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8.63C

Posted: Sat Jan 09, 2016 9:35 pm
by 904475052_
Is there an error in the solutions for this problem because isn't the enthalpy of formation for K2S(aq) -471.5kJ/mol instead of -417.5kJ/mol?

Re: 8.63C

Posted: Sat Jan 09, 2016 9:55 pm
by Reine Nakamura 1C
Yes! I just did the calculations and got -38.72 kJ as the answer. When you use the 417.5 kJ/mol value, it makes the sum of the standard enthalpy of formation of all the products have a smaller negative value than that of the reactants. Therefore when you subtract the two negatives, it results in a + standard reaction enthalpy. However, when you use the correct 471.5 kJ/mole value, the sum of the standard enthalpy of formation for the products is a larger negative value than that of the reactants, resulting in a - standard reaction enthalpy (exothermic).