4.9.2 Constant Pressure Heat Capacity

Since we've identified q with the enthalpy change in a constant pressure process, it is easy to see that

$$C_p = \left( \frac{dq}{dT} \right) _p = \left( \frac{dH}{dT} \right) _p$$ (4.9.47)

This is the molar heat capacity at constant pressure. It is the most commonly measured heat capacity. Often a single number is given for this heat capacity. Since C_p varies with temperature, this value is an average value valid at or near room temperature. For more accurate work tables are available giving the coefficients for the equation:

$$C_p = a + bT + \frac{c}{T^2}$$ (4.9.48)

or, less commonly in the form:

$$C_p = a + bT + cT^2$$ (4.9.49)

Of course, the values of a, b, and c are different in the two equations.