Question

The molar enthalpy of fusion (ΔH°) of ammonia is 5.650 kJ/mol, and the molar entropy of fusion (ΔS°) of ammonia is 28.900 J/mol K. Using this information, estimate the freezing point of ammonia. (You must answer in Kelvin.)

Answer 1

freezing implies liquid-solid co-existence, or the following equilbirium at constant temp:

ammonia (solid) <=> ammonia (liquid)

Let's say the solid ammonia and the liquid ammonia are both in standard states, whatever that means. at equilibrium, the gibbs free energy change is zero.

so delta G = standard delta G = ΔH° - TΔS° = 0

so T = delta H0 / delta S0

what's T? the freezing/melting point temperature in *Kelvin*!

Answer 2

i could plug in the numbers for you if you like

Answer 3

please

Answer 4

freezing point temp
= (5650 J per mol) / (28.900 J per mol per Kelvin)
= 195.5 Kelvin

we don't have to convert it to celsius in this case, but it's about -77 deg Celsius, and it sounds right. ammonia has a low freezing point.