GAS LAWS

COMBINED GAS LAW

• By combining Boyle's and Charles' Laws we arrive at the equation:
• P1 V1 / T1 = P2 V2 / T2
• Also knowing that the conditions for S.T.P. are 273K & 100kPa,
• We can substitute for P2 and T2
• i.e. P1 V1 / T1 = 100 kPa X V2 / 273 K

ADDING AVOGADRO'S HYPOTHESIS

• Avogadro postulated that 1 mole of any gas at S.T.P. occupied a volume of 22.41 L
• i.e. 1 mol = 22.4 L. Hence n moles = V L.
• Combining these two equations, we can then say that at S.T.P., V = 22.4 n L.
• This can also be substituted into our equation. Which now becomes :
• P V / T = 100kPa X (22.4 n ) / 273K

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