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understanding calculating reaction enthalpy

Posted: Thu Jan 31, 2019 1:16 pm
by josephyim1L
What does calculation of a reaction enthalpy refer to? Does it refer specifically to the heat of a reaction? I'm having trouble understanding this concept

Also, of the 3 methods Dr. lavelle described in class, which is the most-frequently used/"best method"?

Re: understanding calculating reaction enthalpy

Posted: Thu Jan 31, 2019 1:21 pm
by Kyither Min 2K
I would say yes that the enthalpy of a reaction refers to the heat of the reaction since all enthalpy of a reaction is, is the change in enthalpy or heat of a reaction and so that correlates to the heat given off/absorbed by the reaction. As for which of the 3 methods is best, it really depends on what you're given in the problem. If the problem gives you bond enthalpies, use bond enthalpies or Method 2. If the reaction gives you the standard enthalpy of a reaction, use method 3. If the reaction already gives you the heat of a reaction, use method 1 or Hess' law. HOWEVER, Lavelle did point out that method 2 or bond enthalpies aren't as accurate as the other 2 because it is based off of averages of bond enthalpies and not the exact bond enthalpies in the given equation.

Re: understanding calculating reaction enthalpy

Posted: Thu Jan 31, 2019 2:44 pm
by shaunajava2e
The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions.