chemistry Flashcards
what is a hydrocarbon?
A hydrocarbon is any compound which only contains carbon and hydrogen atoms. E.g. C10H22
What is an alkane?
An alkane is a saturated hydrocarbon (saturated means no double bonds).
What is the main product of complete combustion of hydrocarbons?
Carbon dioxide and water
what is the general formula for alkanes?
CnH2n+2
what are 3 properties of short hydrocarbons?
Volatile - low boiling point.
Runny - low viscosity (not thick & gloopy).
Flammable.
What does the term ‘saturated’ mean when talking about hydrocarbons?
Saturated means that there are no carbon-carbon double bonds.
Are alkanes saturated or unsaturated?
saturated
Which type of hydrocarbon has only single bonds?
Alkanes
What is crude oil primarily composed of?
Crude oil is primarily composed of hydrocarbons.
True or False: Crude oil is formed from the remains of ancient marine organisms.
True.
Fill in the blank: Crude oil is formed over millions of years under high _____ and _____ conditions.
temperature; pressure.
Fill in the blank: The process of breaking down larger hydrocarbons into smaller ones is known as _____
cracking.
What is crude oil?
A finite resource found in rocks, originating from ancient biomass buried millions of years ago.
Mainly consists of plankton and other organic materials.
List the first four alkanes and their formulas.
- Methane → CH₄
- Ethane → C₂H₆
- Propane → C₃H₈
- Butane → C₄H₁₀
What is fractional distillation?
A process used to separate crude oil into fractions based on the number of carbon atoms in hydrocarbons. and their boiling points
Each fraction contains hydrocarbons with similar molecular sizes.
Describe the key processes in fractional distillation.
- Evaporation: Crude oil is heated, turning hydrocarbons to gas.
- Condensation: Gases cool and condense at different levels in the fractionating column.
Where do smaller molecules condense in fractional distillation?
At the top of the fractionating column (lower boiling points).
Larger molecules condense lower down.
How do the properties of hydrocarbons change with molecular size?
- Boiling point increases
- Viscosity increases
- Flammability decreases
What happens during the combustion of hydrocarbons?
Releases energy, producing carbon dioxide (CO₂) and water (H₂O).
Example equation: CH₄ + 2O₂ → CO₂ + 2H₂O.
What is cracking in relation to hydrocarbons?
A process that breaks down long-chain hydrocarbons into shorter, more useful molecules, producing alkanes and alkenes.
What are the two methods of cracking?
- Catalytic cracking → Uses a hot catalyst
- Steam cracking → Uses high temperature and steam
How do alkenes differ from alkanes?
Alkenes are more reactive than alkanes.
They can undergo additional reactions due to the presence of a double bond.
What is the test for alkenes?
Add bromine water: If an alkene is present, the orange bromine water turns colourless.
Do alkanes change the colour of bromine water?
No, alkanes do NOT change the colour of bromine water.
Why is cracking useful?
High demand for small hydrocarbons and alkenes are valuable for making polymers and other chemicals.
what is the equation for complete combustion?
Alkane + oxygen —-> carbon dioxide + water
are long chain or short chain hydrocarbons highly flammable?
short chain
are short chain or long chain hydrocarbons viscous?
long Chaim
do short chain or long chain hydrocarbons have high boiling points?
long chain
what chemicals are alchenes used to make?
polymers
what is the test for achenes?
bromine water from orange to colourless
