Ngā Whāinga Ako ^🔗

• Recognise that a hydrocarbon contains only C and H atoms
• Name and write the formula for the first six hydrocarbons

Hydrocarbon Formation ^🔗

1. Layers of dead organic matter settle on the seabed.
2. Layers of sedimentary rock build up on top.
3. The heat and pressure from these rocks, along with the absence of oxygen mean that oil and gas (fossil fuels) are formed over millions of years.

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Crude Oil ^🔗

Crude oil is what we get directly out of the ground and is made of a mixture of lots of different hydrocarbons (molecules made of only hydrogen and carbon).

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Hydrocarbons ^🔗

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• A hydrocarbon with 4 carbons is called butane
• A hydrocarbon with 5 carbons is called pentane
• A hydrocarbon with 6 carbons is called hexane
• Can you guess what 7, 8, 9 and 10 are called?

Hydrocarbon Formula ^🔗

• Methane has 1 carbon and 4 hydrogens so it is called $CH_{4}$
• Ethane has 2 carbons and 6 hydrogens so it is called $C_{2}H_{6}$
• Propane has 3 carbons and 8 hydrogens so it is called $C_{3}H_{8}$
• What is the pattern? Try write a general formula using n to represent the number of carbons..

Answer ^🔗

\begin{aligned} C_{n}H_{2n+2} \end{aligned}

Calculating Hydrocarbons ^🔗

\begin{aligned} C_{n}H_{2n+2} \end{aligned}

Using this formula you can calculate the formula for any hydrocarbon!

1. Find the formula for the 17th hydrocarbon
2. Find the formula for the 56th hydrocarbon
3. Find the formula for the 117th hydrocarbon

Answers ^🔗

1. $C_{17}H_{36}$
2. $C_{56}H_{114}$
3. $C_{117}H_{236}$

Hydrocarbon Properties ^🔗

A longer chain of carbons means:

• Less ability to flow (higher viscosity)
• Less flammable
• Less volatile
• Higher boiling point

Making Alkanes ^🔗

IN PAIRS OR GROUPS, WRITE FORMULA AND MAKE MODELS FOR THESE ALKANES:

1. An alkane with one carbon molecule
2. An alkane with three carbon molecules
3. An alkane with six carbon molecules

You may need to join groups to make the larger molecules.

Hands up for check each time!

Combustion of Hydrocarbons ^🔗

Try and conmplete these word and symbol equations (refer to your notes):

Complete Combustion

\begin{aligned} methane + oxygen \rightarrow \hspace{1cm} + \hspace{1cm}\newline CH_{4} + \frac{1}{2}O_{2} \rightarrow \hspace{2cm} + \hspace{2cm} \end{aligned}

Incomplete Combustion

\begin{aligned} CH_{4} + \frac{1}{2}O_{2} \rightarrow \hspace{2cm} + \hspace{2cm} \end{aligned}