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Gas Stoichiometry


    Gas stoichiometry involves volumes of gases, with one mol of gas taking up a certain volume depending on the temperature and pressure.


STP --> Standard Temperature and Pressure
                OC and 101.3 kPa

*** 1 mol of any gas occupies 22.4 L of space.

SATP -->  Standard Ambient Temperature and Pressure
                    25C and 100 kPA

*** 1 mol of any gas occupies 24.8 L of space.

    Gas stoichiometry is basically the same thing as basic stoichiometric calculations, with the exception of possibly adding a step, depending on what the question is asking.

Example:
When 6.25 mol of butane burns with oxygen gass, what volume (in litres) of water vapour at SATP is produced?

 


C4H10  +  O2   --->   CO2  +  H20

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V

C4H10  +  13O2   --->   4CO2  +  5H20

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V

C4H10  +  13O2   --->   4CO2  +  5H20
6.25 mols                                            Xl

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V

There is no need to convert anything because we are working with mols; however, if it were 6.25 grams, we would need to convert the grams to mols.

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V

6.25 mols of C4H10 = 5 mols H2O
                                                                            ---------------- = 31.25 mols H2O
                                         1 mol C4H10

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31.25 mols H2O = 24.8 L
                                                                   --------------- = 775 L of H2O
                                   1 mol

This step, which in basic stoichiometry is usually converting mols to grams, is different in gas stoichiometry; we are now converting mols to liters. The question asks for SATP, so we know we use 24.8 L. If the question asked for STP the 24.8 L would be 22.4 L.