Temperature Dependence of Enthalpy Quiz

1
Temperature Dependence of Enthalpy Quiz Use the
following data ?Hosublimation, 298.2 K
14.923 kcal Cp, I2 (s) 14.34 cal / (mol
K) Cp, I2 (g) 8.82 cal / (mol K) To
calculate the standard enthalpy of sublimation of
I2 at 500.0 K
500.0
K, 1.00 bar I2 (s) -----------------------------
gt I2 (g) DHosublimation, 500.0 K ?
2

• DHo1 500.0 K ? 298.2 KCp, I2 (s) dT
• (1.000 mol) (0.01434 cal / (mol K)) (298.2 K
  500.0 K)
• -2.894 kcal
• DHo2 14.923 kcal

• DHo3 298.2 K ? 500.0 K Cp, I2 (g) dT
• (1.000 mol) (0.00882 cal / (mol K)) (500.0
  K 298.2 K)
• 1.78 kcal
• DHosub, 500.0 K DHo1 DHo2 DHo1
• (-2.894 kcal) (14.923 kcal)
  (1.78 kcal)
• 13.81 kcal

3
Because I2 undergoes no phase changes between
298.2 K and 500.0 K, we can also write
DHsub, 500.0 K DHo1 DHsub, 298.2 K
DHo3 500.0 K ? 298.2 KCp, I2 (s) dT
DHsub, 298.2 K 298.2 K ? 500.0 KCp, I2 (g)
dT DHsub, 298.2 K 298.2 K ? 500.0 K (
Cp, I2 (g) - Cp, I2 (s) ) dT DHsub, 298.2
K 298.2 K ? 500.0 K DCp dT (1.000 mole)
( 14.923 kcal/mole) (0.01434 cal
/ (mol K) - 0.00882 cal / (mol K))
(500.0 K - 298.2 K) 13.81 kcal