AP Chemistry 1.2 Laws of Thermodynamics
AP Chemistry 1.2 Laws of Thermodynamics. What is the standard enthalpy for the following reaction?
|AP Chemistry||Law of Thermodynamics|
Laws of Thermodynamics
The Laws of Thermodynamics
|Test Prep||AP Chemistry|
Here's the given reaction…lots of no's in there… [Chemical reaction equation]
And we're given the heats of formation for NO, N2O and NO2.
And here are our potential answers: This reaction is saying, “No, no, no!”
But we’re saying, “yes, yes, yes” to finding the standard enthalpy of the reaction.
Heh. Classic chemistry joke… Because nitric oxide is NO…? [Man thrown banana skins at him on stage]
Well we thought it was classic.
Anyway, to solve this problem, we need to find the standard enthalpy of reaction using
the following relationship: The enthalpy of reaction is equal to the sum
of the enthalpies of formation the products minus the sum of the enthalpies of formation [enthalpy of reaction definition]
of the reactants. Alright, well unlike staying awake after a
big lunch, this is actually pretty easy. In this reaction, our products are N2O and
NO2. We need to look at the heats of formation for these molecules given in the problem statement [Heat formation of N2O and NO2]
and add them up. Next, we see that the reactants are three
N O molecules, so we need to subtract three times the heat of formation of N O.
When we do the math, we find that the enthalpy of reaction is negative 154 kJ/mol, which
is answer (A). And yup, that's all she wrote. We're done.
Now that we’ve figured out this problem, it's time to reward ourselves with a big lunch…and [Boy eating food and falls asleep]
maybe a nap…