Transcript CHEM 112 General Chemistry 2

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Course Information
 Course Web Site
 Syllabus
 OWL
 Grading
 Lecture Schedule
 Laboratory
Thermodynamics
 “Thermodynamics is a funny subject. The first time
you go through it, you don't understand it at all. The
second time you go through it, you think you
understand it, except for one or two small points. The
third time you go through it, you know you don't
understand it, but by that time you are so used to it, it
doesn't bother you anymore.”
Arnold Sommerfeld, German theoretical physicist
What is Thermochemistry?
(aside from being loads of fun, of course!)
 Thermochemistry is the study of the relationship of
heat and chemical reactions
 Can tell us
 Whether a reaction will occur
 What drives a reaction
 In complex, systems, we can use thermochemistry in
combination with structural information to help
elucidate mechanisms
The wonderful things you can
do with Thermochemistry
or
How aminoglycoside
antibiotics kill bacteria
DNA

RNA
 (bacteria use different “machinery”)
Protein
 Studying small changes in the
heat absorbed or evolved by
the system can tell us how this
works
Aminoglycoside-rRNA Binding
Energy and Chemical Reactivity
Types of Energy
•
•
•
•
Kinetic
(motion)
Potential
(position)
Thermal
Mechanical
Electric
Sound
• Gravitational
• Electrostatic
• Chemical
The First Law of Thermodynamics
 Conservation of Energy= Energy is neither created nor
destroyed
 This means that Euniverse = 0
 During a chemical or physical change, energy will be
transformed from one type to another
Energy Interconversion
Wind moves
turbine
Turbine produces
electricity
Electricity is used
to lyse water into
H2 and O2
H2 is stored and
then burned
Energy Units
J
1J=
kJ
cal
kcal
BTU
0.2390 2.390 x 10-4
kWh
1
0.001
1 kJ =
1000
1
239.0
0.2390
1.0557 2.778 x 10-4
1 cal =
4.184 4.184 x 10-3
1
0.001
252 1.162 x 10-6
1 kcal =
4184
4.184
1000
1
0.252 1.162 x 10-3
1 kWh =
3.6 x 106
3.6 x 103
8.604 x 105
860.4
 Read as 1J = 0.2390 cal
1055 2.778 x 10-7
2.93 x 10-4
1
Temperature and Heat
 Heat (q) and Temperature (T) are not the same!
 The more thermal energy something has, the greater
the motion of its atoms
 The total thermal energy in an object is the sum of the
individual energies of all the atoms, molecules, or ions
What happens to thermal (heat) energy?
 Warms another object (transfer)
 Causes a change of state
 Is used in an endothermic reaction
Which statement below best describes the process of
placing a thermometer initially at 22ºC into ice water?
1.
Some of the thermal energy of the
ice water is transferred to the
thermometer.
2.
Some of the thermal energy of the
thermometer is transferred to the ice
water, melting some of the ice.
3.
The atoms of mercury begin to move
faster as a result of the thermal
energy transfer between the
thermometer and the ice water.
4.
The mercury in the thermometer
begins to expand as a result of the
thermal energy transferred.
25%
1
25%
25%
2
3
25%
4
Heat Transfer
 If heat (q) is transferred, in which direction does it go?
 From hotter to cooler (related to the 2nd Law, but we’ll
get to that later)
 Heat lost = Heat gained (1st Law)
qwarmer = -qcooler
 Thermal equilibrium= when two objects in contact
reach the same temperature
System and Surroundings
 System = The thing under study
 Surroundings = Everything else in the universe
 Energy transfer between system and surroundings
 Exothermic- system gives off heat
 Endothermic- system takes in heat
Heat Transfer
 When I heat an object, how much energy will it
require? It depends . . .
1. Quantity (How much stuff do I have?)
2. Size of the temperature change
3. Identity of the material
q

C

m


T