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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.

Goals

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

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
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?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Mueller Reply
what is hormones?
Wellington
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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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