Volumes of Gases

• The number of molecules in one mole of gas is always 6 x 10²³ (Avagadro's constant).
• The molecules of a gas are extremely spread out, and so the size of them is negligible compared to the total volume the gas occupies.
• So one mole of gas always occupies the same volume, and at standard conditions (1 atmosphere, 298K) that volume is 24dm³.

• We can use this idea of molar volumes to work out the volumes of gases involved in a chemical reaction. For example, Ammonia is produced from Hydrogen and Nitrogen:
  
  N_2(g) + 3H_2(g) 2NH<sub>3
  
  From the equation, 1 mole of Nitrogen reacts with 3 moles of Hydrogen to produce 2 moles of Ammonia.
  
  So, using this idea:
  
  (1 x 22.4dm³) N2(g) + (3 x 22.4dm³) H2(g) (2 x 22.4dm³) NH3(g)
  
  So if we had 10dm³ of Nitrogen, it would react with 30dm³ of Hydrogen to form 20dm³ of Ammonia (standard conditions).</sub>

Useful books for revision:

Revise AS Chemistry for Salters (Written by experienced examiners and teachers of Salter's chemistry)
Revise AS Chemistry for Salters (OCR) (Salters Advanced Chemistry)

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