Internal Energy and Enthalpy¶
The First Law¶
- Energy is always conserved, it cannot be created or destroyed (\(\Delta U=q+w\))
Definitions
Energy can only be transferred through two mechanisms:
- Work (\(w\)) - the transfer of energy as a result of unbalanced forces
- Heat (\(q\)) - transfer of energy resulting from a temperature difference
Adiabatic processes are those in which no heat, or mass is transferred between the system and its surroundings. Energy is only transferred through work
State Functions¶
Are properties that depend only upon the state of the system, and not the path used to get there.
While energy is a state function, work and heat are not, these are called path functions
- State functions can be integrated in the form \(\int_1^2dU=U_2-U_1=\Delta U\)
- Path functions are integrated in the form \(\int_1^2\delta w=w\) (not \(\Delta w\) or \(w_2-w_1\))
The sum of heat and work (inexact differentials) is an exact differential (\(\Delta U\))
At Constant Pressure¶
The equation can be rearranged to give \(q_P=\Delta U+P_{ext}\int_{V_1}^{V_2}dV\)
This means that \(q_P\) becomes a state function, called the enthalpy:
Info
At this point, the content came into the realm of stuff I’m already familiar with from Chemistry 2, so I copied the notes into this section, but won’t bother to add anything redundant.