Heat of Transformation

A positive $\Delta H$ means that heat was absorbed during the transformation, as in the case of melting (positive means that you have to add heat to make it happen). Reactions that have a positive $\Delta H$ are called ``endothermic.''

Let's consider the reverse transformation liquid $\rightarrow$ solid (solidification).

$$\input{equations/93A}$$ (14-3)

Solidification is typically ``exothermic''--when something solidifies, heat is expelled (and has to be taken away as in the case of ice in the fridge).

Consider a plot the enthalpy as a function of $T$.

Figure 14-2: Enthalpy as a function of temperature at constant pressure.

Question: Where the ``zero'' is located on the ordinate axis.