Unit 2 - Hydrocarbons Flashcards
What is a fuel?
Fuels are substances which are burnt to produce energy.
The energy is stored as chemical energy and is released as heat and light energy when burnt.
What is crude oil?
Crude oil is a very complex mixture of chemical compounds called hydrocarbons.
What elements are in hydrocarbons?
Hydrocarbons contain carbon and hydrogen only.
What is combustion?
Combustion is the burning of a substance in oxygen.
What type of reaction is combustion?
Exothermic reaction because heat energy is released.
What components need to be present for a fire to continue?
Fuel
Oxygen
Heat
How is crude oil (hydrocarbons) separated?
How are the fractions separated?
The crude oil needs to be separated using a process called fractional distillation.
The fractions are separated by the difference in their temperature ranges.
What is always produced during the combustion of any hydrocarbon?
Carbon dioxide, water
Properties of fractions - hydrocarbons chains
Hydrocarbons are made up of chains of carbon atoms of different lengths.
(Some with only one or two carbon atoms; others with seventy carbon atoms.) The length of the hydrocarbon chain affects the physical and chemical properties of the fractions.?
What is viscosity?
Viscosity is the thickness of a liquid.
What happens is a substance is more Volatile or less Volatile?
The more volatile a substance is, the more easily it evaporates.
The less Volatile a substance is, the less easily it evaporates.
What is incomplete combustion?
If there is INSUFFICIENT oxygen to completely burn a fuel, incomplete combustion occurs.
What is a catalytic convertor?
A catalytic convertor is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into a less toxic pollutant.
What type of energy is released when a fuel burns?
When a fuel burns it releases energy, this is known as an exothermic reaction. (Releases heat energy)
Formula for measuring energy by heating up water?
Specific Heat Capacity of water
Eh = cm🔺️T
Eh=
c =
m =
🔺️T =
What are alkanes?
Alkanes are a group of hydrocarbons that are made up of chains of carbon atoms joined together by single covalent bonds.
What are alkanes described as?
Saturated because each carbon atom has the max number of hydrogen atoms that can bond to it (the carbon).
General formula of alkanes
C(n)H(2n+2)
Properties of alkanes
Saturated hydrocarbons - Alkanes have all there bonds used, so they are unreactive.
Insoluble in water
Used as fuels
How are alkenes produced?
AlkENES are produced from cracking of long chain alkanes.
What is cracking?
Cracking is breaking up long chain alkanes into more useful short chain products.
A mixture of alkanes and alkenes are produced.
General formula of alkenes
CnH2n
Properties of alkenes
Alkenes are unsaturated hydrocarbons.
They are chemically reactive (used to make polymers and alcohols via addition reactions)
Insoluble in water
What are cycloalkanes?
Cycloalkanes are SATURATED hydrocarbons.
What are cycloalkenes?
Cycloalkenes are UNSATURATED hydrocarbons.
Definition of a homologous series?
A family of hydrocarbons with the same general formula and similar chemical properties.
The physical properties change as the carbon chain increases.
Definition of an isomer
Isomers are compounds with the same molecular formula but different structural formula.
What are functional groups?
Identifying features are called functional groups.
AlkENES and cycloalkANES
Alkenes and cycloalkanes are isomers of each other.
Cycloalkanes general formula
CnH2n
This is the same general formula as alkENES.
Cycloalkenes general formula
CnH2n-2
What are addidion reactions?
Addition reactions - adding a small molecule across the carbon-to-carbon double bond.
An addition reaction is when 2 (or more) molecules join together to form a larger one. The reaction involves breaking double C=C double or triple bonds.
Careful for diatomic molecules: e.g. hydrogen = H2
Addition reaction - hydrogenation
Adding H2 to an alkene making and alkane.
What do unsaturated compounds contain?
Unsaturated compounds contain at least one carbon-to-carbon double bonds.
How can unsaturated compounds and saturated compounds be distinguished?
Reacting them with bromine water.
Test for unsaturated definition
Unsaturated compounds turn bromine solution/water colourless.
