Posted by **Gemma** on Tuesday, February 8, 2011 at 12:05pm.

standard enthalpies of formation

H20(l) = -286 LiOH(s) = -487

standard enthalpies of solution for LiOH(s) to split into it's ions is 21

all values are in KJmol-1

Use the data given to calculate a value for the enthalpy change for the reaction of lithium with water.

I get how to do the cycle and I've seen the mark scheme and I don't understand why the 21 becomes negative.

I can draw my cycles. I use the equation in hess's law:

AH1 = AH2+AH3

= 286 - 487

= -201 and that is the wrong answer, it has -21 aswell so the answer is -222. I would have thought that if the solution was being formed then it would have a positive value as you are going in the right direction, is the mark scheme wrong or is there something I don't understand.

Thank you for any help you can provide.

## Answer this Question

## Related Questions

- Chemistry - Calculate the enthalpy change of formation for the following ...
- College Chem - Calculate the enthalpy of reaction from the standard enthalpies ...
- chemistry - Calculate the heat of formationof benzene if the heat of combustion ...
- Chemistry - What would you do in order to solve this question: "The enthalpy of ...
- chem - please help me? :) topic: standard enthalpies of formation "Calculate &#...
- chemistry - The standard enthalpy of combustion of C2H6O(l) is -1,367 kJ mol-1 ...
- chemistry - A scientist measures the standard enthalpy change for the following ...
- chemistry - A scientist measures the standard enthalpy change for the following ...
- chemistry - When NH3 is treated with oxygen gas, the products obtained are N2(g...
- Chemistry II - C4H4 (g) + 2 H2 (g) --> C4H8 (g) Combustion reactions involve ...

More Related Questions