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.

delta Hreaction = delta Hproducts - delta Hreactants

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?

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) = ??

drbob222 is correct . the answer is 200. DUh!!

It's -200. not 200

To calculate the standard enthalpy change (ΔH°) for the reaction at 25 degrees Celsius, you need to use Hess's Law and the standard enthalpies of formation for the reactants and products involved.

Hess's Law states that the total enthalpy change for a reaction is independent of the pathway taken as long as the initial and final conditions are the same. In this case, you can use the standard enthalpies of formation for each compound to calculate the ΔH°.

The formula to calculate ΔH° for the reaction is:

ΔH° = Σ(ΔH°f, products) - Σ(ΔH°f, reactants)

First, let's determine the enthalpy change of the reactants and products. We have:

Reactants:
O3(g): ΔH°f = 143 kJ/mol
NO(g): ΔH°f = 90 kJ/mol

Products:
O2(g): ΔH°f = ? (we need to look this up)
NO2(g): ΔH°f = 33 kJ/mol

Next, we need to find the standard enthalpy of formation (ΔH°f) for O2(g). You can find this value in a reference table or database. Once you have that value, we can substitute it into the equation to calculate ΔH°.

Now, let's substitute the values:

ΔH° = ΔH°f(O2) + ΔH°f(NO2) - ΔH°f(O3) - ΔH°f(NO)

Substituting the values we have:

ΔH° = ΔH°f(O2) + 33 kJ/mol - 143 kJ/mol - 90 kJ/mol

Simplifying the equation:

ΔH° = ΔH°f(O2) - 200 kJ/mol

Finally, the given table does not include the standard enthalpy of formation for O2(g). You will need to find this value in a reference table or database to substitute it into the equation.

By following these steps and finding the missing value, you can calculate the standard enthalpy change for the reaction at 25 degrees Celsius.