Alkanes Flashcards
What are alkanes?
- Alkanes are saturated hydrocarbons.
General formula for alkanes
CₓH₂ₓ₊₂
General formula for cycloalkanes. Are they saturated hydrocarbons?
-CₓH₂ₓ
Yes, they are saturated hydrocarbons (as there are no C=C double bonds.)
() - extra info for clarification.
What is another word for crude oil?
- Petroleum.
What is crude oil/ petroleum?
- Mixture of different length hydrocarbons- mainly alkane hydrocarbons.
How can hydrocarbons in petroleum/ crude oil be separated? What are the stages of this separation?
- By fractional distillation.
1.) Crude oil vapourised
2.) Vapourised oil enters column and rises.
3.) Column has temperature gradient. As vapour rises, parts of mixture condense at different temperatures.
4.) This is because there are different chain lengths - hence, different boiling points.
5.) The fractions are drawn off at different levels.
What happens to the longest and shortest hydrocarbons during fractional distillation?
- Longest hydrocarbons: don’t vapourise and run down to bottom of column.
- Shortest hydrocarbons: won’t even condense at top of column; so come off as a gas at top of column.
What is cracking?
- Cracking is breaking a longer chain alkane into shorter hydrocarbons.
- It involves breaking the C-C bond in alkanes.
Why is cracking useful?
- Because shorter hydrocarbons are in higher demand than longer hydrocarbons - as they are used as fuel.
What are the two different types of cracking?
- Thermal cracking
- Catalytic cracking.
What are conditions for thermal cracking? What does thermal cracking produce predominantly? Why is the product useful ?
- High temperature and high pressure required: 1000⁰C/ 70 atm
- Thermal cracking produces a high percentage of alkenes - useful as alkenes can be used to make polymers (ie. plastics.)
What are the conditions for catalytic cracking?
- High temperature of 450⁰C
- Slight pressure
- Zeolite catalyst
What is the role of the zeolite catalyst in catalytic cracking?
- Helps lower the temperature and pressure needed for cracking to occur.
- This lowers the cost and speeds up the process.
What are the main products of catalytic cracking?
- Aromatic hydrocarbons (useful in fuels in vehicles) and motor fuels.
What are alkanes predominantly used as, and why?
- Alkanes are used as fuels because most burn readily to produce large amounts of energy.
What are the products for the complete combustion of alkanes?
Carbon dioxide + water
True or False
Only the combustion of ALKANES (specifically) can be either complete or incomplete.
- False.
- Combustion of alkanes AND other organic compounds can be complete or incomplete.
What is complete vs incomplete combustion?
- Complete: fuel burns in plentiful supply of oxygen.
- Incomplete: fuels burns in limited supply of oxygen.
What are the products for incomplete combustion of alkanes?
- Carbon monoxide - CO(g)
- Carbon soot - C(s)
- Unburned hydrocarbons
- Only one of these are formed in one equation, not all in same equation!
What is the issue with carbon monoxide (CO)? How can CO be removed from exhaust fumes in the engine?
- CO is poisonous as it binds to haemoglobin in the blood, preventing oxygen binding.
- CO can be removed using a catalytic converter.
3 problems associated with carbon soot.
1.) Causes breathing problems.
2.) Makes buildings dirty
3.) Clogs up engines.
How is increase in carbon dioxide affecting the environment and HOW?
- Causing global warming.
- Carbon dioxide = greenhouse gas: absorbs infrared radiation from sun/ emitts some of it back into Earth, this is called greenhouse effect.
- All greenhouse gases CONTAIN polar bonds.
How are oxides of nitrogen (NOx) formed/ made?
- Oxygen and nitrogen (naturally in the air) combine/ react due to high pressures and temperatures in car engines.
Give 4 poulltants produced from the internal combustion engines.
1.) NOx (oxides of nitrogen.)
2.) CO
3.) Carbon (soot)
4.) Unburned hydrocarbonds.