Physical properties of hydrocarbons
Melting and boiling points increase as the carbon chain increases. This is due to larger intermolecular forces. (NO COVALENT BONDS ARE BROKEN when covalent molecules melt/boil.)
Insoluble in water
DO NOT conduct electricity
Uses of hydrocarbons
Alkanes - fuels
Alkenes - make alcohols and polymers from addition reactions.
Cycloalkanes - solvents, fuels
Carbohydrates
(Carbon, hydrogen, oxygen)
- sugars
- alcohols
- carboxylic acids
Functional group of alcohols
Hydroxyl group (OH)
General formula of alcohols
CnH2n+1OH
Test for starch
The test for starch is the iodine solution turned from red-brown to blue-black.
Test for glucose
The test for glucose is the benedicts’ solution turned from bright blue to brick orange.
Properties of alcohols
Clear liquids
Melting and boiling points increase as chain length increases because larger intermolecular forces.
Viscosity increases
Flammability decreases
1st 3 - soluble in water - after that solubility decreases with chain length.
Uses of alcohols
Fuels
Kills bacteria/ viruses - hand sanitiser, mouthwash
Solvents - substances that may not be soluble in water may be soluble in alcohols.
Energy from fuels test
Draw
Explain stages?
Combustion of alcohol and energy calculations formula
Eh = cm🔺️T
Eh = heat energy (kJ) c = specific heat capacity of water (4.18kJkg-¹°C-¹) m = mass of water (kg) 🔺️T = change in temperature (°C)
Burning fuels experiment inaccuracies and solutions
Heat lost to surroundings
- can be reduced by insulation/ draught excluder
- can reduce distance from burner to metal cup
Incomplete combustion
Fuel evaporates
Burning fuels experiment - Bomb Calorimeter
More accurate because:
- no heat lost due to surroundings (all heat goes to water)
- no incomplete combustion (as there is a constant supply of oxygen)
- no evaporation of fuel (enclosed “bomb”)
What are carboxylic acids?
Carboxylic acids are a homologous series with a carboxyl functional group.
Carboxylic acids general formula
CnH(2n+1)COOH
Properties of Carboxylic acids
- Liquids at room temperature
- melting and boiling points increase with chain/molecule size because the INTERMOLECULAR FORCES INCREASE.
- strong (pungent) smelling
- solubility- 1st 4 acids are soluble in water (solubility decreases as molecule size increases)
Uses of Carboxylic acid
- flavouring
- food preservation
- cleaning products
- medicines
Reactions of Carboxylic acids
React with metals - gives off H2
Neutralise bases - hydroxides, carbonates, oxides
Conduct electricity
What are organic compounds?
Organic compounds are molecules that contain carbon.
First 8 prefix names
1 - meth 2 - eth 3 - prop 4 - but 5 - pent 6 - hex 7 - hept 8 - oct
What is an exothermic reaction
An exothermic reaction is a reaction which releases heat energy.
What is an endothermic reaction?
An endothermic reaction is a reaction which takes in heat energy.
What are identifying features?
Functional groups
What do all alkenes have?
A carbon to carbon double bond. (Or more)
Describe saturated compounds
Saturated compounds only contain C-C single bonds.
Describe unsaturated compounds
Unsaturated compounds contain at least one C=C double bond.
Addition reaction - hydration
Adding H2O to an alkene making an alcohol.
Reaction between an alkene and water forming an alcohol.
Alcohols up to C8
Methanol Ethanol Propan-1-ol Butan-1-ol Pentan-1-ol Hexan-1-ol Heptan-1-ol Octan-1-ol
Carboxylic functional group
Carboxyl (COOH)
Carboxylic acids up to C8
Mathanoic acid Ethanoic acid Propanoic acid Butanoic acid Pentanoic acid Hexanoic acid Heptanoic acid Octanoic acid
Definition of a combustion reaction
Combustion reaction is when a substance reacts with oxygen and releases energy.
When hydrocarbons and alcohols react with oxygen, water and carbon dioxide is released.
What do saturated compounds contain
Only contain C-C single bonds.
