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Question: 1/2 mole of helium gas is contained in a container at S.T.P. The heat energy needed to double the pr...

1/2 mole of helium gas is contained in a container at S.T.P. The heat energy needed to double the pressure of the gas, keeping the volume constant (heat capacity of the gas = 3 Jg–1 K–1) is –

A

3276 J

B

1638 J

C

819 J

D

409.5 J

Answer

1638 J

Explanation

Solution

DQ = nCv DT, ms = 3JgKel\frac{3J}{g - Kel}, nCv = 3

14\frac{1}{4} × Cv = 3 \Cv =12JmolKel\frac{12J}{mol - Kel}, n¢Cv =12\frac{1}{2}×12 = 6

DQ = n¢ Cv DT = 6 × 273 = 1638 J