C20 Unit 02 - Gases Short

Chemistry 20 – Unit 2 – Gases Lesson 1: Introduction By the end of this Unit you will be able to: – explain molecular behaviour, using models of the gaseous state of matter.

By the end of this Lesson you will be able to: – express pressure in a variety of ways, including units of kilopascals, atmospheres and millimetres of mercury. 20–B1.4k – perform calculations, based on the gas laws, under STP, SATP and other defined conditions. 20–B1.4k – explain that the goal of science is knowledge about the natural world 20–B1.2sts

Chemistry 20 – Unit 2 – Gases - The three states of matter include solid, liquid and gas. - The states of matter can be differentiated by the following:

State Solids

Characteristics Definite shape and definite volume

Liquids

Varied shape and definite volume

Gases

Varied shape and varied volume

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Gases in the Atmosphere - Gases in our atmosphere perform a major function in sustaining life on our planet. The atmosphere is needed for: - breathing and cellular respiration - C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(g) - photosynthesis in plants - 6 CO2(g) + 6 H2O(g) → C6H12O6(s) + 6 O2(g) - protection from harmful solar radiation such as ultraviolet light (UV rays) - transmission of heat and water vapour throughout the earth

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Composition of Gases in the Atmosphere

Gas nitrogen ( N2(g) ) oxygen ( O2(g) ) argon ( Ar(g) ) carbon dioxide ( CO2(g) ) neon ( Ne(g) ) helium ( He(g) ) krypton ( Kr(g) ), xenon ( Xe(g) ), methane ( CH4(g) ), hydrogen ( H2(g) ) nitrogen oxides ( NO2(g), NO3(g) ) sulfur oxides ( SO2(g), SO3(g) ) water vapour

Percentage By Volume 78.1 20.9 0.93 0.03 0.002 0.0005 trace amounts trace amounts trace amounts trace amounts

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- Although nitrogen and oxygen gases make up about 99 % of our atmosphere, other gases are a source of pollution. For example: - SO2(g) and SO3(g) are called sulfur oxides and contribute to acid rain. - SO2(g) + H2O(g) → H2SO3(aq) sulfurous acid - NO(g) and NO2(g) are called nitrogen oxides and contribute to acid rain. - NO(g) + H2O(g) → HNO2(aq) nitrous acid - CO(g) is given off in incomplete hydrocarbon combustion reactions.

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