Mixture of 50%Au-50% Cu (atomic percentage) forms a solid solution at high temperature, but a compound (CuAu) at low temperature.
(a) What is the free energy change when 1 mole of Cu and 1 mole of Au mix isothermally at 1150 K? Assume that Cu and Au form an ideal solution.
(b) Estimate the transition temperature between the AuCu compound and the Cu-Au ideal solution. The transition between the Cu-Au solution and the ordered compound is first order.
(c) The real transition temperature is 683 K. Explain the difference with your calculation. Specifically explain why you get a higher or lower transition temperature.
Data : Formation enthalpy for CuAu compound = -11904 J/mole
Formation entropy for CuAu compound = 0
Melting temperature for Cu = 1358 K
Melting temperature for Au = 1338 K
