Hydrocarbons Flashcards
What are hydrocarbons?
Hydrocarbons are organic compounds made of hydrogen and carbon atoms.
Hydrocarbons are the simplest organic compounds.
What is the general formula for alkanes?
The general formula for alkanes is CnH2n+2.
Alkanes are saturated hydrocarbons.
List the first four alkanes.
- Methane: CH4
- Ethane: C2H6
- Propane: C3H8
- Butane: C4H10
These are the simplest alkanes.
What defines alkanes?
Alkanes have all C-C single bonds and are saturated compounds.
Each carbon atom in alkanes forms four single covalent bonds.
How do hydrocarbon properties change with carbon chain length?
- Shorter carbon chains are less viscous
- Shorter carbon chains are more volatile
- Shorter carbon chains are more flammable
These properties influence their uses as fuels.
What occurs during complete combustion of hydrocarbons?
Complete combustion produces carbon dioxide and water vapor, releasing energy.
The reaction is: hydrocarbon + oxygen → carbon dioxide + water (+ energy).
What is oxidation in the context of hydrocarbons?
Oxidation is defined as the gain of oxygen.
During combustion, both carbon and hydrogen from hydrocarbons are oxidized.
What is the balanced equation for the complete combustion of methane (CH4)?
CH4 + 2O2 → CO2 + 2H2O.
This equation balances the number of atoms on both sides.
What is the relationship between carbon chain length and viscosity?
As carbon chain length decreases, viscosity decreases (more runny).
Shorter hydrocarbons are less gloopy.
Fill in the blank: The shorter the carbon chain, the more _______ a hydrocarbon is.
flammable.
True or False: Hydrocarbons are used as fuels due to the low energy released during combustion.
False.
Hydrocarbons release a lot of energy when combusted completely.
What is a displayed formula in the context of hydrocarbons?
A displayed formula shows all the atoms and bonds in a molecule.
It visually represents the structure of the hydrocarbon.
How does flammability change with carbon chain length?
Shorter carbon chains are more flammable (easier to ignite).
This affects their practical applications as fuels.
What is crude oil formed from?
The remains of marine organisms, mainly plankton, buried under sediment over millions of years.
Why are fossil fuels considered non-renewable?
They take millions of years to form, and we are using them faster than they can be replenished.
What is fractional distillation?
A process used to separate different hydrocarbon fractions in crude oil based on their boiling points.
Define hydrocarbons.
Molecules containing only hydrogen and carbon.
What happens to crude oil during fractional distillation?
It is heated to convert most of it into gas, which is then separated in a fractionating column.
Describe the temperature gradient in a fractionating column.
It is hot at the bottom and gets cooler as you go up.
What happens to longer hydrocarbons during fractional distillation?
They have high boiling points, condense back into liquids, and drain out early near the bottom of the column.
What is LPG primarily composed of?
Propane and butane.
Where does petrol drain in a fractionating column compared to diesel?
Petrol drains further up the column than diesel, indicating it has a lower boiling point.
List the fractions obtained from crude oil in order of increasing boiling point.
- LPG
- Petrol
- Kerosene
- Diesel oil
- Heavy fuel oil
- Bitumen
True or False: Crude oil is a finite resource.
True.
Fill in the blank: Hydrocarbons are molecules containing only ______ and ______.
hydrogen, carbon
What is the significance of the boiling points of hydrocarbons in fractional distillation?
They determine where in the column the hydrocarbons will condense and drain out.
What does the term ‘fraction’ refer to in the context of fractional distillation?
A mixture of hydrocarbons that contain a similar number of carbon atoms.
What are some important products derived from crude oil?
- Fuel oil
- Liquid petroleum gas (LP)
- Polymers
- Solvents
- Lubricants
- Detergents
These products are examples of organic compounds that come from crude oil.
What are homologous series?
Groups of similar compounds with many properties in common
Examples include alkanes and alkenes.
What is the purpose of cracking in petroleum processing?
To split long-chain hydrocarbons into shorter, more useful ones
Short-chain hydrocarbons are more flammable and in high demand.
What type of hydrocarbons does cracking produce?
- Alkanes
- Alkenes
Alkenes are used as starting materials for making other compounds and polymers.
What is the process of catalytic cracking?
Vaporizing long-chain hydrocarbons and passing them over a hot powdered aluminium oxide catalyst
This process splits the long-chain molecules on the surface of the catalyst.
What is steam cracking?
Vaporizing hydrocarbons, mixing them with steam, and then heating to a very high temperature
This method is another way to crack hydrocarbons.
Fill in the blank: Cracking is a thermal _______ reaction.
decomposition
What must be balanced in chemical equations for cracking?
The number of carbon and hydrogen atoms on both sides of the equation
This ensures the law of conservation of mass is followed.
What are the examples of long-chain hydrocarbons mentioned?
- Decane (ten C atoms)
- Octane (eight C atoms)
These examples illustrate the types of hydrocarbons that can be cracked.
True or False: Short-chain hydrocarbons are less useful than long-chain hydrocarbons.
