Topic 8 - Fuels and Earth Science Flashcards
What are the problems associated with acid rain?
Acid rain causes lakes to become acidic and many plants and animals dies as a result. Acid rain kills trees, damages limestone buildings and stone statues and can also make metal corrode.
How did the amount of nitrogen increase in the atmosphere?
Nitrogen gas (N2) was then put into the atmosphere in two ways -it was formed by ammonia reacting with oxygen, and was released by denitrifying bacteria. N2 isn’t very reactive. So the amount of N2 in the atmosphere increased, because it was being made but not broken down
How are oxides of nitrogen produced when fuels are burned in engines?
High temperatures are reached when fuels are burned in engines. At these high temperatures, nitrogen and oxygen from the air can react together to produce oxides of nitrogen such nitrogen monoxide. Oxides of nitrogen are atmospheric pollutants. They can react in sunlight with other substances to produce a hazy, harmful smog - Photochemical smog. Nitrogen dioxide is toxic. It can cause bronchitis and other lung diseases. It also dissolves in water in the clouds, forming an acidic solution that contributes to acid rain.
What are hydrocarbons?
A compound with hydrogen and carbon only.
How do impurities in some hydrocarbon fuels result in the production of sulfur dioxide?
Many hydrocarbon fuels naturally contain sulfur impurities. When the fuels are burned, the sulfur oxidises to form sulfur dioxide gas. Sulfur dioxide dissolves in water in the clouds to form sulfurous acid: Oxygen in the air reacts with sulfurous acid to form sulfuric acid.
What did the early atmosphere contain?
The early atmosphere probably contained:
- little or no oxygen
- a large amount of carbon dioxide
- water vapour
- small amounts of other gases, such as ammonia and methane
How was the early atmosphere formed?
The Earth’s surface was originally molten for many millions of years. There was almost no atmosphere.
Eventually the Earth’s surface cooled and a thin crust formed, but volcanoes kept erupting, releasing gases from inside the Earth. This ‘degassing’ is mainly carbon dioxide, but also steam, methane and ammonia. When things finally settle down, the early atmosphere is mostly CO, and water vapor. There was very little oxygen
Describe the greenhouse effect
Infrared radiation from the Sun is only partly absorbed by the Earth. The rest is radiated into the atmosphere. Although some of the infrared radiation escapes, some is absorbed by greenhouse gases. This keeps the energy in the atmosphere, warming it up. This gradual warming of the atmosphere over many years is referred to as global warming.
How were oceans formed?
The water vapour in the atmosphere condensed to form oceans.
How did the growth of green plants increase oxygen levels and decrease CO2 levels?
Next, green plants evolved over most of the Earth. As they photosynthesised, they removed CO2 and produced O2. Thanks to the plants, the amount of O2 in the air gradually built up and much of the CO2 eventually got locked up in fossil fuels and sedimentary rocks.
What is the difference between alkanes and alkenes?
Alkanes and alkenes both form homologous series of hydrocarbons, but:
- alkanes are saturated (their carbon atoms are only joined by C-C single bonds)
- alkenes are unsaturated (they contain at least one C=C double bond)
As a result, alkenes are more reactive than alkanes. Alkenes can take part in reactions that alkanes cannot. For example, ethene molecules can react together to form poly(ethene), a polymer.
How does the size of the hydrocarbon determine its properties?
- The intermolecular forces of attraction break a lot more easily in small molecules than they do in bigger molecules. That’s because the forces are much stronger between big molecules than they are between small molecules. Even if a big molecule can overcome the forces attracting it to another molecule at a few points along its length, it’s still got lots of other places where the force is still strong enough to hold it place. That’s why big molecules have higher boiling points than small molecules do
- Shorter hydrocarbons are easy to ignite because they have lower boiling points, so tend to be gases at room temperature. These gas molecules mix with oxygen in the air to produce a gas mixture which bursts into flames if it comes into contact with a spark. Longer hydrocarbons are usually liquids at room temperature. They have higher boiling points and are harder to ignite.
- Viscosity measures how easily a substance flows. The stronger the force between hydrocarbon molecules, the harder it is for the liquid to flow. Fractions with longer hydrocarbons have a higher viscosity -they’re thick like treacle. Fractions made up of shortened hydrocarbons have a low viscosity and are much runnier.
What happens in incomplete combustion of hydrocarbons?
If there is not enough oxygen around for complete combustion , you get incomplete combustion. The products of incomplete combustion contain less oxygen. Water is still produced, but carbon monoxide and carbon (in the form of soot) are also produced. Less energy is released than during complete combustion.
What is supply and demand in cracking?
The supply is how much of a fraction an oil refinery produces. The demand is how much of a fraction customers want to buy. Fractional distillation of crude oil often produces more of the larger hydrocarbons than can be sold, and less of the smaller hydrocarbons than customers want.
Smaller hydrocarbons are more useful as fuels than larger hydrocarbons. Since cracking converts larger hydrocarbons into smaller hydrocarbons, the supply of fuels is improved. This helps to match supply with demand.
What is a homologous series?
A homologous series is series of compounds which:
- have the same general formula
- differ by CH2 in the molecular formula of neighbouring compounds
- show a gradual variation in physical properties, such as their boiling points
- have similar chemical properties
