C1- crude oils and fuels Flashcards Preview

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Flashcards in C1- crude oils and fuels Deck (30)
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1
Q

What is crude oil?

A

Crude oil forms naturally over millions of years from the remains of living things. Most of the compounds in crude oil are hydrocarbons.

2
Q

What are hydrocarbons?

A

These are compounds that contain hydrogen and carbon atoms only, joined together by chemical bonds called covalent bonds.

3
Q

What are alkanes?

A

The alkanes are a family of hydrocarbons that share the same general formula. This is:

CnH2n+2 (small n’s and 2’s)

The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two.

4
Q

What are displayed formulas?

A

Alkane molecules can be represented by displayed formulas. In a displayed formula, each atom is shown as its symbol (C or H) and each covalent bond by a straight line.

5
Q

Alkanes are saturated hydrocarbons. What does this mean?

A

his means that their carbon atoms are joined to each other by single bonds. This makes them relatively unreactive, apart from burning or combustion, which is their reaction with oxygen in the air.

6
Q

Name the first four alkanes and their molecular formula:

A
methane	CH4 (small 4)
ethane	C2H6 (small numbers)
propane	C3H8 (small numbers)
butane	C4H10 (small numbers)
7
Q

What is distillation?

A

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. Distillation is commonly used to separate ethanol (the alcohol in alcoholic drinks) from water.

8
Q

Describe the distillation process to seperate ethanol from water.

A

The mixture is heated in a flask. Ethanol has a lower boiling point than water so it evaporates first. The ethanol vapour is then cooled and condensed inside the condenser to form a pure liquid.
The thermometer shows the boiling point of the pure ethanol liquid. When all the ethanol has evaporated from the solution, the temperature rises and the water evaporates.

9
Q

What is fractional distillation?

A

Fractional distillation is different from distillation in that it separates a mixture into a number of different parts, called fractions. A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.

10
Q

How does fractional distillation work for crude oil?

A

The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms. Note that the gases leave at the top of the column, the liquids condense in the middle and the solids stay at the bottom.

11
Q

What happens as you go up the fractionating column?

A

Hydrocarbon with smaller molecules condense at the top, which have the properties of:
lower boiling points
lower viscosity (they flow more easily)
higher flammability (they ignite more easily).
Which makes them better fuels.

12
Q

Why does complete combustion happen?

A

Fuels burn when they react with oxygen in the air. If there is plenty of air, complete combustion happens.

13
Q

What happens during complete combustion with carbon (equation)?

A

During complete combustion, carbon is oxidised to carbon dioxide:
carbon + oxygen → carbon dioxide

14
Q

What happens during complete combustion to hydrocarbon fuels (equations)?

A

Hydrocarbon fuels contain carbon and hydrogen. During combustion, hydrogen is oxidised to water. In general:
hydrocarbon + oxygen → carbon dioxide + water

15
Q

Why does incomplete combustion happen?

A

If there is insufficient air for complete combustion, incomplete combustion (also called partial combustion) happens.

16
Q

What happens during incomplete combustion?

A
Hydrogen is still oxidised to water, but carbon monoxide forms instead of carbon dioxide. Carbon monoxide is a toxic gas, so adequate ventilation is important when burning fuels.
Hydrogen (arrow) Water + Carbon monoxide
Solid particles (particulates) are also released.
17
Q

What is the problem with incomplete combustion?

A

Produces carbon monoxide which is toxic. And releases particulates. These contain carbon and are seen as soot or smoke. Particulates cause global dimming. They reduce the amount of sunlight reaching the Earth’s surface.

18
Q

What are the two main causes of acid rain?

A

Nitrogen oxides and sulfur dioxide.

19
Q

How is sulfur dioxide produced?

A

Coal and most hydrocarbon fuels naturally contain some sulfur compounds. When the fuel burns, the sulfur it contains is oxidised to sulfur dioxide:
sulfur + oxygen → sulfur dioxide
This gas dissolves in water to form an acidic solution. It is a cause of acid rain.

20
Q

What is the problem with acid rain?

A

Acid rain reacts with metals and rocks such as limestone, causing damage to buildings and statues. Acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.

21
Q

How can you reduce sulfur dioxide in the air?

A

Sulfur can be removed from fuels before they are used. ‘Low sulfur’ petrol and diesel are widely available at filling stations to use in vehicles. In power stations, sulfur dioxide can be removed from the waste gases before they are released from chimneys. The waste gases are treated with powdered limestone. The sulfur dioxide reacts with it to form calcium sulfate. This can be used to make plasterboard for lining interior walls,.

22
Q

How are oxides of nitrogen produced?

A

At the high temperatures found in an engine or furnace, nitrogen and oxygen from the air can react together. They produce various oxides of nitrogen, often called NOx. These also cause acid rain.

23
Q

What chemical formula is typically used for the various oxides of nitrogen?

A

NOx (small x)

24
Q

What are biofuels?

A

Biofuels are fuels produced from plant material. They have some advantages and disadvantages compared to fossil fuels.

25
Q

What is biodiesel made from and how can it be used?

A

Biodiesel is made from rapeseed oil and other plant oils. It can be used in diesel-powered vehicles without needing any modifications to the engine.

26
Q

What is the chemical equation for ethanol and why isn’t it a hyrdocarbon?

A

Ethanol, C2H5OH, is not a hydrocarbon because it contains oxygen as well as hydrogen and carbon

27
Q

How is bioethanol made and how can it be used?

A

Bioethanol is made by fermenting sugars from sugar cane, wheat and other plants. It cannot be used on its own unless the engine is modified. However, modern petrol engines can use petrol containing up to 10 percent ethanol without needing any modifications, and most petrol sold in the UK contains ethanol.

28
Q

What are the ethical issues of biofuels?

A

Food that could be used to feed people is being used on fuel
could lead to food shortages
more land is taken up
increase the price of food

29
Q

What are the economical issues of biofuels?

A

human resources -more people are needed to produce biofuels than are needed to produce petrol and diesel
increased income - for farmers
lower fuel prices - biofuels limit the demand for fossil fuels, helping to reduce increases in fuel prices.

30
Q

What are the environmental issues of biofuels?

A

Biodiesel naturally contains little sulfur. For example, it may be said that they are carbon neutral – the amount of carbon dioxide released when they are used is the same as the amount absorbed by the plants as they grew. If so, this would reduce the production of this greenhouse gas. However, while biofuels produce less carbon dioxide overall, they are not carbon neutral. This is because fossil fuels are used in their production, for example in making fertilisers for the growing plants.

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