Answer : The volume of the hydrogen at STP is, 36.8 mL
Explanation :
Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law.
The combined gas equation is,
[tex]\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}[/tex]
where,
[tex]P_1[/tex] = initial pressure of gas = 751 torr
[tex]P_2[/tex] = final pressure of gas at STP = 760 torr
[tex]V_1[/tex] = initial volume of gas = 40.0 mL
[tex]V_2[/tex] = final volume of gas at STP = ?
[tex]T_1[/tex] = initial temperature of gas = [tex]20^oC=273+20=293K[/tex]
[tex]T_2[/tex] = final temperature of gas at STP = [tex]0^oC=273+0=273K[/tex]
Now put all the given values in the above equation, we get:
[tex]\frac{751torr\times 40.0mL}{293K}=\frac{760torr\times V_2}{273K}[/tex]
[tex]V_2=36.8mL[/tex]
Therefore, the volume of the hydrogen at STP is, 36.8 mL
