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Second, and perhaps more importantly for our purposes, we can use the known specific heat of water to measurethe heat released in any chemical reaction. To analyze a previous example, we observed that the combustion of 1.0g of methane gasreleased sufficient heat to increase the temperature of 1000g of water by 13.3°C. The heat capacity of 1000g of water must be 1000 g 4.184 J g ° C 4184 J ° C . Therefore, by , elevating the temperature of 1000g of water by 13.3°C must require 55,650 J 55.65 kJ of heat. Therefore, burning 1.0g of methane gas produces exactly 55.65kJ of heat.

The method of measuring reaction energies by capturing the heat evolved in a water bath and measuring thetemperature rise produced in that water bath is called calorimetry . This method is dependent on the equivalence of heat and work as transfers of energy, and on thelaw of conservation of energy. Following this procedure, we can straightforwardly measure the heat released or absorbed in anyeasily performed chemical reaction. For reactions which are difficult to initiate or which occur only under restrictedconditions or which are exceedingly slow, we will require alternative methods.

Observation 2: hess' law of reaction energies

Hydrogen gas, which is of potential interest nationally as a clean fuel, can be generated by the reaction ofcarbon (coal) and water:

C ( s ) + 2 H 2 O ( g ) C O 2 ( g ) + 2 H 2 ( g )

Calorimetry reveals that this reaction requires the input of 90.1kJ of heat for every mole of C ( s ) consumed. By convention, when heat is absorbed during a reaction, we consider the quantity of heat to be a positive number: inchemical terms, q 0 for an endothermic reaction. When heat is evolved, the reaction is exothermic and q 0 by convention.

It is interesting to ask where this input energy goes when the reaction occurs. One way to answer thisquestion is to consider the fact that the reaction converts one fuel, C ( s ) , into another, H 2 ( g ) . To compare the energy available in each fuel, we can measure theheat evolved in the combustion of each fuel with one mole of oxygen gas. We observe that

C ( s ) + O 2 ( g ) C O 2 ( g )

produces 393.5kJ for one mole of carbon burned; hence q -393.5 kJ . The reaction

2 H 2 ( g ) + O 2 ( g ) 2 H 2 O ( g )

produces 483.6kJ for two moles of hydrogen gas burned, so q -483.6 kJ . It is evident that more energy is available from combustion of thehydrogen fuel than from combustion of the carbon fuel, so it is not surprising that conversion of the carbon fuel to hydrogen fuelrequires the input of energy.

Of considerable importance is the observation that the heat input in , 90.1kJ, is exactly equal to the difference between the heat evolved, -393.5kJ, in the combustion of carbon and the heat evolved, -483.6kJ, in the combustion of hydrogen . This is not a coincidence: if we take the combustion of carbon and add to it the reverse of the combustion of hydrogen , we get C ( s ) + O 2 ( g ) C O 2 ( g ) 2 H 2 O ( g ) 2 H 2 ( g ) + O 2 ( g )

C ( s ) + O 2 ( g ) + 2 H 2 O ( g ) C O 2 ( g ) + 2 H 2 ( g ) + O 2 ( g )

Canceling the O 2 ( g ) from both sides, since it is net neither a reactant nor product, is equivalent to . Thus, taking the combustion of carbon and "subtracting" the combustion of hydrogen (or more accurately, adding the reverse of the combustion of hydrogen ) yields . And, the heat of the combustion of carbon minus the heat of the combustion of hydrogen equals the heat of .

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Concept development studies in chemistry. OpenStax CNX. Dec 06, 2007 Download for free at http://cnx.org/content/col10264/1.5
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