# Thread: Molar Heat of Combustion - just clarifying

1. ## Molar Heat of Combustion - just clarifying

Just wanted to make sure that I have cone this correctly:

Heated 0.142g of ethanol, temp increase = 10DC, mass of water = 100

Calculate heat of combustion per mole:

deltaH = -mCdeltaT
= -100 x 4.18 x 10
= -4180J
n(C2H5OH) = m/mm
= 0.142/12.01x2+1.008x6+16 = 71/23034
-4180/71/23034 = 1356.09kJ/g (exothermic)

Per gram:
-4180/0.142 = 29.44kJ/mol (exothermic)

..the second one seems wrong?

2. ## Re: Molar Heat of Combustion - just clarifying

i mean 1356.09kJ/mol
and 29.44kJ/g

3. ## Re: Molar Heat of Combustion - just clarifying

y not make it more simplier and just do, molar mass/ the mass u used
Then times that value by delta h to get molar heat of combustion?

4. ## Re: Molar Heat of Combustion - just clarifying

Isn't that what I did though?

5. ## Re: Molar Heat of Combustion - just clarifying

Nope u did, mass/ molar mass = moles
and then u did (energy vaule)/ moles, gives u the same answer, but i just find it a lot harder to follow LOL
But both will work, and the answer u provided is correct
enjoy

6. ## Re: Molar Heat of Combustion - just clarifying

yeah its DeltaMH = Q/n
Q = DeltaH
n=moles

well done.

7. ## Re: Molar Heat of Combustion - just clarifying

chemistry so easy

8. ## Re: Molar Heat of Combustion - just clarifying

thanks everyone

9. ## Re: Molar Heat of Combustion - just clarifying

Originally Posted by AbsoluteValue
chemistry so easy
*HSC Chemistry. =P

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