supplied to the system and the work 
done by the system will depend only on the initial and final equilibrium states and not on the process by which the change is brought about. [P7.3, P7.4, P7.5]
states: that if a system undergoes a change from one equilibrium state to another, the difference between the heat supplied to the system and the work done by the system will depend only on the initial and final equilibrium states and not on the process by which the change is brought about. [P7.3, P7.4, P7.5]
justifies: the introduction of a function of state known as the internal energy 
which changes by an amount
in the process. [P7.3, P7.4, P7.5]
represents: the conservation of energy, but also has an additional implication. Because and are not functions of state, their respective contributions to cannot be disentangled, and it does not generally make sense to speak of the 'heat content' of a system. [P7.3, P7.4, P7.5]
Copyright 1997, The Open University