Answer : The original volume of gas is [tex]365cm^3[/tex]
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 = 800 torr
[tex]P_2[/tex] = final pressure of gas at STP = 760 torr
[tex]V_1[/tex] = initial volume of gas = ?
[tex]V_2[/tex] = final volume of gas at STP = [tex]450.0cm^3[/tex]
[tex]T_1[/tex] = initial temperature of gas = [tex]-40^oC=273+(-40) =233K[/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{800torr\times V_1}{233K}=\frac{760torr\times 450.0cm^3}{273K}[/tex]
[tex]V_1= 364.8cm^3\approx 365cm^3[/tex]
Therefore, the original volume of gas is [tex]365cm^3[/tex]
