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### Topic: molar enthalpy of combustion of acetone next step?  (Read 34038 times)

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#### Frederick95

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##### molar enthalpy of combustion of acetone next step?
« on: March 07, 2008, 08:00:54 AM »
Calculate the molar enthalpy of combustion of acetone, using the experimental evidence.

Given:
Mass (m) of water: 100.0 g
Specific heat capacity(c) of aluminum: 0.91 J/ g degrees Celsius
Mass (m) of aluminum can: 50.0 g
Initial temperature (Ti) of calorimeter: 20.0 degrees Celsius
Final temperature(Tf) of calorimeter: 25.0 degrees Celsius
Mass (m) of acetone burned: 0.092 g

MY WORK IS AS FOLLOWS

Required:
Molar enthalpy of combustion of acetone?

Analysis
ΔT = tf - ti
= 25.0 oC - 20.0 oC
= 5.0 oC

Q = mc DT
= (100.0 g) (0.91 J/(goC)) (5.0 oC)
= 455 J
H = - Q = - 455 J = -0.455 kJ
Number of moles (n) = (given mass (g))/(gram-formula mass)
=

HOW DO I ACCOMPLISH THIS STEP?
THANKS AGAIN

#### Borek

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #1 on: March 07, 2008, 08:35:07 AM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

#### mo_1984

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #2 on: March 07, 2008, 03:29:23 PM »
i have the same rpoblem as fredrick listed. it is the EXACT same question he asked any1 plz help me how to do it.

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #3 on: March 07, 2008, 03:55:05 PM »

Dear Frederick95, Dear Mo_1984;

First Part:  ΔT is OK!

But Part 2:  Q = ….. is wrong!    It must be:  Q = QWater + QAl !!
(Remember: mWater is not equal mAl.)

Frederick95:  I think you know, since a short while, how to finish.

I hope it helps for both of you.

Good Luck!
ARGOS++

#### mo_1984

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #4 on: March 07, 2008, 04:14:43 PM »
yea but if u r putting in the mass of alu then u have to add the heat capacity also???

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #5 on: March 07, 2008, 04:20:02 PM »

Dear Mo_1984;

You’re right!, –   cAl for Al, and cWater  for …. !

Good Luck!
ARGOS++

#### mo_1984

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #6 on: March 07, 2008, 04:24:03 PM »
so when using q= mct formula for m add alu and water masses and for c add heat capacity for both???
and r u sure abt this man because every time i ask some1 they are telling me different answers so i am soo confused.

#### Frederick95

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #7 on: March 07, 2008, 04:42:18 PM »
Can you show us an example of this Argos?

Thank you for any further help

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #8 on: March 07, 2008, 04:42:43 PM »

Dear Mo_1984;

NO!,  –   I told you:  QTotal  = QWater + QAl !!
You need twice: Q = mcΔT !!!

Good Luck!
ARGOS++

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #9 on: March 07, 2008, 04:48:09 PM »
Dear Frederick95, Dear Mo_1984;

QTotal  = QWater + QAl   =  mWcWΔT + mAlcAlΔT.

I hope I have been of help to you.

Good Luck!
ARGOS++

#### Frederick95

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #10 on: March 07, 2008, 04:48:58 PM »
Thank you Argos:)

#### Frederick95

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #11 on: March 07, 2008, 04:57:11 PM »
Argos, do you have a link to any website that explains this formula?

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #12 on: March 07, 2008, 05:11:40 PM »

Dear Frederick95;

Not at the moment, -  but think about:

At begin both (Water and Calorimeter, build from Al) have the Temperature Ti.
After burning the Acetone both must have the identical Temperature Tf.
Conclusion:
Both must have taken enough Heat corresponding to their individual Mass m and individual  c!

That’s all.             You have to make you “A Picture” (see below).

Good Luck!
ARGOS++

#### ARGOS++

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #13 on: March 07, 2008, 05:21:31 PM »

Dear Frederick95, Dear Mo_1984;

Two (of a Lot) Links that may help a bit:
"Calorimetry”      "Calorimeter

Good Luck!
ARGOS++

#### Frederick95

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##### Re: molar enthalpy of combustion of acetone next step?
« Reply #14 on: March 07, 2008, 05:28:06 PM »
Argos -----Thanks

But.. My sum is 2317.5 kJ

I must find the molar enthalpy.

Is there a formula for this? I cannot find it:(