A volume of 100 ml of a liquid contained in an isolated container at a pressure of 1 bar. The pressu — Thermodynamics and Thermochemistry Chemistry Question
Question
A volume of 100 ml of a liquid contained in an isolated container at a pressure of 1 bar. The pressure is steeply increases to 100 bar by which the volume of liquid is decreased by 1 ml. The change in enthalpy, $\Delta H$, of the liquid is (Answer as ‘abcd’, where a = 1, if $\Delta H$ is +ve and a = 2, if $\Delta H$ is – ve, and ‘bcd’ is the magnitude of $\Delta H$, in J)
💡 Solution & Explanation
Isolated container ($q = 0$). Steep increase implies constant external pressure $P_2 = 100\text{ bar}$. $W = -P_2(V_2 - V_1) = -(100 \times 10^5)(-10^{-6}) = 10\text{ J}$. $\Delta U = q + W = 10\text{ J}$. $\Delta H = \Delta U + (P_2 V_2 - P_1 V_1) = 10 + (100 \times 10^5)(99 \times 10^{-6}) - (1 \times 10^5)(100 \times 10^{-6}) = 10 + 990 - 10 = 990\text{ J}$. Since it is positive, $a = 1$. Magnitude is 990, so 'abcd' = 1990.