Download Chapter 5 Thermochemistry Introduction/Definitions 5.1 The Nature

Chapter 5 Thermochemistry Introduction/Definitions
5.1 The Nature of Energy
 Thermodynamics is the study of energy and its transformations.
 Thermochemistry is the study of the relationships between
chemical reactions and energy changes involving heat.
Definitions:
 Energy is the capacity to do work or to transfer thermal energy
(heat).
 Work is energy used to cause an object with mass to move (ie.
Atoms, molecules, electrons, etc.)
 Heat is the thermal energy used to cause the temperature of an
object to increase.
 A force, F is any kind of push of pull exerted on an object (ie.
Atoms, molecules, electrons, etc.)
Kinetic and Potential Energies
 Kinetic Energy is the energy of motion: Ek = ½ m v2
 Potential Energy is the energy an object possesses by virtue of its
position or composition. (stored, potential to do “work”)
Examples: interaction between magnets, ball on top of a hill.
Energy Units:
 SI unit is the joule, J. 1 J = 1kg x m2/s2
Derived from on Ek = ½ mass (velocity)2,
So, kg(m/s)2 = kg (m2/s2)
 Traditionally, we use the calorie, cal as a unit of heat energy.
 1 cal = 4.184 J by definition. 1 calorie is the energy to heat 1
gram water, 1 oCelcius. (**We apply this definition when trapping
thermal energy “into” or “out of” a water sample. We call such
experimentation: “calorimetry”**)
 Nutritional Calories =
Cal = 1 kcal = 1000 calories = 4184 Joules = 4.184 kJ
Systems
 A system is the part of the universe we are focused on studying.
 Surroundings are the rest of the universe (i.e. the surroundings are
the portions of the universe that are not invoved in the system).
 Example: If we are interested in the interaction between hydrogen
and oxygen in a cylinder, then the H2 and O2 in the cylinder form a
system and the surroundings are the __________________.
 Transferring Energy: Work and Heat1
From physics (next year):
 Force is a push or pull on an object.
 Work is the energy used to move an object against a force.
W = F x d.
 Heat is the thermal energy transferred from a hotter object to a
colder one.
 Energy is the capacity to do work or to transfer thermal energy
(heat something).