Estimate the Gibbs energy of formation of water at 350
Kelvin given the enthalpy and energy of formation at 298 Kelvin. Heat capacity data is missing.
Solution:
Both delta S and delta H are function of temperature. Delta G is given by delta H – T time delta S. In this case, delta H at 250 Kelvin is the
same as delta H at 298. Delta S at 298
can be calculated using delta G and delta H.
It is found to be minus 44.44 joules per mole per Kelvin. Now delta G at 350 Kelvin is calculated as
delta H minus T delta S. Its value is
minus 2.26 time 105 joules per mole.