Crude Oil
Hydrocarbons are compounds that contain carbon and hydrogen only. Crude oil is a complex mixture of hydrocarbons containing molecules in which carbon atoms are in chains or rings. Crude oil is an important source of useful substances used in energy and petrochemical industries, but is a finite resource. Petrol, kerosene and diesel oil are non-renewable fossil fuels obtained from crude oil and methane is a nonrenewable fossil fuel found in natural gas
Hydrocarbons in crude oil are separated into simpler, more useful mixtures by fractional distillation due to the variation of boiling points. This happens in a fractioning column. Hot cruel oil vapours are piped into the bottom, where the column is hottest. The vapours rise through the column and cool down, condensing when they reach the section where the column is cool enough, where the liquid falls onto a tray and is piped away
- Molecule size increases down the column
- More intermolecular forces in larger molecules so boiling point increases down the column
- Longer chains also mean harder to ignite
- Longer hydrocarbons have higher viscosity
A homologous series is a series of compounds which have the same general formula and similar chemical properties. The series shows a gradual variation in physical properties, and each member differs from neighbouring compounds by CH2 in the molecular formula. Most compounds in crude oil belong to the alkane family
When crude oil is separated, the volume of each fraction does not match the volume that can be sold. The supply of some fractions is greater than customer demand, while the demand for other fractions is greater than the supply. Cracking is used to match supply and demand. Cracking involves breaking covalent bonds in hydrocarbon molecules. Vapours of a fraction are passed over an alumina catalyst and heated to 650°C, speeding up the reaction to break down these molecules. Smaller, useful molecules are made. Some of the products are alkanes, saturated molecules, and other products are unsaturated alkenes, with a double carbon bond. The total number of each atom stays the same and this can be used to predict the products.
Combustion
The complete combustion of hydrocarbon fuels is a reaction in which the only products are CO2 and water. Large quantities of energy are released during the exothermic reaction. Incomplete combustion occurs when a hydrocarbon burns in a limited supply of oxygen, which can produce carbon in the form of soot, as well as carbon monoxide.
Carbon monoxide is a toxic gas which combines with haemoglobin in red blood cells, preventing oxygen combining and reducing the blood concentrations of oxygen, causing the person to feel sleepy or to lose consciousness. Severe CO poisoning can even cause death.
Incomplete combustion can cause problems in appliances that use hydrocarbon fuels, such as heaters and boilers. Soot can block the pipes carrying away waste gases from the appliance. Soot also blackens the building and can cause respiratory issues if it collects in the lungs
When fossil fuels are burnt, other harmful gases are produced alongside carbon dioxide, mainly sulfur dioxide and nitrogen oxides. SO2 comes from sulfur impurities in fossil fuels. When it mixes with rain, it forms dilute sulfuric acid which then falls as acid rain. Acid rain causes lakes to become acidic, and many organisms die as a result. Acid rain kills trees, damages limestone buildings and stone statues and also causes the corrosion of metals.
Nitrogen oxides are created from a reaction between nitrogen and oxygen in the air, caused by energy released by combustion reactions. They are harmful pollutants which can contribute to acid rain and photochemical smog, a type of air pollution that causes breathing difficulties.
Hydrogen fuel can be used to fuel cars. It is a by-product of cracking but can also be produced by reacting methane with steam. The combustion of hydrogen produces only water, meaning it is clean, and the water is renewable. Hydrogen is easily ignited. However, hydrogen is a gas at rtp, and therefore storage is difficult
Earth and Atmospheric Science
Gases produced by volcanic activity formed the Earth’s early atmosphere. It was thought to contain little or no oxygen, and large amounts of carbon dioxide, water vapour, methane and ammonia. Evidence for this comes from rocky planets with volcanoes like Venus and Mars which have high CO2 levels in their atmospheres. When the Earth cooled, water vapour in the atmosphere condensed to become water which formed the oceans. Large proportions of CO2 dissolved into the oceans so the levels in the atmosphere decreased considerably, and this gas was used by sea creatures to form shells made of calcium carbonate. Photosynthetic organisms began to develop, removing CO2 and adding O2 to the atmosphere, meaning the amount of oxygen gradually increased. Now, the atmosphere is 21% oxygen, which is important for aerobic respiration.
Pure oxygen will relight a glowing splint.
The Greenhouse Effect is when various gases in the atmosphere, including carbon dioxide, water and methane, absorb heat radiated from the Earth, subsequently releasing energy which helps keep the Earth warm
There is plenty of evidence that we may be causing climate change. We are each using more energy, population, and therefore demand for energy, is increasing, deforestation rates are still too high, and levels of carbon dioxide have continued to rise exponentially since the Industrial Revolution. Burning fossil fuels emits greenhouse gases, and growing livestock and rice paddy fields emits methane. Historic levels of gas can be found by analysing ice cores. Continuous data for temperature exists from 1880, but these data readings are not accurate due to the lower resolution of thermometers and the high chance of error. Also, the readings to not show global levels at a specific time.
Rising global temperatures will cause ice to melt, raising sea levels and increasing flooding. Organisms will become extinct as the change is too fast for them to adapt. Extreme weather events will increase in frequency. Coral bleaching may occur. These effects can be mitigated by limiting fossil fuel use and using renewables instead, global carbon capture schemes. To adapt to these changes, we can build irrigation systems and improve flood defences.