2.1 Physical Chemistry for Chemical Engineers

The concepts that form the basis of Physical Chemistry are important to chemical engineers, and flow into the more complex areas of Thermodynamics. This lesson will introduce some of the key concepts you will encounter in a Chemical Engineering Degree.

Enthalpy

A thermodynamic quantity, enthalpyA measure of the total heat content of a system. describes the total heat content of a system, related to the internal energyTotal kinetic and potential energy of all particles within a system., pressure, and volume. Enthalpy is most frequently discussed with regards to the enthalpy change of a reaction, where this can be a positive or negative value depending on whether the energy of the system increases (ExothermicA reaction that releases heat, where the products have less energy than the reactants. reaction) or decreases (EndothermicA reaction that ‘absorbs’ heat, where the products have greater energy than the reactants. reaction). This concept is visualised in Figure 1 below.

Enthalpy and Specific Heat Capacity can be related through the equations shown in Equation 2., where the relationship between heat capacity at a constant pressure can be related to a heat capacity at constant volume using the equation shown in Equation 3.