2 3 gases in the atmosphere

The most abundant gas in the earth's atmosphere is nitrogen.

False. Oxygen makes up 20% of the earth's atmosphere, with nitrogen making up 80%.

False. The proportion of gases in the air has not changed much in 200 million years.

The approximate percentage of nitrogen in the air is 78-80%.

Scientists know the historic composition of the air by analysing tiny air bubbles trapped in ice cores taken at the poles.

Combustion is the process of burning a substance in oxygen.

True. Combustion reactions can also be classified as oxidation reactions as the elements in the fuel react with oxygen.

The balanced symbol equation equation for the combustion of magnesium is: 2Mg (s) + O2 (g) → 2MgO (s)

The term exothermic relates to a chemical reaction that releases heat energy.

Combustion reactions are exothermic because they give out heat energy.

The word equation for the combustion of sulfur is: sulfur + oxygen → sulfur dioxide

Two observations you would make when magnesium undergoes combustion are:

Thermal decomposition is the break down of a substance using heat.

During the thermal decomposition of metal carbonates, the metal carbonate decomposes on heating to produce the metal oxide and carbon dioxide gas.

The general equation for the thermal decomposition of metal carbonates is: metal carbonate → metal oxide + carbon dioxide

The word equation for the thermal decomposition of copper(II) carbonate is: copper(II) carbonate → copper oxide + carbon dioxide

The balanced symbol equation for the thermal decomposition of copper(II) carbonate is: CuCO3 (s) →  CuO (s) + CO2  (g)

A test that could be used to identify the carbon dioxide gas produced during thermal decomposition is to bubble the gas through limewater and it should turn cloudy.

The observations which could be made when copper(II) carbonate undergoes thermal decomposition are that the green copper(II) carbonate powder darkens to form black copper(II) oxide.

True. Making cement releases CO2 when calcium carbonate is turned into calcium oxide.

Three greenhouse gases are carbon dioxide, water vapour and methane.

The greenhouse effect refers to greenhouse gases in the atmosphere absorbing and trapping infrared radiation emitted from the Earth's surface, causing warming.

The environmental effect of the increased amount of greenhouse gases in the atmosphere is climate change / global warming.

Two activities which release carbon dioxide into the atmosphere are:

It gets absorbed and trapped by greenhouse gases in the atmosphere.

The greenhouse effect maintains a suitable average global temperature. The enhanced greenhouse effect refers to increased warming due to higher levels of greenhouse gases.

The type of radiation from the sun which gets absorbed and re-emitted as infrared by the Earth's surface is long wavelength radiation / UV.

False. Energy from the sun is absorbed and re-emitted at longer wavelengths in the form of infrared radiation.