JEE MAIN - Physics (2019 - 12th April Morning Slot - No. 2)
Two moles of helium gas is mixed with three moles of hydrogen molecules (taken to be rigid). What is the
molar specific heat of mixture at constant volume ? (R = 8.3 J/mol K)
21.6 J/mol K
17.4 J/mol K
15.7 J/mol K
19.7 J/mol K
Explanation
$${f_{mix}} = {{{n_1}{f_1} + {n_2}{f_2}} \over {{n_1} + {n_2}}}$$
$$ \Rightarrow {{2 \times 3 + 3 \times 5} \over 5} = {{21} \over 5}$$
$${C_v} = {{fR} \over 5} = {{21} \over 5} \times {R \over 2} = 17.4$$ J/mol K
$$ \Rightarrow {{2 \times 3 + 3 \times 5} \over 5} = {{21} \over 5}$$
$${C_v} = {{fR} \over 5} = {{21} \over 5} \times {R \over 2} = 17.4$$ J/mol K
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