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Chemistry and the material world
123.102
Unit 4, Lecture 1
Matthias Lein
Magdeburg hemispheres (1650)
Otto von Guericke
1602 – 1686
Germany
Boyle's law: pV = const.
p1V1 = p2V2
Joseph Louis Guy-Lussac
1778 – 1850, France
Guy-Lussac's law: p/T = const.
Robert Boyle
1627 – 1691, England
p1T2 = p2T1
Charles' law: V/T = const.
V1T2 = V2T1
Jaques Charles
1746 – 1823, France
Robert Hooke
1635 – 1703, England
Avogadro's law: V/n = const.
V1/n1 = V2/n2
Amedeo Avogadro
1776 – 1856, Italy
ideal gas law:
pV = nRT
p is the absolute pressure of the gas
V is the volume of the gas
n is the number of moles of the gas
R is the universal gas constant
T is the absolute temperature
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Chemical thermodynamics allows us
to predict both the direction and the
extent of spontaneous chemical and
physical change under particular
conditions using a property called the
Gibbs free energy, G.
Josiah Gibbs
1839 – 1903, United States
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Chemical reactions and physical
changes almost always either absorb
or release energy as heat.
Energy may be distributed throughout
a chemical system in a large number
of different ways, some of which have
significantly higher probabilities than
others
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G = H – TS
H enthalpy of the system
–
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S entropy of the system
–
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Function related to the heat absorbed or
evolved by a chemical system
Measure of number of ways energy is
distributed throughout a chemical
system
T temperature in kelvin
ΔG = ΔH – TΔS
• ΔG allows us to determine whether a
particular chemical reaction or physical
change is spontaneous
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If ΔG < 0, the process is spontaneous
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If ΔG > 0, the process is
nonspontaneous
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If ΔG = 0, the system is at equilibrium
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System refers to the particular
chemical species being studied
Surroundings are everything else
• Universe refers to the system and the
surroundings
• Boundary defined as region across
which heat flows
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Open systems
–
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Closed systems
–
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Can gain or lose mass and energy
across their boundaries
Can absorb or release energy, but not
mass, across the boundary
Isolated systems
–
Can not exchange matter or energy with
their surroundings
Example: Open System
Example: Closed System
Example: Isolated System
(important: truly isolated systems do not exist)
Today we covered:
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Introduction into correlations between pressure, volume,
temperature and the number of moles for gases.
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Construction of the ideal gas law from these correlations.
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Description of all systems with the Gibbs free energy.
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Connection of spontaneous processes to the change in
the Gibbs free energy.
ΔG < 0
ΔG > 0
ΔG = 0
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spontaneous
non-spontaneous
equilibrium
Definition of a system, including the boundary and the
surrounding.
Open systems, closed systems, isolated systems