<< Chapter < Page Chapter >> Page >

Thermochemistry

We will begin lab in the amphitheatre of DBH

Objective

  • To explore heat transfer through calorimetry.
  • To use calorimetry to determine the enthalpy of reaction of a strong acid and a strong base.
  • To use Hess's Law of Heat Summation to determine the heat of hydration in calcium chloride.
  • To explore a common use of heat of reaction in real life.

Grading

  • Pre-Lab (10%)
  • Lab Report Form (80%)
  • TA Points (10%)

Background information

When two objects at different temperatures are brought into physical contact, thermal energy will spontaneously transfer from the warmer object to the colder object until both objects have achieved the same temperature. Assuming the two objects are thermally insulated from their surroundings, the heat lost by the warm object is identical to the heat gained by the cold object. This is a manifestation of the Law of Conservation of Energy.

The heat transfer, q, is a function of the mass of the object (m), the change in temperature undergone by the object ( ΔT size 12{ΔT} {} ) and the object's specific heat ( C s size 12{C rSub { size 8{s} } } {} ). This statement can be expressed mathematically as

q = mC s ΔT size 12{ ital "mC" rSub { size 8{s} }ΔT} {}

Temperature change is always defined as T final size 12{T rSub { size 8{ ital "final"} } } {} - T initial size 12{T rSub { size 8{ ital "initial"} } } {} , which means that q for the hotter object ( q hot size 12{q rSub { size 8{ ital "hot"} } } {} ) is negative and q for the colder object ( q cold size 12{q rSub { size 8{ ital "cold"} } } {} ) is positive. If energy is conserved, then

q hot size 12{q rSub { size 8{ ital "hot"} } } {} + q cold size 12{q rSub { size 8{ ital "cold"} } } {} = 0

and

( mC s ΔT size 12{ ital "mC" rSub { size 8{s} }ΔT} {} ) hot size 12{ {} rSub { size 8{ ital "hot"} } } {} + ( mC s ΔT size 12{ ital "mC" rSub { size 8{s} }ΔT} {} ) cold size 12{ {} rSub { size 8{ ital "cold"} } } {} = 0

Now consider dropping an ice cube into water just warm enough to melt the ice cube but not warm enough to further heat the water from the cube. The observation is that the ice cube melts and the warm water cools to 0 ° size 12{0°} {} C. It is important to recognize that during the phase change, the temperature of the ice cube does not change. Therefore, it is not possible to use the preceding equation to determine the heat transferred. Rather, the energy transferred to the ice cube from the warm water affects the phase change. The energy equation is now adjusted to incorporate the enthalpy required to melt the ice cube, ΔH f size 12{ΔH rSub { size 8{f} } } {} (where f stands for fusion):

( mC s ΔT size 12{ ital "mC" rSub { size 8{s} }ΔT} {} ) warm size 12{ {} rSub { size 8{ ital "warm"} } } {} + ΔH f size 12{ΔH rSub { size 8{f} } } {} = 0

It is also possible to have thermal energy when chemical reactions occur. The amount and direction of heat flow is dependant on the chemicals reacting. Using a calorimeter, it is possible to experimentally determine the heat of reaction.

Calorimetry

In the technique known as constant-pressure calorimetry, enthalpies of phase changes or chemical reactions are determined indirectly by measuring temperature (at constant pressure) changes in a medium, most often water, surrounding the materials undergoing the change. That is, by measuring ΔT size 12{ΔT} {} of the water one can use the preceding equation to calculate ΔH size 12{ΔH} {} for the process of interest. Of course, this means one must know the mass of the water used and water's specific heat: C water size 12{C rSub { size 8{ ital "water"} } } {} = 4.18 J/(gK).

Today in Part I, you will add a strong base to a strong acid, measure the temperature change in the water as the two react, and use that information to calculate the heat of reaction per gram of NaOH. Then convert your experimental value into an enthalpy in kJ/mol (of NaOH).

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
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.
Bharti
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
Daniel
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
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
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
Abhijith Reply
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?
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
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
Good
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, Gen chem lab. OpenStax CNX. Oct 12, 2009 Download for free at http://cnx.org/content/col10452/1.51
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Gen chem lab' conversation and receive update notifications?

Ask