<< Chapter < Page Chapter >> Page >
C(s) + O 2 (g) → CO 2 (g)

produces 393.5 kJ 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 483.6 kJ for two moles of hydrogen gas burned, so q = -483.6 kJ. Therefore, more energy is available from the combustion of hydrogen fuel than from the combustion of carbon fuel. Because of this, we should not be surprised that conversion of the carbon fuel to hydrogen fuel requires the input of energy.

We can stare at the numbers for the heats of these reactions, 90.1 kJ, -393.5 kJ, -483.6 kJ, and notice a surprising fact. The first number 90.1 kJ, is exactly equal to the difference between the second number -393.5 kJ and the third number -483.6 kJ. In other words, the heat input in [link] is exactly equal to the difference between the heat evolved in the combustion of carbon ( [link] ) and the heat evolved in the combustion of hydrogen ( [link] ). This might seem like an odd coincidence, but the numbers from the data are too precisely equal for this to be a coincidence. Just as we do anytime we see a fascinating pattern in quantitative data, we should develop a model to understand this.

It is interesting that the energy of [link] is the difference between the energies in [link] and [link] , and not the sum. One way to view this is to remember that the energy of a reaction running in reverse must be the negative of the energy of the same reaction running forward. In other words, if we convert reactants to products with some change in energy, and then convert the products back to the reactants, the change in energy of the reverse process must be the negative of the change in energy in the forward process. If this were not true, we could carry out the reaction many times and generate energy, which would violate the Law of Conservation of Energy.

Let’s list all three reactions together, but in doing so, let’s reverse [link] :

C(s) + 2 H 2 O(g) → CO 2 (g) + 2 H 2 (g) q = 90.1kJ
C(s) + O 2 (g) → CO 2 (g) q = -393.5kJ
2 H 2 O(g) → 2 H 2 (g) + O 2 (g) q = 483.6kJ

What if we do both [link] and [link] at the same time?

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

Since O2 (g) is on both sides of this reaction, it is net neither a reactant nor product, so we could remove it without losing anything. [link] is then equivalent to [link] , except that we carried it out by doing two separate reactions. What if we do [link] in two steps, first doing [link] and then doing [link] ? That would be the same outcome as [link] so it must not matter whether we do [link] and [link] at the same time or one after the other. The reactants and products are the same either way.

What would be the energy of doing [link] and [link] either at the same time or in sequence? It must be the energy of [link] plus the energy of [link] , of course. So if we add these together using the above numbers, the energy of doing both reactions together is -393.5kJ + 483.6kJ = 90.1kJ. This is the energy of [link] and it is experimentally exactly the same as the energy of [link] .

This is a new observation. We have found that the energy of a single reaction ( [link] ) is equal to the sum of the energies of two reactions ( [link] and [link] ), which together give the same total reaction as the single reaction. When the separate reactions add up to an overall reaction, the energies of the separate reactions add up to the energy of the overall reaction.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
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.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Concept development studies in chemistry 2013' conversation and receive update notifications?