Homework Help: Chem

Posted by Dan on Monday, November 19, 2007 at 7:29pm.

Change in enthalpy problem. Consider the reaction represented below. Referring to the data in the table below, calculate the standard enthalpy change for the reaction at 25 degrees C.

O3(g)+NO(g)-->O2(g)+NO2(g)

Standard enthalpy of formation in kJ/mol:

O3(g) 143
NO(g) 90
NO2(g) 33

I am sure this isn't a hard problem, but I can't really remember how to do it.

Chem - DrBob222, Monday, November 19, 2007 at 7:39pm
delta H_reaction = delta H_products - delta H_reactants
- Chem - Dan, Monday, November 19, 2007 at 11:14pm
  Ok, so I have DeltaHrxn=(X+90)-(143+90). How do you calculate the enthalpy of O2 (X above) when it is not given to you. Am I even doing that right?
Chem - DrBob222, Tuesday, November 20, 2007 at 11:30pm
No. Re-read my answer. I said
PRODUCTS - REACTANTS.
You have one of the reactants on the product side.
DHrxn = DH products - DH reactants.
DHrxn = (O2 + NO2) - (O3 + NO)
DHrxn = (0 + 33) - (143 + 90) = ??
Chem - yea, Saturday, April 5, 2008 at 2:07pm
drbob222 is correct . the answer is 200. DUh!!
Chem - Nope, Thursday, January 8, 2009 at 8:52pm
It's -200. not 200
Chem - Nope, Thursday, January 8, 2009 at 8:53pm
It's -200. not 200

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