In this chapter we distinguished between thermodynamic functions such as energy, entropy and free energies which depend on the state of the system alone and quantities such as work and heat, which depend on the path between two states of a system. The first two laws of thermodynamics give us the state functions energy and entropy.
The absolute value of entropy is given by the third law of thermodynamics. Since the absolute values of energy, enthalpy and free energy cannot be ascertained, standard states at each temperature are defined as the states at a pressure of 1 bar for each substance. Estimation of U, H, A and G were shown through examples. The criteria for spontaneous changes were obtained in terms of U, H, A and G and the maximum work obtainable from a system at constant temperature was shown to be - A.
The maximum non pressure volume work such as nFwas shown to be equal to - G. Standard free energy changes were calculated for a few reactions. The dependence of free energy on pressure was estimated and the equilibrium constant was defined as the ratio of dimensionless pressures at equilibrium and this was related to the standard free energy change for the reaction.
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