Homework Help: Chemistry(Please help, thank you)

Posted by Hannah on Monday, February 13, 2012 at 9:31pm.

For the equation:

deltaHrxn = qrxn / mol substance to calculate deltaH per mole

what does the mol substance mean? Does this mean that you use the mm of the substance or if you already calculated the # of moles of a substance do you use that?

Chemistry(Please help, thank you) - DrBob222, Monday, February 13, 2012 at 9:49pm
It means you use the #moles of the substance you've already calculated.
Chemistry(Please help, thank you) - Hannah, Monday, February 13, 2012 at 9:49pm
ok thank you very much!!!
Chemistry(Please help, thank you) - Hannah, Monday, February 13, 2012 at 9:52pm
My qrxn value was 30267.23J and # of moles was 6.25e-3mol so that = 4842756.8 but are the units J/mol and do you think I should convert to kj?
Chemistry(Please help, thank you) - DrBob222, Monday, February 13, 2012 at 10:02pm
If you used specific heat as 4.184 J/g*C then the units you have are J/mol. Most tests quote kJ/mol for this type of work.
Chemistry(Please help, thank you) - Hannah, Monday, February 13, 2012 at 10:10pm
The units for the specific heat of water that they gave me were J/ g x K
Chemistry(Please help, thank you) - Hannah, Monday, February 13, 2012 at 10:12pm
So in that case I would just divide my answer of4842756.8 by 1000 = 4842.76 kJ/mol correct?
Chemistry(Please help, thank you) - DrBob222, Monday, February 13, 2012 at 10:16pm
yes.
Chemistry(Please help, thank you) - Hannah, Monday, February 13, 2012 at 11:14pm
I now need to find the enthalpies for Mg and MgO and then use the equations
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
MgO(s) + 2HCl(aq) ->MgCl2(aq) + H2O(l)
H2(g) + 1/2O2(l) delta H =-241.8 kJ

I do not understand how you find the values for the first two equations when there is only one value given.

Answer this Question

Related Questions

Chemistry - For the equation: deltaHrxn = qrxn / mol substance to calculate ...
Chemistry - Glycine,C2H502N, is important for biological energy.Find the heat of...
Chemistry - Calculate DeltaHrxn for the following reaction: C + H2O --> ...
Chemistry - Suppose 1.0 mol of substance A reacts with 1.0 mol of substance B. ...
Chemistry - If 0.120 moles of water are produced in the reaction H+(aq)+OH-(aq)=...
chemistry - calculate the enthalpy of formation, per mole, of sucrose, C12H2211O...
chemistry - calculate the enthalpy of formation, per mole, of sucrose, C12H2211O...
chemistry - C2H2(g) + 2 H2(g)--> C2H6(g) Substance So (J/mol∙K...
Chemistry - C2H2(g) + 2 H2(g)--> C2H6(g) Substance So (J/mol∙K...
Chemistry - C2H2(g) + 2 H2(g)--> C2H6(g) Substance So (J/mol∙K...

For Further Reading

First Name:
School Subject:
Answer: