1.

At 1 atm pressure, 1 g of water having a volume of 1 cm^3 becomes 1671 cm^3 of steam when boiled. The heat of vaporization of water at 1 atm is 539 cal g^(-1) . What is the change in internal energy during the process?

Answer»

539 cal
417 cal
498.5 cal
835.5 cal

Solution :Heat spent during vaporisation is ,
Q=mL= 1 X 539 = 539 cal
`THEREFORE` Work DONE W=P `(V_v- V_l)`
`= 1.013xx10^5 XX(1671-1)xx10^(-6)` J
`=169.2/4.18` cal = 40.5 cal
`therefore` Change in INTERNAL energy
U=539 cal - 40.5 cal = 498.5 cal


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