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Chemistry❌ > SC20-21 > Flashcards

SC20-21 Flashcards

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1
Q

What is crude oil separated into?

A

Different hydrocarbon fractions

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2
Q

What is the main source of hydrocarbons?

A

Crude oil

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3
Q

How is crude oil formed?

A

It’s formed underground, over millions of years (at high temperatures and pressures) from the buried remains of plants and animals.

It’s non-renewable (finite), so one day it will run out.

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4
Q

What is crude oil?

A

It’s a complex mixture of lots of different hydrocarbons

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5
Q

What is a hydrocarbon?

A

It’s compounds which contain just hydrogen and carbon.

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6
Q

What is the formations of hydrocarbons in crude oil?

A

They have their carbon atoms either arranged in rings or chains.

They’re mostly alkanes.

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7
Q

What are fractions?

A

Simpler, more useful mixtures containing groups of hydrocarbons.

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8
Q

How is crude oil separated into different fractions?

A

Fractional distillation.

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9
Q

what happens in fractional distillation?

A

The oil is heated until most of it has turned to gas. The gases enter a fractionating column.

In the column there’s a temperature gradient. (Its hot at the bottom and gets colder at the top).

The longer hydrocarbons have higher boiling points. They turn back into liquids and drain out of the column early on, when they’re near the bottom. And the shorter hydrocarbons have lower boiling points so drain out nearer the top.

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10
Q

Name the different fractions?

A

Bottom to top -

Bitumen 
Fuel
Diesel
Kerosene 
Petrol
Gases
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11
Q

What are the uses for -

Bitumen 
Fuel
Diesel
Kerosene 
Petrol 
Gas
A
  1. Surface roads and roofs.
  2. Fuel for large ships and also some power stations.
  3. Fuel in some cars and larger vehicles (trains).
  4. Aircrafts
  5. Cars
  6. Domestic heating and cooking.
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12
Q

What are homologous series?

A

Its a group (family) of molecules which have the same general formula and share similar chemical properties.

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13
Q

Name two different homologous series?

A

Alkanes

Alkenes

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14
Q

Name some hydrocarbons? (Alkanes)

How many carbons are in each of them?

A 
1 - methane 
2 - ethane 
3 - propane 
4 - butane 
5 - pentane 
6 - hexane
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15
Q

What’s the general formula for alkanes?

A

CnH2n+2

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16
Q

Why do hydrocarbons make good fuels?

A

Because the combustion reactions that happen when you burn them in oxygen gives out lots of energy.

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17
Q

What are the products when you burn hydrogen in plenty of oxygen?

A

Carbon dioxide and water.

This is called complete combustion.
Incomplete combustion occurs when a hydrocarbon burns in a limited supply of oxygen.

18
Q

When does incomplete combustion happen?

A

When hydrocarbons burn in a limited supply of oxygen.

19
Q

What does an incomplete combustion produce?

A

Toxic carbon monoxide and soot

20
Q

Why is carbon monoxide toxic?

A

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 supply tot eh brain can lead to fainting, a coma or even death.

21
Q

What does soot do?

A

Tiny particles of carbon can be released into the atmosphere. When they fall back to the ground, the deposit themselves as the horrible black dust we call soot.

Soot makes buildings look dirty, reduces it quality and can cause or worsen respiratory problems.

22
Q

What does sulphur dioxide cause?

A

Acid rain.

23
Q

How does sulphur dioxide cause acid rain?

A

Sulfur dioxide comes from suffer impurities in the fossil fuels.

When sulfur dioxide mixes with clouds, it forms dilute sulfuric acid. This then falls as acid rain.

24
Q

What can acid rain do?

A

Causes lakes to become acidic and many pants and animals die as a result.
Kills trees, damages limestone buildings and stone statues and can also make metal corrode.

25
Q

How are nitrogen oxides created?

A

From a reaction between nitrogen and oxygen in the air, caused by the energy released by combustion reactions, for example in the internal combustion engines of cars.

26
Q

What do nitrogen oxides cause?

