Topic 15 - States of Matter

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[edit] 15.1 Gases

[edit] 15.1.1

PV = nRT

  • P: Pressure in atm.
  • V: Volume in cm3.
  • n: Number of atoms in mols.
  • R: 82.05 cm3 atm K-1 mol-1 (the value is in the data book).
  • T: Temperature in K.

[edit] 15.1.2

The above equation can be rearranged as P1V1=P2V2 or V1/T1=V2/T2 if temperature or pressure are assumed to be constant.

Avogadro's law : Equal volumes of any gas contain equal numbers of particles. At 273K, 1 atm there is one mol per 22.4 dm3 (in the data book).

[edit] 15.1.3

Dalton's law of partial pressures : The partial pressure of a gas is the pressure the gas would exert if the gas were alone in its container.

If there are Gases A, B and C filling a dm3, b dm3 and c dm3 respectively then the partial pressure of a = (a)/(a+b+c) x total pressure.

[edit] 15.1.4

Pp = (number of molecules in the gas)/(total number of molecules) x total pressure

Note: Apparently, though it's never been in the syllabus, there have been questions on Van Der Wall's equation, which is an extension of PV=nRT for non-ideal gas situations. It is (P+an2/V2)(V-nb)=nRT, where a and b are constants for a given gas (which I assume would be given if necessary).

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