Gas Laws
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this presentation contains Boyle's law, Charles's law, Avogadro's law, ideal gas equation, units of gas constant R and significance of PV=nRT
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Gas Laws
- 1. 1
- 2. Gas Pressure in the light of KMT β’ Pressure is defined as the force the gas exerts on a given area of the container in which it is contained. π = πΉ π΄ 2
- 3. Units of Pressure β’ SI unit of pressure is Pascal P = π π2 = ππ β’ A Pascal is defined as the force of 1 Newton (N) spread over an area of 1 m2 β’ OTHER UNTIS: β’ 1 atm = 101325 Pa = 101325 Nm-2 β’ 1 atm = 101.325 KPa β’ 1 atm = 14.7 Psi (Pounds per square inch) β’ 1 atm = 760 torr = 760 mm of Hg β’ 1 J = 1 Nm = 107ergs = 1 Kgm2s-2 β’ 1 Cal = 4.18 J β’ 1 atm = 1.01325 bar 3
- 4. Effect of change in Pressure on the Volume of a Gas β Boyleβs Law Pressure and volume are inversely related at constant temperature. π β 1 π π = πΎ π ππ = πΎ π1 π1 = πΎ π2 π2 = πΎ π1 π1 = π2 π2 4 βFather of Modern Chemistryβ Robert Boyle
- 5. Boyleβs Law: P1V1 = P2V2
- 6. Boyleβs Law β Isotherms β’ When P of a gas is plotted againstV at different temperature, hyperbola curves are obtained which are called Isotherms. β’ As the temperature increases, the isotherms goes away from both the axis.This is due to increase in volume at higher temperature. 6
- 7. Effect of change in Temperature on the Volume of gas β Charlesβs Law β’ At constant Pressure, volume of given mass of a gas increase or decreases by decreases by 1/273 times of its original original volume at 0oC for every 1oC rise 7 Jacques-Alexandre Charles
- 8. Charlesβ Law: V1/T1 = V2/T2
- 9. Derivation of Critical Form of Charlesβs Law β’ Suppose the volume of a gas at 0oC =Vo β’ Volume at 1oC = ππ = ππ + ππ 1 273 β’ Volume at 2oC = ππ = ππ + ππ 2 273 β’ Volume at toC = ππ‘ = ππ + ππ π‘ 273 ππ‘ = ππ 1 + π‘ 273 ππ‘ = ππ 273+π‘ 273 π‘ + 273 = π πΎπππ£ππ ππππππππ‘π’ππ ππ‘ = ππ π 273 ππ‘ = ππ 273 π 9
- 10. Charlesβs law - Isobar When volume of gas is plotted against temperature at different pressures, a straight line is obtained. Each constant pressure line is called Isobar. 10
- 11. Absolute Zero β’ According to Charlesβs law: At constant Pressure, volume of given mass of a gas increase or decreases decreases by 1/273 times of its original volume at 0oC 11
- 12. Absolute Zero β’ According to Charlesβs law: At constant Pressure, volume of given mass of a gas increase or decreases decreases by 1/273 times of its original volume at 0oC 12
- 13. Absolute Zero β’ At exact -273 oC the volume of a given mass of gas reduces to zero. β’ -273oC = 0K β’ The temperature at which the given volume of a gas reduces to Zero is called Absolute Zero i.e. 0K or -273oC. β’ Actually all the gases liquefy or solidify before they reach -273oC. β’ This temperature is considered to as the lowest possible temperature 13
- 14. Avogadroβs Law β’ At constant temperature and pressure, the volume of a gas is directly related to the number of moles. π β π π = πΎπ π1 π1 = π2 π2 14 Amedeo Avogadro
- 16. Avogadroβs Law β Molar Volume β’ It has been calculated that if we have 1 dm3 of H2 gas, its mass at STP will be 0.09 g β’ β΄ 0.09 g H2 at STP = 1 dm3 β’ 2.016 g of H2 at STP = 1 0.09 Γ 2.106 = 22.414 ππ3 β’ 2.016 g H2 = 1 mol β’ Hence 1 mol H2 at STP will occupy volume 22.414 dm3 β’ This volume is called Molar volume. 16
- 17. Avogadroβs Law β’ Equal volumes of all gases at same temperature and pressure must contains equal number of molecules 17
- 18. Ideal Gas Equation β’ An equation that shows the effect of simultaneous changes in pressure and temperature on the volume of a given gas is called Ideal Gas equation. β’ Ideal gas equation is the combination of three gas laws: β’ Boyleβs Law β’ Charlesβs Law β’ Avogadroβs Law 18
- 19. Derivation of Ideal Gas Equation β’ According to Boyleβs law: π β 1 π β¦ . . (π) β’ According to Charlesβs law: π β π β¦ . . (ππ) β’ According to Avogadroβs law: π β π β¦ . . (πππ) β’ Combining equations (i) (ii) and (iii) we get: π β ππ π π = ππ π π ππ = ππ π Where R is called General Gas constant. β’ If n=1, then PV = RT or ππ π = π β’ So, π1 π1 π1 = π β’ And π2 π2 π2 = π β’ β΄ π1 π1 π1 = π2 π2 π2 19
- 20. Significance of Ideal Gas Equation β’ Calculation of Molecular mass of gas: ππ = ππ π π = π π Where W = mass of gas and M= Molecular mass ππ = π π π π πππ = ππ π π = ππ π ππ β’ Calculation of Density of gas: ππ = π π π π ππ = π π π π As π π = π ππ = ππ π π = ππ π π 20