Single Choice

The average degrees of freedom per molecule for a gas are $$6$$. The gas performs $$25 \ J $$ of work when it expands at constant pressure. The heat absorbed by gas is

A$$75\ J$$
B$$100 \ J$$
Correct Answer
C$$150 \ J$$
D125 J

Solution

We know that, change in internal energy $$\Delta U=nC_v\Delta T=\dfrac{f}{2}\times nR\Delta T$$
Where, f=no.of degrees of freedom$$=6$$
Also, work done at constant pressure, $$\Delta W=nR\Delta T=25J$$

Heat absorbed=$$\Delta Q=\Delta U+\Delta W$$

$$=4nR\Delta T=4\times 25J$$

$$=100J$$

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