Heat (q) is energy transferred between a system and its surroundings because of a temperature difference between them. It flows spontaneously from the hotter to the cooler region until their temperatures are equal. At constant pressure, the heat exchanged by a process equals its enthalpy change.

热(q)是因系统与环境之间存在温度差而在二者之间传递的能量。它自发地从较热区域流向较冷区域,直至二者温度相等。在恒压下,某过程交换的热量等于其焓变。