Fuels and Earth Science

what are hydrocarbons?

compounds that contain hydrogen and carbon atoms only

unsaturated hydrocarbon

hydrocarbon containing one or more double bond

alkeness

saturated hydrocarbon

only single bonds between carbon atoms

alkanes

alkane general formula

CₙH₂ₙ₊₂

alkene general formula

CₙH₂ₙ

describe crude oil

- a complex mixture of hydrocarbons

- containing molecules in which carbon atoms are in chains or rings

- an important source of useful substances (fuels etc)

- a finite resource

what hydrocarbons have higher boiling points?

longer chained hydrocarbons

fractional distillation of crude oil

1) the different hydrocarbons have different boiling points

2) the crude oil gets continuously piped in at the bottom

3) it is heated in the fractionating column

4) the hydrocarbons evaporate and rise up the column and the various fractions are tapped off at the different levels where they condense

5) the fractions can be process to produce fuels

what are the more useful products from crude oil?

shorter chain hydrocarbons

use for gases

domestic heating and cooking

use for petrol

fuel for cars

use for kerosene

fuel for aircraft

use for diesel oil

fuel for some cars and trains

use for fuel oil

fuel for large ships and in some power stations

use for bitumen

surface roads and roofs

as you go up the fractions, the number of carbon and hydrogen atoms in their molecules...

...decrease

as you go up the fractions, the boiling points...

...decrease

as you go up the fractions, the ease of ignition...

...increases

as you go up the fractions, the viscosity...

...decreases

what are the 4 characteristics of a homologous series?

A series of compounds which...

1) have the same general formula

2) differ by CH2 in molecular formulae from neighouring compounds

3) show a gradual variation in physical properties, as exemplified by their boiling points

4) have similar chemical properties

what is produced in the complete combustion of hydrocarbons?

- carbon dioxide and water are produced

- energy is given out

why does the incomplete combustion of hydrocarbons produce carbon and carbon monoxide?

carbon monoxide:

- not enough oxygen means that when the carbon reacts, there isn't enough oxygen to produce CO2, so it produces CO (carbon monoxide) instead

carbon:

- not enough oxygen means taht some of teh fuel doesn't burn so carbon and unburnt fuel are released (as soot)

how does carbon monoxide behave as a toxic gas?

Carbon monoxide is a colourless and odourless gas, which, breathed in, prevents red blood cells from carrying oxygen around the body which leads to death

what are the problems caused by incomplete combustion in appliances that use carbon compounds as fuel?

carbon monoxide causes health problems (e.g. carbon monoxide poisoning)

soot causes global dimming

How do impurities in some hydrocarbon fuels lead to the production of sulfur dioxide?

Most hydrocarbon fuels may also contain sulfur as an impurity

When the fuels are burnt in oxygen, this sulfur can combust to form sulfur dioxide

how is acid rain formed?

When sulfur dioxide reacts with the water vapour in the clouds, it forms sulfur hydroxide and falls back down as acid rain

problems associated with acid rain

- Damages buildings and statues as limestone dissolves

- Reduces the growth/kills trees and crops

- Lowers pH of water in lakes, killing fish

explain why, when fuels are burned in engines, oxides of nitrogens are produced

- nitrogen and oxygen from the air combine in the engine of a car to produce nitrogen monoxide

- when this nitrogen monoxide is released back into the air, it further reacts to form nitrogen dioxide

- nitrogen monoxide and nitrogen dioxide are pollutants

advantages of using hydrogen instead of petrol as a fuel for cars

- releases more energy per kilogram

- renewable resource, unlike petrol which is a fossil fuel (finite)

disadvantages of using hydrogen instead of petrol as a fuel for cars

- expensive to produce

- difficult and dangerous to store

- the production of hydrogen releases carbon dioxide (greenhouse gas)

petrol, kerosene and diesel oil are...

...non renewable fossil fuels obtained from crude oil

methane is a...

...non renewable fossil fuel found in natural gas

what is cracking?

the breaking down of larger, saturated hydrocarbon molecules (alkanes) into smaller, more useful ones, some of which are unsaturated (alkenes)

what does the cracking process involve?

the cracking process involves heating the hydrocarbons to vapourise them.

the vapours are either:

- passed over a hot catalyst

- or mixed with steam and heated to a very high temperature so that thermal deconposition reactions can occur

why is cracking necessary?

the demand for shorter-chained fractions outstrips the supply so cracking is necessary to convert surplus unwanted, longer-chained fractions into shorter, more useful ones

what type of reaction is cracking?

endothermic

what formed the earth's early atmosphere?

intense volcanic activity that released gases

what did the earth's early atmosphere contain?

- little or no oxygen

- a large amount of carbon dioxide

- water vapour

- small amounts of other gases

how did condensation of water vapour form oceans?

- when the earth cooled, the water vapour in the ear condensed and fell to the surface of the earth, forming oceans

how did the amount of carbon dioxide in the atmosphere decrease?

- when oceans were formed, large amounts of CO2 dissolved in the oceans

- carbonates precipitated in the ocean which sea creatures used up to make their shells and skeletons

- green plants and algae evolved, absorbing considerable amounts of CO2 during photosynthesis

how did the amount of oxygen in the early atmosphere gradually increase?

- primitive plants and algae began photosynthesizing which converted carbon dioxide from the atmosphere into oxygen

- as more plants began to appear, more oxygen was released, gradually increasing the air's composition

chemical test for oxygen

if oxygen is present, a glowing splint will relight

describe the greenhouse effect

- when shortwave radiation from the sun strikes the earth's surface it is absorbed, and re-emitted as infrared radiation

- when it is re-emitted, much of the radiation gets trapped inside the atmosphere by greenhouse gases which absorb the heat

- increasing levels of greenhouse gases mean that more heat is trapped, causing global warming--> enhanced greenhouse effect

greenhouse gas examples

carbon dioxide, water vapour, methane

what evidence is there for climate change?

the correlation between:

- the change in atmospheric carbon dioxide concentration

- the consumption of fossil fuels

- with temperature change

what makes this evidence of climate change less reliable?

the inaccuracies caused by:

- historical data

- fewer locations

composition of today's atmosphere

78% nitrogen

21% oxygen

0.04% carbon dioxide

small percentages of other gases

human activities that can cause climate change

burning fossil fuels

livestock farming

effects of burning fossil fuels

- caused by increased: energy usage, driving etc

- increased amount of greenhouse gases released into the atmosphere

- causes global warming and climate change

--> melting of polar ice caps, rising sea levels, flooding, wildfires

effects of increased livestock farming

causes deforestation and more methane

deforestation=

- increase of CO2 in atmosphere as there are less plants to photosynthesise it

more methane=

- greenhouse gas so leads to climate change and global warming

how can climate change be mitigated?

- use renewable energy instead of fossil fuels, like wind or solar power

- increased awareness to reduce energy usage

- governments are switching to greener energy sources

- financial incentives to companies to 'go green'

how can the effects of climate change be mitigated?

- construct flood defence systems

- build effective irrigation to combat drought

- develop new farming methods to adapt to the new climate