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# Ideal gases

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The grade 11 ideal gases presentation

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### Ideal gases

1. 1. 1Everything Science www.everythingscience.co.za7. Ideal gasesChemistryGrade 11
2. 2. 2Everything Science www.everythingscience.co.zaThe kinetic theory of gasesThe kinetic theory of gases helps to explain the behaviour of gases under differentconditions.The kinetic theory of gases states that gases are made up of constantly moving particles thathave attractive forces between them.From the kinetic theory of gases we can define the pressure and the temperature of a gas.The pressure of a gas is a measure of the number of collisions of the gas particles with eachother and with the sides of the container that they are in.The temperature of a substance is a measure of the average kinetic energy of the particles.
3. 3. 3Everything Science www.everythingscience.co.zaIdeal and real gasesAn ideal gas has identical particles of zero volume, with no intermolecular forces betweenthe particles. The atoms or molecules in an ideal gas move at the same speed.A real gas behaves like an ideal gas, except at high pressures and low temperatures. At lowtemperatures, the forces between molecules become significant and the gas will liquefy. Athigh pressures, the volume of the particles becomes significant.
4. 4. 4Everything Science www.everythingscience.co.zaSI UnitsThe SI unit of temperature is the Kelvin (K). Temperature in degrees Celsius (°C) can beconverted to temperature in Kelvin (K) using the following equation:The SI unit of pressure is the Pascal (Pa). The following conversions are useful:The SI unit of volume is the cubic metre (m³). The following conversions are useful:T K=TC+273760 mmHg=1atm=101 325 Pa1m3=1 000dm3=1 L
5. 5. 5Everything Science www.everythingscience.co.zaBoyles lawBoyle’s law states that the pressure of a fixed quantity of gas is inversely proportional to thevolume it occupies so long as the temperature remains constant.p1V1=p2V 2
6. 6. 6Everything Science www.everythingscience.co.zaCharles lawCharles’ law states that the volume of an enclosed sample of gas is directly proportional toits Kelvin temperature provided the pressure and amount of gas remains constant.V 1T1=V 2T2
7. 7. 7Everything Science www.everythingscience.co.zaPressure-temperature relationThe pressure of a fixed mass of gas is directly proportional to its temperature, if the volume isconstant.p1T1=p2T2
8. 8. 8Everything Science www.everythingscience.co.zaGeneral gas lawCombining Boyle’s law and the relationship between the temperature and pressure of a gas,gives the general gas equation, which applies as long as the amount of gas remains constant.The general gas equation is:p1 V1T1=p2V 2T2
9. 9. 9Everything Science www.everythingscience.co.zaAvogadros law and the universal gas constantAvogadro’s law states that equal volumes of gases, at the same temperature and pressure,contain the same number of molecules.The universal gas constant (R) is 8,314 J·K−1·mol−1. This constant is found by calculating pVfor 1 mol of any gas.
10. 10. 10Everything Science www.everythingscience.co.zaThe ideal gas lawExtending the above calculation to apply to any number of moles of gas gives the ideal gasequation:In this equation, SI units must be used. The SI unit for volume is m3, for pressure it is Paand for temperature it is K.pV =nRT
11. 11. 11Everything Science www.everythingscience.co.zaFor more practice see:www.everythingscience.co.zaShortcode: ESBP3