chemistry topic 5 hydrocarbons

what are covalent bonds

non metal - non metal

what are the weak intermolecular forces of attraction also known as

Van der Waals forces

what do Van der Waals forces depend on?

the number of electrons per molecule, and the distance between the molecules. the more electrons per molecule and the closer together the molecules, the stronger the intermolecular forces

how do intermolecular forces affect boiling points

the stronger the intermolecular forces, the higher the boiling points

how do intermolecular forces affect viscosity

the stronger the intermolecular forces, the higher the viscosity

how do intermolecular forces affect flammability

the stronger the intermolecular forces, the lower the flammability

what happens to alkanes' melting and boiling point as you go down

increases

how is crude oil formed

crude oil is a fossil fuel formed over 300 mya, when plankton and other sea creatures died, fell to the sea bed and became covered by sediment. as no oxygen got to the dead bodies, heat and pressure built up and turned them to hydrocarbons

how is crude oil refined using fractional distillation

crude oil is extracted from the ground, is vapourised, and enters the fractionating column as a gas. the column is hot at the bottom and cooler at the top. the different fractions condense at different heights, as fractions with lower boiling points condense at the top, and higher boiling points condense farther down. short-chain alkanes have low boiling points so they condense at the top, whereas long chain alkanes have high boiling points so they condense at the bottom

What is the general formula for alkanes?

CnH2n+2

What are the first four alkanes of the homologous series

methane CH4, ethane C2H6, propane C3H8, butane C4H10

what is the difference between complete and incomplete combustion

complete has carbon dioxide and water as products, incomplete has limited oxygen and produces carbon monoxide

what is the rule for balancing equations with C, H and O

balance C and H from left-right, O from right-left

what are the pollutants produced by combustion of hydrocarbon fuels

complete combustion makes carbon dioxide - greenhouse gas - global warming. incomplete combustion makes carbon monoxide and carbon particles - global warming. some contain sulphur - burns to form sulphur dioxide - when dissolved forms acid rain

what are the environmental impacts of burning fuel in a car engine?

nitrogen oxides - contributes to acid rain and can irritate the lungs, causing asthma in children. carbon dioxide - greenhouse gas which contributes to global warming

how are alkanes cracked to make alkenes

cracking is where alkanes are broken down into smaller alkenes, where alkanes are heated to high temperatures with steam or with a catalyst. during cracking, strong double carbon bonds are broken, which requires a lot of energy. oxygen also needs to be excluded.

why is cracking necessary

cracking is useful because there is more demand for the smaller alkanes and alkenes than for substances which have high boiling points

What is the general formula for alkenes?

CnH2n

What are the first four alkenes of the homologous series

ethene C2H4, propene C3H6, butene C4H8, pentene C5H10

what does saturated mean

contains only single bonds between carbon atoms and holds the maximum number of hydrogen atoms

what does unsaturated mean

contains double/triple bonds between carbon atoms, meaning it has fewer hydrogen atoms

how can unsaturated substances be tested using bromine water?

alkenes react with bromine water, turning it from orange to colourless. they can also react with iodine solution, turning it from brown to colourless. the bromine or iodine atoms add to the double bond

how are polymers formed from monomers

the alkene monomers link together to form a long chain of repeating units called a polymer

what does the n in the formula indicate in polymers

the n in the formula indicates the number of repeating units, which has the same number and type of atoms as the monomer because no other molecule is formed in the reaction

what are the differences in properties and structure between LDPE and HDPE

LDPE has branched chains, which stop the polymer molecules from lining up regularly. Its structure is not crystalline, which means that it has a lower density than HDPE because the intermolecular forces between polymer molecules are weaker. HDPE does not have side branches, and the polymer molecules line up regularly to give a crystalline structure

relate the uses of polymers to their properties

LDPE is soft, has a low density and is flexible, and has a low melting point, so it can be used for plastic bags, plastic films, and squeeze bottles. HDPE has a high density, is more resistant and hard, and has a high melting point, so it can be used for bottles, fuel tanks, and water and gas pipes

how are polymers biodegradable and what has been done for safe disposal

addition polymers do not biodegrade easily when buried in soil. They can be incinerated but this makes carbon dioxide a greenhouse gas and also makes toxic fumes.

what is the difference between thermosetting and thermo-softening polymers

Most addition polymers are thermo-softening polymers, which means that they become soft when heated and can be shaped easily. They do not have a single, sharp melting point as they are mixtures of

molecules of different lengths. Thermosetting polymers form cross links between chains and cannot be reshaped by heating