Gas Stoichiometry
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# Gas Stoichiometry Shortcut

When an equation stoichiometry problem involves two gases at the same temperature and pressure, a different shortcut can be used. This shortcut employs the coefficients from the balanced equation to create a volume ratio that converts directly from volume of one gas to volume of another. The following hypothetical case illustrates the underlying logic.

Consider two gases, A and B, at the same temperature and pressure. The ratio of their volume to the moles of gas can be determined from the ideal gas equation.

If the two gases are at the same temperature and pressure, the V/n ratio for each gas must be the same.

if   T = TA = TB   and   P = PA = PB

If we rearrange the equation above, we see that the volume ratio of two gases at the same temperature and pressure is equal to their molar ratio.

The molar ratio of the two gases is constructed from the coefficients in the balanced equation. Because the molar ratio is equal to the volume ratio for gases at the same temperature and pressure, the coefficients from the balanced equation can also be used to generate a factor that converts directly from volume of one gas to volume of another, as in the following example.

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