False
What are some important products derived from crude oil?
- Fuel oil
- Liquid petroleum gas (LP)
- Polymers
- Solvents
- Lubricants
- Detergents
These products are examples of organic compounds that come from crude oil.
What are homologous series?
Groups of similar compounds with many properties in common
Examples include alkanes and alkenes.
What is the purpose of cracking in petroleum processing?
To split long-chain hydrocarbons into shorter, more useful ones
Short-chain hydrocarbons are more flammable and in high demand.
What type of hydrocarbons does cracking produce?
- Alkanes
- Alkenes
Alkenes are used as starting materials for making other compounds and polymers.
What is the process of catalytic cracking?
Vaporizing long-chain hydrocarbons and passing them over a hot powdered aluminium oxide catalyst
This process splits the long-chain molecules on the surface of the catalyst.
What is steam cracking?
Vaporizing hydrocarbons, mixing them with steam, and then heating to a very high temperature
This method is another way to crack hydrocarbons.
Fill in the blank: Cracking is a thermal _______ reaction.
decomposition
What must be balanced in chemical equations for cracking?
The number of carbon and hydrogen atoms on both sides of the equation
This ensures the law of conservation of mass is followed.
What are the examples of long-chain hydrocarbons mentioned?
- Decane (ten C atoms)
- Octane (eight C atoms)
These examples illustrate the types of hydrocarbons that can be cracked.
True or False: Short-chain hydrocarbons are less useful than long-chain hydrocarbons.
False
What are alkenes?
Alkenes are unsaturated hydrocarbons that contain a C=C double bond
They are distinct from alkanes, which do not have double bonds.
What does the C=C double bond in alkenes indicate?
Alkenes have two fewer hydrogens compared to alkanes with the same number of carbon atoms
This unsaturation makes them reactive.
List the first four alkenes.
- Ethene
- Propene
- Butene
- Pentene
Each alkene has a corresponding number of carbon atoms.
What is the general formula for alkenes?
CₙH₂ₙ
This indicates that for every carbon atom, there are twice as many hydrogen atoms.
How do alkenes burn in the presence of oxygen?
Alkenes can combust completely to produce water and carbon dioxide, but often undergo incomplete combustion
Incomplete combustion produces carbon and carbon monoxide.
What is produced during incomplete combustion of alkenes that is not produced during complete combustion?
- Carbon
- Carbon monoxide (CO)
Incomplete combustion occurs due to insufficient oxygen.
What is the color of the flame produced by incomplete combustion of alkenes?
Smoky yellow flame
This is due to the production of carbon particles.
True or False: Alkenes have a C=C bond.
True
This differentiates them from alkanes, which have only single bonds.
Fill in the blank: The alkene with the chemical formula C₈H₁₄ contains _______ carbon atoms.
eight
What happens to the double bond in alkenes during a reaction?
The C=C double bond can open up to form single bonds, allowing bonding with other atoms
This increases their reactivity.
Provide an example of an equation for incomplete combustion of an alkene.
C₈H₁₄ + O₂ → 2C + 2CO + 4H₂O
The specific products may vary based on oxygen availability.
What type of reactions do alkenes primarily undergo?
Addition reactions
Alkenes react most of the time via addition reactions, where the carbon-carbon double bond opens to form a single bond and new atoms are added.
What is hydrogenation?
The addition of hydrogen to an alkene
Hydrogenation involves reacting an alkene with hydrogen in the presence of a catalyst to form a saturated alkane.
What characterizes alkenes as a homologous series?
Same functional group and similar reactions
Alkenes are a homologous series because they all share the same functional group, leading to similar chemical behavior.
What product is formed when alkenes react with steam?
Alcohols
When alkenes react with steam, water is added across the double bond to form alcohols.
How is ethanol industrially produced from ethene?
By mixing ethene with steam and passing it over a catalyst
The reaction mixture is then condensed, allowing for the separation of ethanol and water from unreacted ethene.
What happens to the boiling points of ethanol and water compared to ethene?
Ethanol and water have higher boiling points than ethene
This property allows for the condensation and subsequent purification of ethanol from the reaction mixture.
What type of compounds do alkenes form when they react with halogens?
Saturated compounds
The addition of halogens such as bromine or chlorine to alkenes results in saturated compounds.
What is the reaction of bromine with ethene called?
Dibromoethane formation
The reaction between ethene and bromine produces dibromoethane, as two bromine atoms are added.
What indicates a reaction has occurred when bromine water is added to an alkene?
The bromine water becomes colourless
The decolourisation of orange bromine water indicates that the alkene has reacted, forming a colourless dibromo-compound.
When bromine water is added to a saturated compound, what is the expected observation?
The solution remains bright orange
No reaction occurs with saturated compounds like alkanes, thus the colour remains unchanged.
Fill in the blank: The presence of a _______ catalyst at 60 °C is necessary for hydrogenation.
nickel
Nickel is commonly used as a catalyst in the hydrogenation of alkenes.
