Question

CO(g) + 2 H2 --> CH3OH2.50 g of hydrogen is reacted with 30.0 L of carbon monoxide at STP. What is the volume of excess remaining in liters?

Answer 1

The first step to solve this question is to convert the mass of H2 to moles, using its molecular mass:

`2.50gH_2\cdot(molH_2)/(2.00gH_2)=1.25molH_2`

Now, convert the volume of CO to moles using the ideal gas law:

`PV=nRT`

Solve the equation for n and replace P, V, T and R for its known values (1atm, 30.0L, 0.082atmL/molK and 273.15K):

`\begin{gathered} n=(PV)/(RT) \\ n=(1atm\cdot30.0L)/(0.082atmL/molK\cdot273.15K) \\ n=1.34mol \end{gathered}`

From the given equation we can find how many moles of CO react with 1.25 moles of H2:

`1.25molH_2\cdot(1molCO)/(2molH_2)=0.625molCO`

Substract this amount to the value of n to find the excess remaining:

`1.34molCO-0.625molCO=0.715molCO`

Use the ideal gas law once again, but this time to find the volume occupied by 0.715moles of CO:

`\begin{gathered} V=(nRT)/(P) \\ V=(0.715mol\cdot0.082atmL/molK\cdot273.15K)/(1atm) \\ V=16.01L \end{gathered}`

It means that 16.01L of CO are remaining.