# 0.8 Energetics of chemical reactions  (Page 3/7)

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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 $1000g4.184\frac{J}{g°C}=4184\frac{J}{°C}$ . Therefore, by , elevating the temperature of 1000g of water by 13.3°C must require $55,650J=55.65\mathrm{kJ}$ 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:

$C\left(s\right)+2{H}_{2}O\left(g\right)\to C{O}_{2}\left(g\right)+2{H}_{2}\left(g\right)$

Calorimetry reveals that this reaction requires the input of 90.1kJ of heat for every mole of $C\left(s\right)$ 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, $C\left(s\right)$ , into another, ${H}_{2}\left(g\right)$ . 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

$C\left(s\right)+{O}_{2}\left(g\right)\to C{O}_{2}\left(g\right)$

produces 393.5kJ for one mole of carbon burned; hence $q=-393.5\mathrm{kJ}$ . The reaction

$2{H}_{2}\left(g\right)+{O}_{2}\left(g\right)\to 2{H}_{2}O\left(g\right)$

produces 483.6kJ for two moles of hydrogen gas burned, so $q=-483.6\mathrm{kJ}$ . 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 $C\left(s\right)+{O}_{2}\left(g\right)\to C{O}_{2}\left(g\right)$ $2{H}_{2}O\left(g\right)\to 2{H}_{2}\left(g\right)+{O}_{2}\left(g\right)$

$C\left(s\right)+{O}_{2}\left(g\right)+2{H}_{2}O\left(g\right)\to C{O}_{2}\left(g\right)+2{H}_{2}\left(g\right)+{O}_{2}\left(g\right)$

Canceling the ${O}_{2}\left(g\right)$ 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 .

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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 ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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