3.1: THERMOCHEMISTRY
Thermodynamics is the study of the relationship between heat and other forms of
energy, particularly mechanical work.
... [Show More] Thermochemistry is the part of thermodynamics
that deals with the quantity of heat given off or absorbed during a chemical reaction. The
quantity of heat given off or absorbed during a physical change or temperature change
can also be studied, and we will refer to this process as calorimetry.
In order to adequately discuss thermochemistry, we need to define some common terms.
System - the object (or substance) being studied
Open system - a system that permits the transfer of mass and energy with the
surroundings
Closed system - a system that permits the transfer of energy but not mass with the
surroundings
Isolated system - a system that does not permit the transfer of energy or mass with
the surroundings
Surroundings - the rest of the universe interacting with the system
Energy - the potential or capacity to move matter: the ability to do work (unit is J =
joule)
Work - the amount of energy transferred by a force acting through a distance
Kinetic energy - the energy possessed by an object by virtue of its motion (unit is J =
joule)
Potential energy - the energy possessed by an object by virtue of its position (unit is J
= joule)
Heat (q) - the thermal energy transferred between system and surroundings due to a
difference in temperature between them (unit is J = joule)
Enthalpy - the total energy of a system
Heat of reaction - (ΔH) the amount of heat (q) gained or lost during a chemical
reaction
Exothermic - a reaction with a - ΔH
Endothermic - a reaction with a + ΔH
You must be able to use the terms above to describe a thermochemical
system.
Calorimetry
The energy change that accompanies a physical, temperature, or chemical change is
determined by carrying out the process in a device known as a calorimeter. The
calorimeter is able to measure the amount of heat absorbed or evolved as a process
takes place. A Styrofoam coffee cup calorimeter can be used to measure an energy
change that takes place at constant pressure. An enclosed bomb calorimeter is used to
measure an energy change that takes place at constant volume with a change in
pressure.
We will use the term calorimetry to refer particularly to measuring energy changes that
accompany temperature and physical change (state change or phase change) processes.
Temperature change calorimetry measures the thermal energy change occurring as
a system at higher temperature transfers kinetic energy to a system at lower
temperature, which is reflect [Show Less]