chemistry specification part 6

Question 1

what is cracking

Answer 1

turn long saturated (alkane) molecules into smaller unsaturated(alkene) molecules (which are more useful)

Question 2

how does cracking happen and why are longer molecules broken down

Answer 2

form of thermal decomposition where a substance breaks down into at least two new ones when you heat it. This breaks strong covalent bonds which need lots of energy. A catalyst is usually added. Longer molecules made from fractional distillation are broken down smaller to make products like petrol as they have a higher demand.

Question 3

how do you crack??????????????????

Answer 3

heat the alkane until it vaporises.This will break down once it comes into contact with the catalyst (aluminium oxide) producing alkenes

Question 4

recall the earth’s early atmosphere phase 1

Answer 4

little or no oxygen
a large amount of carbon dioxide from volcanoes erupting
water vapour from steam caused by erupting volcanoes later condensed to form oceans
small amounts of other gases

Question 5

what is phase 2 of the earth’s early atmosphere

Answer 5

nitrogen gas was formed by ammonia reacting with oxygen and was released by denitrifying bacteria. Nitrogen is unreactive so it increased in the atmosphere because it was being made but not broken down. green plants evolved and removed co2 through photosynthesis and expelled oxygen. Oxygen built up in the air and carbon was locked up in fossil fuels and sedimentary rocks

Question 6

what is phase 3 of the earths early atmosphere

Answer 6

oxygen created the ozone layer which blocked harmful rays from the sun and enabled more complex organisms to evolve. There was no co2 left then.

Question 7

what are greenhouse gases

Answer 7

gases in the atmosphere that absorb heat and reflect heat radiation.Carbon dioxide,methane and water vapour are greenhouse gases

Question 8

what is the greenhouse gas effect

Answer 8

1. the earth radiates the heat radiation it absorbs as longer infrared wavelengths. Some of this is absorbed by greenhouse gases
2. some of the infrared radiation is re-emitted back towards the earth by greenhouse gases and some of it is emitted into space
3. the absorption and re-emission of infrared by greenhouse gases is what keeps the Earth warm

Question 9

what is global warming

Answer 9

a type of climate change where the earth’s temperature increases due to greenhouse gases

Question 10

what is climate change

Answer 10

long term shifts in weather and temperature patterns