Thermodynamics and Thermochemistry
10.0 Significance of $?H$ and $?E$
10.0 Significance of $?H$ and $?E$
(1) At constant pressure
$\Delta H = \Delta E + P\Delta V,$ ....(1)
According to the first law of thermodynamics
$$\Delta E = q + w$$
$$W = - P\Delta V$$
$$\Delta E = q - P\Delta V$$
from equation (1)
$$\Delta H = q - P\Delta V + P\Delta V$$
$$\Delta H = {q_p}$$
(2) At constant volume
$$\Delta E = q + W$$
$$\because W = - P\Delta V$$
$$\Delta E = q - P\Delta V$$
$$\Delta V = 0$$
