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Author Topic: help with general chemistry question: calculating heat energy  (Read 4387 times)

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szh122

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help with general chemistry question: calculating heat energy
« on: December 04, 2008, 09:41:43 AM »

i have no idea how to answer these two problems. i do not know where to start. can anyone please help?? THANKS!!

how much heat energy is required to convert 75g or ice at -25 degrees C to steam at 125 degrees C given the information:
heat of vaporization of water 100 degrees C= 2258 J/g
heat of fusion of water at 0 degrees C= 333.6  J/g
specific heat of water (solid) = 2.04 J/g K
specific heat of water (liquid) = 4.18 J/g K
specific heat of water (gas) = 2.00 J/g K

how much heat is released when 150g of aluminum are cooled from 4000K to 298K given the info:
bp of Aluminum 2520 degrees C
freezing point of aluminum 660 C
heat of vaporization of aluminum= 284 kJ/mole
heat of fusion of aluminum= 10.8 kJ/mole
specific heat of aluminum .903 J/gC
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ARGOS++

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Re: help with general chemistry question: calculating heat energy
« Reply #1 on: December 04, 2008, 10:27:53 AM »

Dear szh122;

To get the total required heat you have to sum all partial heats.
To get a “Picture” over the whole process start with a Diagram, with Heat vs. Temperature and name the different phases.
Then you will know how you must use the given parameters to go with "eis/water/steam" from -25°C to 125°C.

The second you can do analog.

If you have troubles describe us the phases in order of your diagram, to get help.
Good Luck!
                    ARGOS++
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Formulas, in its best sense,  ARE ONLY Recipes for “A Picture”,  —
     If you DON’T catch “The Picture”, you are lost, - for ever!      (A++)

There is ONLY one correct Formula for the “Hydrogen”:  —
     The Atom/Molecule, ITSSELF!                          (Dr. R. Mory  1968)

"Make it AS SIMPLE AS possible,  — BUT NEVER SIMPLER!"  (A. Einstein)

szh122

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Re: help with general chemistry question: calculating heat energy
« Reply #2 on: December 04, 2008, 10:58:46 AM »

Thanks for your help but I'm still kinda lost...just wanted to get an idea of what the formula or steps were to answer the question.
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ARGOS++

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Re: help with general chemistry question: calculating heat energy
« Reply #3 on: December 04, 2008, 11:12:49 AM »

Dear szh122;

If you would have done the diagram you would have found 5 phases with 5 corresponding heats, see list below.

Can you try as a first step for ice/water/steam to complete this list?:
       h1 =  heat 75g ice from -25°C to 75g ice of 0°C.
       h2 =  convert 75g ice from 0° C to …….
       h3 =  heat  75g …….
       h4 =  convert 75g ……
       h5 =  heat  75g ……
Then we can start the different calculations and sum.


Good Luck!
                    ARGOS++

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Formulas, in its best sense,  ARE ONLY Recipes for “A Picture”,  —
     If you DON’T catch “The Picture”, you are lost, - for ever!      (A++)

There is ONLY one correct Formula for the “Hydrogen”:  —
     The Atom/Molecule, ITSSELF!                          (Dr. R. Mory  1968)

"Make it AS SIMPLE AS possible,  — BUT NEVER SIMPLER!"  (A. Einstein)

szh122

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Re: help with general chemistry question: calculating heat energy
« Reply #4 on: December 04, 2008, 11:43:39 AM »

so to convert ice to water to steam, would you use the specific heat of each?
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ARGOS++

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Re: help with general chemistry question: calculating heat energy
« Reply #5 on: December 04, 2008, 11:53:53 AM »

Dear szh122;

If you would have completed the list you would know, that’s correct!

But you have to remember as Mr. Borek told, that you have to do your homework, we only help you to get it done.



Good Luck!
                    ARGOS++
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Formulas, in its best sense,  ARE ONLY Recipes for “A Picture”,  —
     If you DON’T catch “The Picture”, you are lost, - for ever!      (A++)

There is ONLY one correct Formula for the “Hydrogen”:  —
     The Atom/Molecule, ITSSELF!                          (Dr. R. Mory  1968)

"Make it AS SIMPLE AS possible,  — BUT NEVER SIMPLER!"  (A. Einstein)

szh122

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Re: help with general chemistry question: calculating heat energy
« Reply #6 on: December 04, 2008, 12:06:29 PM »

Thanks! Hopefully I can finish this. Really appreciate all your help.
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ARGOS++

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Re: help with general chemistry question: calculating heat energy
« Reply #7 on: December 04, 2008, 12:09:17 PM »

Dear szh122;

You’re welcome!   ─   Soon again.

Good Luck!
                    ARGOS++

P.S.:  If you like you can present your result to have it checked.
.
« Last Edit: December 04, 2008, 12:19:53 PM by ARGOS++ »
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Formulas, in its best sense,  ARE ONLY Recipes for “A Picture”,  —
     If you DON’T catch “The Picture”, you are lost, - for ever!      (A++)

There is ONLY one correct Formula for the “Hydrogen”:  —
     The Atom/Molecule, ITSSELF!                          (Dr. R. Mory  1968)

"Make it AS SIMPLE AS possible,  — BUT NEVER SIMPLER!"  (A. Einstein)

szh122

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Re: help with general chemistry question: calculating heat energy
« Reply #8 on: December 04, 2008, 07:25:27 PM »

thanks again. i figured it out. just took the mass x specific ht x delta temp for each stage. converted mass to moles and multiplied it by the heat of fusion and heat of vaporization and added the total. i'm pretty sure that's right.

is the second question the same concept??
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ARGOS++

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Re: help with general chemistry question: calculating heat energy
« Reply #9 on: December 04, 2008, 11:05:36 PM »

Dear szh122;

For water it sounds not bad, except that you have not to deal with moles at all, because all specific heat parameters are given per gram!

Of course that the second follows the same concept, but now you have to deal with both, some with moles and some with grams!

So take care for the units given!

Good Luck!
                    ARGOS++

Logged
Formulas, in its best sense,  ARE ONLY Recipes for “A Picture”,  —
     If you DON’T catch “The Picture”, you are lost, - for ever!      (A++)

There is ONLY one correct Formula for the “Hydrogen”:  —
     The Atom/Molecule, ITSSELF!                          (Dr. R. Mory  1968)

"Make it AS SIMPLE AS possible,  — BUT NEVER SIMPLER!"  (A. Einstein)
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