[Frederick95]

Why was my answer incorrect?




Question:
Try this question to see if you can use standard enthalpies to determine the molar enthalpy for the reactions given. Your answer must be in kiloJoules and accurate to 0 decimal places unless specified.

Find the molar enthalpy of a reaction with:
Solid calcium oxide and liquid water producing solid calcium hydroxide.Answer accurate to 1 decimal place


My answer:
CaO(s) + H2O(l) produces Ca(OH)2
38.1       69.95               83.4

69.95 (J /(mol x k)) / 1000 = 0.06995
38.1 (J /(mol x k)) / 1000 =0.0381
83.4 (J /(mol x k)) / 1000 = 0.0834

∆H = ∑n∆H°f(prod.) - ∑n∆H°f(react.)

     =.0834 - (.06995 + 0.0381)

     = .0834 - 0.10805

     = -0.02

     = -0.0 kJ /mol

[Borek]

Are you sure entalpies were not already in kJ?

[Frederick95]

Borek,

I used standard enthalpies  which were given in J /mol

[Borek]

Where did you get them from?

[Frederick95]

A chart entitled Molar Enthalpies and Enthalpies of formation(which doesnt want to send)

[Borek]

You either don't understand it or misread its content. Values you have listed have nothing to do with molar enthalpies of these subtances.

[Frederick95]

In that case, I will talk with my teacher about it

Borek, I was wondering if you can help both me and Marcus regarding his earlier question about PV =nRT (we are in the same class together). I am stuck on the exact last question he has asked.

May god Bless you