Calculate the volume of hydrogen required for complete hydrogenation of 0.25 #dm^3# of ethyne at STP?
However, an interesting thing takes place when you're dealing with gases that are under the same conditions for pressure and temperature. In such cases, the mole ratio becomes the volume ratio.
The idea is that, since you're dealing with two ideal gases, you can use the ideal gas law equation to write
The pressure and the temperature are the same for both gases, since the reaction presumably takes place at STP.
If you divided these two equations, you'll get
This is equivalent to
The mole ratio is equivalent to the volume ratio.
All you need now is the balanced chemical equation for the reaction, which looks like this
Notice that you have a
This translates into volumes as well. In other words, the volume of hydrogen gas must be twice as big as the volume of ethyne.