Yttrium2
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Potassium Chlorate vs Gummy bear
This is a cool reaction, -- Does this show how much energy is contained in sugar or just how much energy is released during the reaction of sugar and
the potassium chlorate?
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DraconicAcid
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It's the reaction between the potassium chlorate and the sugar. The reaction of sugar with oxygen will actually give off more energy, because the
conversion of potassium chlorate to KCl and oxygen is endothermic, IIRC. It just takes more time, so it's not as impressive.
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Yttrium2
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I think this is the part of chemistry that I missed out on, I am not sure what it is called-- What tells you that the reaction is endothermic / how
much heat or energy is produced? -- is it called heat of formation??
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j_sum1
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Yes, it is a fun classic.
The energy released in the reaction is from both reactants. But it does illustrate the amount of energy in sugars. You could compare other
substances and observe a far less energetic reaction.
That said, the drama of the reaction is a kinetic effect. This is not a slow release of energy as would be experienced through digestion of sugar.
This is all over pretty quickly.
One of the things I like about this reactionis the lilac colour of the potassium comes through in the flame.
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DraconicAcid
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Thermodynamics. You would use enthalpies of formation (heats of formation only if your textbook is from the 50s or so) to calculate it.
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Yttrium2
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Quote: Originally posted by DraconicAcid  | | Thermodynamics. You would use enthalpies of formation (heats of formation only if your textbook is from the 50s or so) to calculate it.
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I feel like a fool for not asking this, but an even bigger fool for not learning this.
Can you elaborate? Heat of formation is not an outdated concept ( I think), why would it be in books from only the 50's?
Can anyone explain in a bit of detail how to tell how much energy is released when certain bonds are formed? What is that called? -- Am I being a bit
unclear here?
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DraconicAcid
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It's not the concept that's outdated; it's the term. Heat is a form of energy transfer- heat can flow from one sample to another, or be given off,
but a substance does not "contain" heat. A sample will contain energy, which can leave the sample in either an organized fashion or a disorganized
one (or both). Organized energy flow is work; disorganized energy flow is heat. Heat and work are path functions, meaning that the amount of work and
heat you get from a particular process will depend on the conditions under which the process takes place.
Chemists often hate worrying about path functions- state functions (which depend only on the final state and initial state, not on how they got there)
are much more useful. One of these state functions is enthalpy (represented H, partially because E was already taken for energy, and partially
because they used to use the term heat interchangeably with it). You can calculate the deltaH for any reaction, based either on the products and
reactants enthalpies of formation, or by using bond enthalpies (counting up the bonds broken and the bonds formed, etc.). If you are working at
constant pressure, the change in enthalpy is equal to the heat absorbed by the reaction (which makes enthalpies easy to measure). If you're not
working at constant pressure, you'd get a different amount of heat given off or absorbed, but the enthalpy change would be the same.
Because enthalpy is a state function, you get the same deltaH for going from A to B, regardless of how you get there. The amount of heat given
off/absorbed will be different.
https://opentextbc.ca/chemistry/chapter/5-1-energy-basics/
[Edited on 22-6-2020 by DraconicAcid]
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Yttrium2
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I think it had something to do with enthalpy, I remember in chemistry class there was a list of values and I saw another students eyes light up when
he saw something on the list/table/chart. -- At the time I was a bit behind and had some difficulty understanding what was going on.
I believe the list was a list of enthalpy changes for various reactions going on. Any ideas as to what this list may have been?
On that website that DraconicAcid provided, under the Enthalpy section under Enthalpy of combustion it shows that there is far more energy released
during the combustion of isooctane (purportedly gasoline) then acetylene. -- This raises another question, in addition to my above question (which
hopefully will be answered) -- How come they cut the rail road tracks with oxy acetylene vs isooctane?
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DraconicAcid
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| Quote: | I think it had something to do with enthalpy, I remember in chemistry class there was a list of values and I saw another students eyes light up when
he saw something on the list/table/chart. -- At the time I was a bit behind and had some difficulty understanding what was going on.
I believe the list was a list of enthalpy changes for various reactions going on. Any ideas as to what this list may have been?
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Probably formation enthalpies. You can find the enthalpy change for any reaction by totaling the formation enthalpies of the products (each
multiplied by the coefficients from the balanced chemical eq'n) and subtracting the total formation enthalpies of the reactants.
| Quote: | | On that website that DraconicAcid provided, under the Enthalpy section under Enthalpy of combustion it shows that there is far more energy released
during the combustion of isooctane (purportedly gasoline) then acetylene. -- This raises another question, in addition to my above question (which
hopefully will be answered) -- How come they cut the rail road tracks with oxy acetylene vs isooctane? |
The enthalpies of combustion are per mole of fuel burned. Acetylene gives more heat per gram of fuel burned.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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