Gases change volume (either get bigger or smaller) when there is a change in either temperature or pressure. The standard temperature and pressure that is used to compare different gasses is called STP.
1 STP is equal to 1 atmosphere of pressure and is at a temperature of 0ºC, which is the equivalent to 273.15ºK or 32ºF.
It is also known that at STP on mole of any gas takes up 22.4L of space.
Example:
Calculate the volume occupied by 8.10g of O2 at STP.
STEP 1: calculate molar mass of O2.
O=16 x 2 = 32g/mol.
O=16 x 2 = 32g/mol.
STEP 2: find # of moles.
8.10g O2 x 1mole = 0.253125 moles
8.10g O2 x 1mole = 0.253125 moles
32g
STEP 3: find the molar volume given that 1 mole of gas is equal 22.4L.
0.253125 moles x 22.4L = 5.67L
0.253125 moles x 22.4L = 5.67L
1mole
8.10g of O2 at STP = 5.67L of O2.
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