of crude oil have in common?

They have a similar number of carbon atoms.

What are the steps in the fractional distillation of crude oil?

e.g. collecting the kerosene fraction

1. Heat the crude oil so the hydrocarbons evaporate (vaporise).
2. Vapours rise up a column with a temperature gradient (cooler going up).
3. Each fraction condenses at the level matching its boiling point — kerosene condenses and is collected at that level.

In a fractionating column, where do hydrocarbons with higher boiling points condense?

Lower down, where the column is hotter.

Name four fuels produced from crude oil.

Petrol, diesel oil, kerosene, heavy fuel oil (also liquefied petroleum gases).

Name four useful materials made by the petrochemical industry from crude oil feedstock.

Solvents, lubricants, polymers and detergents.

True or false? Fractions from crude oil are only used as fuels.

False. They are also processed to give feedstock for the petrochemical industry, making solvents, lubricants, polymers and detergents.

How does the boiling point of a hydrocarbon change as its molecules get larger?

The boiling point increases.

How do viscosity and flammability change as hydrocarbon molecules get larger?

Viscosity increases (flows less easily) and flammability decreases.

True or false? Hydrocarbons with larger molecules ignite more easily.

False. Flammability decreases as molecular size increases, so larger molecules are harder to ignite.

What two products are formed by the complete combustion of a hydrocarbon?

Carbon dioxide and water.

What happens to the carbon and hydrogen in a fuel during combustion?

They are oxidised, and energy is released.

What are the steps to balance an equation for the complete combustion of a hydrocarbon?

e.g. $\mathrm{CH_4 + O_2 \rightarrow}$

1. Products are $\mathrm{CO_2}$ and $\mathrm{H_2O}$: $\mathrm{CH_4 + O_2 \rightarrow CO_2 + H_2O}$
2. Balance C then H: $\mathrm{1\,CO_2}$ and $\mathrm{2\,H_2O}$
3. Balance O last using $\mathrm{O_2}$: $\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$

Why is a fraction such as petrol useful as a fuel for a car engine?

Its molecules are small, so it has a low boiling point, low viscosity and is highly flammable.

What is cracking?

Breaking down large hydrocarbon molecules into smaller, more useful molecules.

What are the conditions used for catalytic cracking?

Heat the hydrocarbon to vaporise it and pass the vapour over a hot catalyst.

What are the conditions used for steam cracking?

Vaporise the hydrocarbon, mix it with steam and heat to a very high temperature.

Which two types of hydrocarbon are produced by cracking?

Alkanes and alkenes.

Why is cracking carried out in industry?

Demand for small hydrocarbons (fuels) is greater than the supply, and cracking also makes alkenes for polymers and other chemicals.

What is the test for an alkene, and the colour change seen?

Add bromine water: it changes from orange to colourless.

True or false? Alkanes decolourise bromine water.

False. Alkenes are more reactive and decolourise bromine water; alkanes leave it orange.

How do you balance an equation for a cracking reaction?

e.g. $\mathrm{C_{10}H_{22} \rightarrow C_8H_{18} + \;?}$

1. Count carbons on each side: $10 - 8 = 2$ left over.
2. Count hydrogens: $22 - 18 = 4$ left over.
3. Missing product is $\mathrm{C_2H_4}$: $\mathrm{C_{10}H_{22} \rightarrow C_8H_{18} + C_2H_4}$

True or false? Alkenes are more reactive than alkanes.

True. Their greater reactivity is why alkenes react with bromine water but alkanes do not.