chemistry question?

Question

for ammonia, the enthalpy of fusion is 5.65 kJ/mol and an entropy of fusion is 28.9 J/K. mol. What is the melting point of ammonia? How do i start off?

Answer 1

You will need to use the equation for Gibb's Free Energy:

Delta(G) = enthalpy - T x entropy (T is the temperature in Kelvin)

When Gibb's free energy changes from being positive to negavite, the reaction becomes spontaneous, naturally going from reactants to products.

In this case, the fusion reaction is the change from solid to liquid. So, after G passes 0 (zero), the reaction will be spontaneous.

0 = 5650 - T * 28.9 (I converted the kJ into J to keep the units all the same)
28.9 T = 5650
T = 195.5 K
195.5 K = -77.5 °C = -171.5 °F