Transcript ChemLive Lesson 6.01 Thermochemistry Thermochemistry • Thermochemistry: study of the changes in energy that accompany chemical reactions and physical changes. • Thermochemistry is really all about.

ChemLive
Lesson 6.01
Thermochemistry
Thermochemistry
• Thermochemistry: study of the changes in
energy that accompany chemical reactions
and physical changes.
• Thermochemistry is really all about energy.
– Law of Conservation of Energy:
• Energy cannot be created or
destroyed, it can only be transformed from one form into another.
-Fuel is burnt to produce energy - combustion
(e.g. when fossil fuels are burnt)
-CH4(g) + 2O2(g) ----- > CO2(g) + 2H2O(l) +
energy
Thermal Energy
• What is it?
– Thermal Energy is the kind of energy that is
related to and/or caused by heat. When
thermal energy is applied to a substance, the
average velocity of the particles or molecules
which make up the substance increases -- and
it gets warmer!
– Example: Pot of boiling water on a fire.
Thermochemistry-Explained
There are two kinds of heat in chemistry.
1. The first is caused by physical activity. This extra
activity makes more molecular collisions occur. The
collisions create the heat (such as when you increase
the pressure in a system).
2. Chemical processes cause the second type of heat.
Instead of exciting a system and feeling the heat,
chemical bonds are made and broken, and the energy
is then released. A release of energy charges up the
system and the molecules bounce around faster,
resulting in that physical activity we just explained.
The opposite can also happen. Sometimes bonds are
made and broken and energy is absorbed. The area
then gets colder.
Heat- Explained
• Heat: The transfer of thermal energy from one
substance to another due to the temperature
difference between the two substances. It can be
described as the transfer of thermal energy from
one substance to another due to the temperature
difference between the two substances.
• A sample of matter can have a certain amount of
thermal energy, but the matter does not have
heat. Heat is the movement, or flow, of thermal
energy. Heat always flows spontaneously from
matter at a higher temperature to matter at a
lower temperature.
Heat- units of measurement
• Heat and thermal energy are both
measured in units of energy. The SI unit for
energy that is most often used by scientists
around the world is the joule (J).
• Another unit of energy that is commonly
used is the calorie, which is the amount of
energy it takes to increase the temperature
of one gram of water by one degree
Celsius.
Temperature
• Temperature is a measure of the average kinetic
energy of the particles in a sample of matter. The
greater the average kinetic energy of the particles
in a sample of matter, the higher the temperature
of that matter. To assign a numerical value to
temperature, scientists use defined temperature
scales (Fahrenheit, Celsius, and Kelvin).
Systems & Surroundings
• In thermodynamics, the world is divided
into a system and its surroundings
• A system is the part of the world we want
to study (e.g. a reaction mixture in a flask)
• The surroundings consist of everything
else outside the system
SYSTEM
OPEN
ISOLATED
CLOSED
Types of Systems
OPEN SYSTEM: can exchange both matter and
energy with the surroundings (e.g. open reaction
flask, rocket engine)
CLOSED SYSTEM: can exchange
only energy with the surroundings
(matter remains fixed) e.g. a sealed
reaction flask
ISOLATED SYSTEM: can exchange
neither energy nor matter with its
surroundings (e.g. a thermos flask)
• This lesson does not have an assignment
for you to turn in. However, before you go
on to the next lesson, make sure you are
able to compare and contrast temperature,
thermal energy, and heat, and that you can
differentiate between open, closed, and
isolated systems.