[startea13]

 I feel like I am doing everything correct but I am getting these marked wrong.


The question is find the ΔHrxn of the following reaction:
for the reaction of an aqueous solution of calcium chloride with an aqueous sodium sulfate solution to create a precipitate of calcium sulfate
I used the formation of enthalpies CaCl2(-794.96) Na2SO4 (-1384.49) CaSO4 (-14.32.69) NaCl (-410.9)
I added the products CaSO4 and 2NaCl
 (-1432.69)+2(-410.9)=-2254.49
The reactants:
(-794.96)+(-1384.49)=-2179.45
Then I used the formula sum of products-sum of reactants to get +75.04

The second question is What is the ΔH° for the precipitation of 411 g of lead(II) sulfate from aqueous solutions of lead(II) chloride and sodium sulfate?
Using these enthalpies of formation
PbCl2:-918.4
Na2SO4:-1384.49
CaSO4:-1432.69
NaCl:-410.9
I calculated
-918.4+2(-410.9)=-1740.2
-359.2+(-1384.49)=-1743.69
Then, -1740.2-(-1743.69)=3.49
I used the molecular mass of PbSO4:303.264 to find the moles: (411/303.264)=1.35525mol PbSO4
I multiplied the moles by the total enthalpy of the rxn: 4.7298

[UG]

(-1432.69)+2(-410.9)=-2254.49
The reactants:
(-794.96)+(-1384.49)=-2179.45
Then I used the formula sum of products-sum of reactants to get +75.04

Just a slight error with the products and reactants. It should be equal to -2254.49-(-2179.45)

PbCl2:-918.4
Na2SO4:-1384.49
CaSO4:-1432.69
NaCl:-410.9
I calculated
-918.4+2(-410.9)=-1740.2
-359.2+(-1384.49)=-1743.69
Then, -1740.2-(-1743.69)=3.49

The numbers and formulae you have given do not seem to match. Can you write a balanced equation for this reaction?

[startea13]

PbCl2:-359.2
Na2SO4:-1384.49
PbSO4:-918.4
NaCl:-410.9
I calculated
-918.4+2(-410.9)=-1740.2
-359.2+(-1384.49)=-1743.69
Then, -1740.2-(-1743.69)=3.49

The numbers and formulae you have given do not seem to match. Can you write a balanced equation for this reaction?

Thanks for your response. I believe that the balanced equation is PbCl2 +Na2SO4--> PbSO4 +2NaCl

Oh I see I accidentally included the wrong entropy of formation for the first product when typing it here, however I did use the correct one for my original answer. I edited the numbers above to show that.

[UG]

I calculated
-918.4+2(-410.9)=-1740.2
-359.2+(-1384.49)=-1743.69
Then, -1740.2-(-1743.69)=3.49
I used the molecular mass of PbSO4:303.264 to find the moles: (411/303.264)=1.35525mol PbSO4
I multiplied the moles by the total enthalpy of the rxn: 4.7298

Your working seems fine, I don't know why it's marked wrong. Just don't forget units in your final answer