[ryu1]

Hi

For this problem I add a picture from the book.

I basically multiplied the first reaction by 2 (multiplying the enthalpy by 2 giving 689.5*2 = 1379) and reveresed the order of the reaction (putting reactants as products and vice verse, changing the sign of the enthalpy to -1379.

then I added all the reactions together (the newly made first reaction along with the original 2 other reactions), adding up the enthalpy values, deleting common reactants that appear on both the reactants and the products sides, that gives us the wanted reaction and it's enthalpy.
(855.7-1001-1379=-1524.3)
the problem is, I got enthalpy -1524.3 and it's not in the choices.

Is there a problem in my calculation or in the choices?  (answer B has been corrected by our instructor after the workbook was printed to -1521.3 as I drawn in the picture, it doesn't mean it is the correct answer though).

Thank you for your help.

[Borek]

Perhaps instructor intended to changed the digit to 4, not to 1? It is rather clumsy written.

What you did looks OK to me.

[ryu1]

Perhaps instructor intended to changed the digit to 4, not to 1? It is rather clumsy written.

What you did looks OK to me.

I wrote that with the pen, they told us to fix it to 1521.3 by email (i just use white text in the picture as well to make it clearer as I see was right of me )

I asked her to check again if she REALLY meant to fix it to 1521.3 and not something else...
Thanks