Download Themodynamic notes section 6.1

Chemical Thermodynamics
• The chemistry that deals with energy
exchange, entropy, and the spontaneity of a
chemical process.
Laws of Thermodynamics
• The energy in the universe is constant
• The entropy of a system not in thermal
equilibrium will increase.
• The entropy of a system approaches a
constant value as the system approaches
absolute zero.
Energy Exchange
Energy
• Measured in work and heat
• Can be changed into different forms
• Law of the conservation of energy
Heat vs. Temperature
• ∆T is an indication of particle movement
KE = ½ mv2
• Heat – energy change due to temperature
• The change in heat between the system
and the surroundings is what is measured
in thermodynamics.
Work and Heat
The energy of a system
• ∆ heat
• Work done by system or surrounding
First Law of Thermodynamics
• The change in the internal energy (DE) of a
thermodynamic system is equal to the amount
of heat energy (q) added to or lost by the
system plus work done (w) on or by the
system.
DE = q + w
• For work that only involves gas expansion or
compression, w = -pDV;
Values of Thermodynamic Functions
• FLoT: DE = q + w;
– q is assigned a positive value if heat is absorbed,
but a negative value if heat is lost by the system;
– w is assigned a positive value if work is done on,
but a negative value if work is done by the system.
– For processes that do not involve phase changes,
positive DE results in temperature increase.
More Values
Exothermic reactions
Energy loss = heat loss to surroundings
∆E < 0
or
∆E is (-)
Endothermic reactions
Energy gain = heat into the system
∆E > 0
or
∆E is (+)
Where is the energy
In a chemical reaction, energy comes from
the breaking and formation of the bonds.
Exothermic: energy from breaking bonds
(PE) produces thermal energy
Endothermic: the energy to make the
products is less than the reactions.
Requires thermal energy.
Practice problem 1
60 J of work is done on a gas and the gas
loses 150 J of heat to its surroundings.
What is the change in the internal energy?
What happens to the temperature of the
gas?
Practice Problem 2
How much work is required to compress a
gas from 7.3 L to 3.0 L by exerting a
constant pressure of 1.8 atm? Give your
answer in Joules and the correct significant
figures.
Explain your answer in reference to the
system and the surroundings.
Practice Problem 3
The internal energy of a gas increased 40 J
when 100 J of work was done by the gas on
a frictionless piston. Assume the gas is
ideal.
a) Was the volume of the gas increased or
decreased?
b) How much heat was transferred during
the process?
c) Was heat added or removed from the
system?