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The foundation

We begin our study of the energetics of chemical reactions with our understanding of mass relationships,determined by the stoichiometry of balanced reactions and the relative atomic masses of the elements. We will assume a conceptualunderstanding of energy based on the physics of mechanics, and in particular, we will assume the law of conservation of energy. Indeveloping a molecular understanding of the reaction energetics, we will further assume our understanding of chemical bonding viavalence shell electron pair sharing and molecular orbital theory.


The heat released or consumed in a chemical reaction is typically amongst the most easily observed and mostreadily appreciated consequences of the reaction. Many chemical reactions are performed routinely specifically for the purpose ofutilizing the heat released by the reaction.

We are interested here in an understanding of the energetics of chemical reactions. Specifically, we wish to knowwhat factors determine whether heat is absorbed or released during a chemical reaction. With that knowledge, we seek to quantify andpredict the amount of heat anticipated in a chemical reaction. We expect to find that the quantity of heat absorbed or releasedduring a reaction is related to the bonding of the molecules involved in the reaction.

Prior to answering these questions, we must first answer a few questions regarding the nature of heat. Despiteour common familiarity with heat (particularly in Houston), the concept of heat is somewhat elusive to define. We recognize heat as"whatever it is that makes things hot," but this definition is too imprecise to permit measurement or any other conceptual progress.Exactly how do we define and measure heat?

Observation 1: measurement of heat by temperature

We can define in a variety of ways a temperature scale which permits quantitative measurement of "howhot" an object is. Such scales are typically based on the expansion and contraction of materials, particularly of liquid mercury, or onvariation of resistance in wires or thermocouples. Using such scales, we can easily show that heating an object causes itstemperature to rise.

It is important, however, to distinguish between heat and temperature. These two concepts are not one andthe same. To illustrate the difference, we begin by measuring the temperature rise produced by a given amount of heat, focusing onthe temperature rise in 1000g of water produced by burning 1.0g of methane gas. We discover by performing this experiment repeatedlythat the temperature of this quantity of water always rises by exactly 13.3°C. Therefore, the same quantity of heat mustalways be produced by reaction of this quantity of methane.

If we burn 1.0g of methane to heat 500g of water instead, we observe a temperature rise of 26.6°C. Ifwe burn 1.0g of methane to heat 1000g of iron, we observe a temperature rise of 123°C. Therefore, the temperature riseobserved is a function of the quantity of material heated as well as the nature of the material heated. Consequently, 13.3°Cis not an appropriate measure of this quantity of heat, since we cannot say that the burning of 1.0g of methane "produces13.3°C of heat." Such a statement is clearly revealed to be nonsense, so the concepts of temperature and heat must be keptdistinct.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
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.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket 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, General chemistry i. OpenStax CNX. Jul 18, 2007 Download for free at http://cnx.org/content/col10263/1.3
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