Question

Prove that Hess Law works. Show this by displaying which two thermochemical equations add up to the other. Also show how the corresponding two engergy values add up the other.

Answer 1

The equations are NaOH(s)->NaOH(aq)+42q/mol
NaOH(s) +HCl(aq)->H20+NaCl(aq)+91.1q/mol
NaOH(aq)+HCl(aq)->H2O + NaCl(aq) +.59q/mol

Answer 2

Chemistry question in math?

Answer 3

are you sure you have the right value for the enthalpy change in the third equation?

Answer 4

Yes.

Answer 5

can't be.

Answer 6

the source is probably wrong.

Answer 7

because?

Answer 8

the energy change in the second equation should be the sum of the energy changes in the first and third equations

Answer 9

The equations are NaOH(s)->NaOH(aq)+42q/mol
NaOH(s) +HCl(aq)->H20+NaCl(aq)+91.1q/mol
NaOH(aq)+HCl(aq)->H2O + NaCl(aq) +.59q/mol

add the first and third equations, then cancel the NaOH(aq) from both sides

Answer 10

you end up with 2 copies of the second equation with different energy outputs
and that shouldn't happen

Answer 11

oh.. Ok. this is starting to make some sense now. I didnt know how to find the equations to add. It does say in the next question why are they not exactly the same as the Hess Law suggest.

Answer 12

it definitely shouldn't be THAT far off.

Answer 13

I got the entropies off a lab. So too many variables that could have happened.

Answer 14

where are you that you use q/mol? all the labs I've seen used kJ

Answer 15

California. Oh yah. Im looking at it right now. it should be kj/mol.

Answer 16

Also if I had used half the grams of NaOH would it affect the heat absorbed by water?

Answer 17

so then say experimental error for what makes it not exact.

Answer 18

if you used half the amount of NaOH you would produce about half the heat?

Answer 19

and your uncertainty would be higher if you have to worry about that

Answer 20

Sorry I dont understand what you just said

Answer 21

then you don't have to worry about it :)

Answer 22

So it wouldnt matter about the grams?

Answer 23

@Peter14

Answer 24

no, if you halved the grams the reaction would produce half the energy so the water would absorb half the energy.

Answer 25

thanks. My chem teacher loves giving us labs that she never taught about. @Peter14

Answer 26

good luck