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# deduce enthalpy change? watch

1. (Original post by PBC Gyal)
😂😂😂but why would you multiply?
the units are given as kj per mol... so if you multiply by mol you get kj....
2. (Original post by the bear)
the units are given as kj per mol... so if you multiply by mol you get kj....
Yeah exactly so kjmol-1 divided by mol gives you Kj....
3. (Original post by PBC Gyal)
Yeah exactly so kjmol-1 divided by mol gives you Kj....
ermmm no

kj/mol divided by mol is kj/mol2
4. (Original post by the bear)
ermmm no

kj/mol divided by mol is kj/mol2
Ohhhhh lol sorry I get it now, thank you very much 😜🙂
5. (Original post by PBC Gyal)
Ohhhhh lol sorry I get it now, thank you very much 😜🙂

6. (Original post by the bear)

Now my answer is 11757 KJ, doesn't that seem too much?
7. 1 mol of ethanol weighs 45 g.

so 394.5 g is 394.5/45 mol

multiply this by the enthalpy of combustion... you get 12019.1 kj
8. (Original post by the bear)
1 mol of ethanol weighs 45 g.

so 394.5 g is 394.5/45 mol

multiply this by the enthalpy of combustion... you get 12019.1 kj
Ahh okay thanks I hope that sticks in my brain 😂
9. (Original post by the bear)
1 mol of ethanol weighs 45 g.

so 394.5 g is 394.5/45 mol

multiply this by the enthalpy of combustion... you get 12019.1 kj
1 mol of ethanol weighs 46 g approx.
10. (Original post by the bear)
(Original post by charco)
1 mol of ethanol weighs 46 g approx.
Hi, would one of you mind helping me with an enthalpy question please?
It's based upon Hess's Law which I partially understand.
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11. (Original post by Matrix123)
Hi, would one of you mind helping me with an enthalpy question please?
It's based upon Hess's Law which I partially understand.
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If it's AS I can probably try
(was just doing some questions a few hours ago)
12. (Original post by surina16)
If it's AS I can probably try
(was just doing some questions a few hours ago)
Oh cool, thanks! It is AS
The question is based on a couple of previous questions:
Calculate the standard enthalpy change for the reaction between magnesium metal and silver nitrate solution. It gives steps to follow. First was to write out the equation and I got:
Mg (s) + 2AgNO3 (aq) ---> Mg(NO3)2 (aq) + 2Ag (s)
Then, it says to draw a Hess cycle which puts together this reaction and two previous ones which I worked out to be:
CuSO4 (aq) + Mg (s) ---> MgSO4 (aq) + Cu (s)
2AgNO3 (aq) + Cu (s) ---> Cu(NO3)2 (aq) + 2Ag (s)

My guess at a third part to the cycle would be:
Cu (s) + Mg (s) + NO3 (aq) + Ag (s)
^but that doesn't look right
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Updated: January 8, 2017
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