• # question_answer 70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from $30{}^\circ C$ to $35{}^\circ C$. The amount of heat required (in calories) to raise the temperature of the same gas through the same range ($30{}^\circ C$ to $35{}^\circ C$) at constant volume is A)  30                 B)  50C)  70                 D)  90

Invoking first law of Thermodynamics for constant pressure process, we get $\Delta Q=\Delta U+\Delta W$ $70=\Delta U+nR\Delta T$ $70=\Delta U+2\times 2\times 5$ $\therefore$    $\Delta U=70-20=50\,$calories For constant volume process:$\Delta Q=\Delta U+\Delta W$ $\Delta U$will remain 50 calories because the temperature change is same and $\Delta W$will be 0 for constant volume process. $\therefore$$\Delta Q=50$calories Hence, the correction option is [b].