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Thermodynamics (part 1)
Thermodynamics deals with energy
• Thermodynamics vs. Kinetics
e.g. energy of chemical reactions, energy of state changes
• Energy
Tells us what the equilibrium state of a system should be.
• Systems and surroundings
We can then infer possible directions to reach equilibrium.
• Phases
• Changes of state
Kinetics deals with rates and mechanisms
• Ideal gas law – an equation of state
Deals with specific pathways toward equilibrium.
• Temperature in Kelvins
Tells us if the equilibrium state is likely to be reached
• 0th law
under a given set of conditions.
• 1st law
Important because many systems do not reach equilibrium.
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System - Some portion of the universe that you wish to study
- Systems may be open or closed with respect to matter
Energy – the capability to do work
or energy
(ability to apply a force over a distance)
Surroundings - The adjacent
Examples:
part of the universe outside the
Potential energy – chemical, gravitational
system
Kinetic – velocity of an entire object
Thermal – internal kinetic energy
Changes in the system are
associated with transfer of
energy
Natural systems tend toward
(e.g. atomic vibrations, measured as temperature)
Electromagnetic – light, electricity
states of minimum energy
White Chapter 2
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Phase – a physically separable and largely homogeneous portion
of a system
Examples:
Liquid vs. solid H2O
Feldspar
Quartz in a granite
Gas bubbles in a magma
Quartz
one phase
two phases
two phases
Sample phase relations
http://serc.carleton.edu/files/research_education/equilibria/h20_phase_diagram.pdf
http://serc.carleton.edu/files/research_education/equilibria/alcohol-ice.pdf
http://serc.carleton.edu/images/research_education/equilibria/sio2.jpg
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Change of state – a change if the properties (e.g. energy) of a
system
Reaction – some change in the nature or types of phases in a
A state may be:
system
unchanging/static or transient/dynamic
A state that is static may be: metastable
or
equilibrium
An equilibrium state may be physical or chemical
reactions are written in the form: reactants = products
Energy barrier
Energy
e.g. A + B = C + D
In which state is a mixture
of H2 and O2 gas?
White Chapter 2
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Zeroth law of thermodynamics – thermal equilibrium
Equations of state – describe the relationship that exists among
the variables that describe the state of a system
There is no heat flow between objects that have the same
temperature (are in thermal equilibrium)
Example: the ideal gas law, PV = nRT
Scale of absolute temperature: Kelvins
P = pressure
V = volume
T = temperature
n = # of moles of gas
R = gas constant
0 K = -273.15 oC
At absolute zero, internal vibrations (thermal vibrations) cease
If one compresses a gas, what will happen?
If one heats a gas, what will happen?
Figure 5.5. Piston-and-cylinder apparatus to
compress a gas. Winter (2010) An Introduction to
Igneous and Metamorphic Petrology. Prentice Hall.
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First law of thermodynamics – conservation of energy
Also: equivalence between work and energy/heat
(e.g. compression of a gas in an adiabatic system)
energy neither created nor destroyed
path equivalence – all routes from A to B result in the same
net energy change
ΔU = Q – W
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Work and energy related to combustion within a cylinder
ΔU = Q – W
Change in internal energy = heat transferred – work
done
PΔV reflects work done by a gas
Work is force x distance
Consider what happens in a combustion engine
Bang!
Change in internal energy = heat transferred – work done
In the case of constant pressure, we can also define Enthalpy, ΔH
H = U + PV
Under constant pressure, ΔH = QP
ΔH values have been determined and tabulated for numerous chemical
reactions and phase changes (e.g. heat of reaction, heat of fusion, heat
of solution, etc.) and are used in many thermodynamic calculations
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