Thermodynamics
It is the study of heat changes. Increased temperature
increases molecular motion. Energy is the ability to do
work. Joules (J) and calories (cal) are the most common
energy units. Energy can be transferred through work
applying a force over a distance.
Energy changes of physical and chemical
processes
First law of thermodynamics states that energy can not be created or
destroyed in physical or chemical changes. Heat is the flow of
energy from higher temperature particles to lower temperature
particles.
Enthalpy, entropy and free energy
Enthalpy (H) takes into account the internal energy of the sample
along with pressure and volume. Under constant pressure, heat and
enthalpy are the same. Enthalpy of reaction is the net energy change
during a chemical reaction. In endothermic reaction, the system
takes in energy from the surroundings. ΔD is positive. In exothermic
reaction, the system gives off energy to the surroundings. Here, ΔH
is negative. Heat capacity is the amount of energy that can be
absorbed by a particle, before the temperature increases. When
changing between solids, liquids and gases, the temperature does not
change. Entropy is the randomness. Spontaneity occurs without
outside intervention. Second law of thermodynamics states that every
spontaneous process has an increase in entropy of the universe.
Determining spontaneity of a process
Spontaneity occurs without outside intervention. Temperature can
determine whether a process is spontaneous. Free energy (G) relates
temperature, enthalpy and entropy. Free energy is used to determine
if the reaction is spontaneous at a specific temperature.
Relating free energy and equilibrium
A chemical reaction that can proceed in both directions is called a
reversible reaction. A reaction is said to be at equilibrium when
the rate of the forward reaction equals the rate of the reverse
reaction. It takes time to establish equilibrium. The reactions
continue to proceed in both directions, but at the same rate is said
to be in dynamic equilibrium. At thermal equilibrium, two objects at
different temperatures, placed together will come to the same
temperature.
|
