Practicing Success
Two moles of an ideal gas at 300 K were cooled at constant volume so that the pressure is reduced to half the initial value. Then as a result of heating at constant pressure, the gas expands till it attains the original temperature. Find the total heat absorbed by the gas, if R is the gas is constant : |
150R J 300R J 75R J 100R J |
300R J |
For 1 mol of gas : \(\Delta Q = C_V \Delta T + P\Delta T\) At constant volume : \(\Delta T = 0\) For 2 moles of gas : \(\Delta Q = 2C_V \Delta T\) From : PV = nRT = 2R x 300 and \(\frac{P}{2}V = 2RT_f\) \(\Rightarrow T_f = 150 \) K \(\Rightarrow \Delta Q = 2C_V (T_f - T_i)\) \(\Rightarrow \Delta Q = 2C_V (150-300)\) = -300 CV J In the next process : \(\Delta Q = 2C_P \Delta T = 2C_P (300 - 150)\0 \(\Delta Q = 300 C_P \) J Net heat absorbed = - 300 CV + 300 CP = 300 (CP - CV) = 300R J |