Topic 8 Flashcards
(29 cards)
What are hydrocarbons?
Compounds that contain hydrogen and carbon only
What is crude oil? (3)
- a mixture of hydrocarbons containing molecules in which carbon atoms are in chains or rings
- an important source of useful substances (e.g. fuels and feedstock for the petrochemical industry)
- a non renewable (finite) resource
Describe the separation of crude oil by fractional distillation (dont state the uses of the different fractions yet)
- Oil is heated until most of it turns into gas. The gases enter a fractionating column with a temperature gradient (hot at bottom and cooler at the top)
- The longer hydrocarbons have higher boiling points. They turn back into liquids and drain out of the column early on, at the bottom.
- The shorter hydrocarbons have lower boiling points so they turn to liquids and drain out much later on, near the top of the column, where its cooler
Describe the names and uses of the different fractions? (starting from the ones that drain out at the top of the column)
- gases: domestic heating and cooking
- Petrol: Fuel in cars
- Kerosene: Fuel in aircraft
- Diesel oil: fuel in some cars and larger vehicles
- Fuel oil: fuel for large ships and in some power stations
- Bitumen (liquid): to surface roads and roofs
What happens to the number of carbon and hydrogen atoms as you move down the fractionating column?
They increase
Why do bigger molecules have higher boiling points than smaller molecules?
- The intermolecular forces of attraction break a lot more easily in small molecules than they do in bigger molecules because the forces are much stronger between big molecules
- so more energy is needed to overcome the forces in larger molecules
Why are shorter hydrocarbons easy to ignite?
- They have lower boiling points so tend to be gases at room temperature
- These gases mix with oxygen in the air to produce a gas mixture which bursts into flames if it comes into contact with a spark
Why are longer hydrocarbons hard to ignite?
- They are usually liquids at room temp as they have higher boiling points, so they are harder to ignite (they cant ignite like shorter hydrocarbons)
What does viscosity measure?
Viscosity measures how easily a substance flows
what is the viscosity like for shorter/longer hydrocarbon and why?
longer hydrocarbons - high viscosity as the stronger the force is between hydrocarbon molecules, the harder it is for the liquid to flow
Shorter hydrocarbons - Low viscosity as the force is weaker between the molecules
Hydrocarbons are mostly members of the …….. homologous series
alkane
A homologous series is a family of molecules that ….
- have the same general formula
- differ by CH2 in molecular formulae from neighbouring compounds
- show a gradual variaion in physical properties e.g. boiling points
- share similar chemical properties
Describe the complete combustion of hydrocarbon fuels
- They’re exothermic reactions
- Hydrocarbons react with oxygen
- Carbon dioxide and water are given out
What is incomplete combustion?
When a substance e.g. hydrocarbon reacts with a limited supply of oxygen and the products contain less oxygen than carbon dioxide
What does incomplete combustion usually produce?
Carbon monoxide and carbon
Why is carbon monoxide dangerous?
- It can combine with red blood cells and stop your blood from doing its proper job of carrying oxygen around the body
- a lack of oxygen in the blood dupply to the brain can lead to fainting, a coma or even death
What effect can carbon, which is released from incomplete combustion, have on the atmosphere?
- carbon particles can be released into the atmosphere. When they fall back onto the ground, they deposit themselves as soot
- soot can make buildings look dirty, reduce air quality and worsen respiratory problems
How do impuritites in hydrocarbon fuels result in the production of sulfur dioxide, and hence, acid rain?
- When fossil fuels are burned, they can release sulfur dioxide from sulfur impurities in the fossil fuels
- If sulfur dioxide mixes with clouds, it forms dilute sulfuric acid, which then falls as acid rain
Why is acid rain bad?
- It can cause lakes to become acidic and many plants and animals can die as a result
- it can kill trees, damage limestone buildings/stone statues and it can make metal corrode
What does oxygen and nitrogen react together to produce?
Oxides of nitrogen, which are pollutants
What are the advantages of using hydrogen, rather than petrol as a fuel for cars?
- hydrogen is clean as, in a hydrogen fuel cell, the only waste product is water
- its a renewable source
- it can be obtained from the water produced by the cell when its used in fuel cells
What are the disadvantages of using hydrogen, rather than petrol as a fuel for cars?
1- You need a special expensive engine
2- it is hard to store and not widely available
3- to manufacture it, it uses energy from burning fossil fuels
Petrol, Kerosene and diesel oil are (non renewable?/renewable?) and are obtained from ……
- non-renewable
2. crude oil
Methane is a (renewable/non-renewable?) fossil fuel that is found in ……
1- non-renewable
2- natural gas
