Alkanes Flashcards
What is the general formula for alkanes?
CnH2n +2
What is the polarity of alkanes like?
Alkanes are non-polar due to similar electronegativity between carbon and Hydrogen. They only contain van der Waals
What is the boiling point of alkanes like?
The boiling points of alkanes increase as chain length increases as there becomes more van der Waals.
Why do branched alkanes have a lower boiling point than unbranched?
Branched chains cannot pack closely together so there are fewer points of contact therefore less van der Waals
What is the solubility of alkanes like?
Alkanes are insoluble in water.
Non-polar molecules dissolve in polar solvents but alkanes do dissolve only in non-polar solvents eg.oil
What is the reactivity of alkanes like?
Alkanes are unreactive however they react with halogens with specific conditions
- They have strong C-C and C-H bonds and they burn with oxygen in combustion
What is a finite resource?
Being used faster than it is being formed
What are bubble caps?
They increase contact time between vapour and the liquids in the tower and help to collect liquids that form at various heights
What is cracking?
It is the process of longer chain fractions of alkanes are broken into shorter ones
Which are more reactive alkanes or alkenes?
Alkenes
What are the two types of cracking?
Thermal and Catalytic
What are the conditions and what happens during thermal Cracking?
- Heat alkanes at high temperature (700-1200K)
- High pressure (up to 7000kPa)
- It produces hydrogen gas
- Very short process (1 sec ) to avoid the decomposition of Carbon and Hydrogen
- Avoids the highest number of alkenes
What are the conditions of Catalytic pressure and what happens
- Takes place at high pressure (720PkPa) which is slightly lower than thermal
- Slight pressure ( higher than atmospheric)
- Involves the use of a Zeolite Catalyst ( made of silicon dioxide and aluminium oxide)
-This produces branched alkanes
What are some environmental problems caused by these pollutants?
Carbon Monoxide
Nitrogen Oxide
Sulphur Dioxide
Carbon particulates
Unburnt hydrocarbons
Carbon Dioxide
Water Vapour
- Poisonous
- Acid rain and Photochemical smog
-Acid rain
-Breathing problems
-Photochemical smog - Greenhouse gas
- Greenhouse gas
What is the difference between complete combustion and incomplete combustion?
Complete combustion is where there is plentiful of oxygen whereas there isn’t enough oxygen in incomplete combustion
Describe Carbon Monoxide and what it does?
- It is a toxic gas
- Colourless and Odourless
- Binds to haemoglobin
- Side effects are nausea, loss of consciousness and dizzines
Describe Nitrogen Oxide and what it does?
Nitrogen and oxygen from the atmosphere forms nitrogen monoxide at a very high temperature in a petrol engine when the sparks ignite the fuel. N2 (g) + O2 (g) —> 2NO (g)
- Nitrogen monoxide is converted into Nitrogen Dioxide in the air
2NO (g) + O2 (g) —> 2NO2 (g)
Describe what Sulphur Dioxide is and what it does?
It is produced by the combustion of Sulphur containing fossil fuels
- It isn’t usually in car engines as it is removed from petrol.
- When burnt it forms Sulphur Dioxide which can cause breathing difficulties and asthma attacks.
- Sulphur dioxide causes acid rain, when it reacts with water vapour and oxygen in the air to form Sulphuric acid
: S02 + H20 + 1/2O2 —> H2SO4
- Flues or chimneys contain Cao or CaCO3 to absorb sulphur dioxide , they are bases so they neutralise acidic sulphur dioxide ( flue gas desulfurisation)
-CaO+2H20 +SO2 +O.5O2 —> CaSO4 + 2H20
-CaCO3 + 0.5O2 + SO2 —> CaSO4 + CO2
What are cataytic converters?
They use a platinum and rhodium metal catalyst to form non- toxic gases such as CO2 + H20 and N2
Write the equations for nitrogen dioxide , carbon monoxide and nitrogen oxide going through a catalyst converter.
NO2 (g) —> N2 (g) + 2O2 (g)
CO (g) + 0.5O2 (g) —> CO2 (g)
2NO (g) + 2CO (g) —-> N2 (g) + 2CO2 (g)