A

They’re harmful pollutants.

They can contribute to acid rain and, at ground level, can cause photochemical smog.

27
Q

What is photochemical smog?

A

Its a type of air pollution that can cause breathing difficulties, headaches and tiredness.

28
Q

What are the pros of using hydrogen as a fuel?

A

Its a very clean fuel.
The only waste product is water as the hydrogen reacts with oxygen.
Hydrogen is obtained from water which is a renewable resource, so it wont run out.

29
Q

What are the cons of using hydrogen as a fuel?

A

You need a special expansive engine.
Needs to be manufactured which is expensive and often uses energy from another source (fossil fuels).
Its hard to store so isn’t widely available.

30
Q

What is cracking?

A

Splitting up long chain hydrocarbons.

31
Q

What does cracking do?

A

Turns long saturated (alkane) molecules into smaller unsaturated (Alkene) and alkane molecules (which are more useful).

Its a form of thermal decomposition

32
Q

What is thermal decomposition?

A

One substance breaks down into at least two new ones when you heat it. This means breaking strong covalent bonds, so you need lots of energy.

A catalyst is often added to speed things up.

33
Q

What is the theory for how the atmosphere has evolved?

A

Phase 1 - volcanoes gave out steam and CO2.

Phase 2 - green plants evolved and produced oxygen.

Phase 3 - ozone layer allows evolution of complex animals.

34
Q

What is phase 1 of the atmosphere?

A

The wrath’s surface was originally molten for many millions of years. There was almost no atmosphere.

Eventually the earths surface cooled and a thin crust formed, but volcanoes kept erupting, releasing gases from inside the earth. It released mainly CO2.

When things eventually settled down, the early atmosphere was mostly CO2, and water vapour. There was very little oxygen.

The water vapour later condensed to form the oceans.

35
Q

What is phase 2 of the atmosphere?

A

A lot of the early CO2 dissolved into the oceans.

Nitrogen gas was then put into the atmosphere in two ways - it was formed by ammonia reacting with oxygen, and was released by bacteria.

Nitrogen wasn’t very reactive. So the amount of N2 in the atmosphere increased, because it was being made but not broken down.

Next, green plants evolved over most of the earth. As they photosynthesised, they removed CO2 and produced oxygen.

Due to the plants the amount of oxygen in the air gradually increased and much of the CO2 eventually got locked up in fossil fuels and sedimentary rocks.

36
Q

What is phase 3 of the atmosphere?

A

The build up of oxygen in the atmosphere killed off early organisms that couldn’t tolerate it, but it did allow the evolution of more complex organisms that made use of the oxygen.

The oxygen also created the ozone layer, which blocked harmful rays from the sun and enabled vein more complex organisms to evolve.

There is virtually no CO2 left now.

37
Q

How is human activity affecting the composition of air?

A

CO2 levels are increasing.

  1. The human population is increasing, so there is more people respiring, giving out CO2.
  2. Mor people means that more energy is being used (heating, lighting).
  3. More people also means more more land is needed to build houses and grow food. This space is often made by chopping down trees, which results in less things to take CO2 out of the atmosphere.
  4. CO2 is also produced by volcanoes erupting.
38
Q

How does the greenhouse effect help keep the earth warm?

A
  1. The sun gives out electromagnetic radiation.
  2. Some electromagnetic radiation, at most wavelengths, passes through the atmosphere.
  3. The ER with short wavelengths is absorbed by the earth - warming it.
  4. If the concentration of greenhouse gases in the atmosphere increases, you get an enhanced greenhouse effect. This is where more heat radiation from the earth is absorbed and less re-emitted back into space. This causes the atmosphere to heat up.
39
Q

Why is historical data not as accurate?

A

Less data was taken over fewer locations and the methods used to collect the data were less accurate.

40
Q

How can you estimate past data?

A

Analyse fossils, tree rings or gas bubbles trapped in ice sheets to estimate past levels of atmospheric carbon dioxide.

However they’re much less precise than current measurements and also much less representative of global levels.

Chemistry❌ (11 decks)

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