Heating Curves and Thermodynamics Heating curve of Water…

flinkexistenceMechanics

Oct 27, 2013 (3 years and 7 months ago)

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0


0

Melting /
Freezing


0

Melting /
Freezing


0

Melting /
Freezing

100


0

Melting /
Freezing

100

Boiling / Condensation


0

Melting /
Freezing

100

Boiling / Condensation




Thermodynamics: The study of energy (i.e.
what it is, how it is transformed from one form
to another, how it is used to get things done).


Š
As is probably obvious, this term is extremely
vague because it covers a huge number of
processes that take place in the world. To get
an understanding of what this really means, we
need to start where we usually do… at the
beginning.



Energy
:

The ability to do work or to produce heat. There
are two types of energy:




Kinetic energy:

The energy something has when it moves. (i.e.
moving objects, moving particles, vibrating molecules,
etc
)




Temperature

is a measure of the particles in an object. We
know this from the KMT, which says that the amount of energy is
proportional to the temperature (in K). The more the particles in
an object move around, the higher the temperature
.





Potential energy:
Stored energy that’s waiting for its chance to get
moving. (i.e. objects that are waiting to fall off of a shelf, energy
stored in chemical bonds,
etc
).




Chemical potential energy:
The energy that’s stored in chemical
bonds.





One of the main laws that describe how energy
behaves in the world is called the
law of conservation
of energy

(also known as the “first law of
thermodynamics”):




Energy is never created or destroyed


it can only be
converted between potential and kinetic energy.




This means that you can change kinetic energy to potential
(and vice
-
versa), but you can never make the amount of
energy go away
.




Examples:


You
can use the potential energy of the bonds in gasoline in your
car to make your car move
.



You can use the energy of moving turbines (kinetic) to charge a
battery (potential)


How energy moves from one place to another:




Heat (q):

The movement of energy from one thing to another
through the motion of molecules (thermal energy).




Heat spontaneously moves from hot things to cold. This is why a hot
pan can burn you and you can’t burn a hot pan


the energy goes
only from the pan to you because it’s hotter.




Heat and temperature are NOT the same thing
: Heat is the transfer
of energy, temperature is a measure of the kinetic energy of the
object once the energy has finished transferring.




Example: If I give you five dollars, the money is what I give you
(heat) and your net value is what goes up after you get the money
(temperature). Your wealth is not a five dollar bill, but the five
dollar bill does affect it.





Work
(w):
The movement of energy from
one thing to another through the motion of
larger things (mechanical energy).




When a weight is lifted up a hill, work has been
done on it (this is what you’ll learn in physics).




In
chemistry, heat is a lot more useful than work because chemistry
generally deals with the movement of atoms and molecules a lot more
often than it deals with the movement of large machines
.





Since heat (energy that’s being transferred through thermal motion)
is more important than work (for our purposes), how do we measure
it? More definitions of use:




System: Whatever we’re studying.




This can be practically anything. If we are studying what happens when we
heat a pan on the stove, the pan will be the system we are studying.




If a system gets energy added to it, the amount of energy it has after the
change is positive. Because of this, an
endothermic

process is any
process in which energy is absorbed by the system we’re talking about.




If a system has energy taken away from it, the amount of energy it has after
the change is negative. Because of this, an
exothermic


process
is any
process in which energy is given off by the system we’re talking
about
.





The

The amount of


energy in the

products is
greater


than the energy

in the reactants….


so this process is


ENDOTHERMIC.


This means the


reaction

ABSORBS energy


The


The

The amount of


energy in the

products is
less

than the energy

in the reactants….


so this process is


EXOTHERMIC.


This means the


reaction

GIVES OFF energy