Thermochemistry deals with the heat changes that occur during chemical reactions. It is a branch of physical chemistry, along with thermodynamics which studies how energy transforms between different forms. Some key forms of energy include thermal, chemical, nuclear, and electrical energy. Energy cannot be created or destroyed, but instead transforms from one form to another according to the law of conservation of energy. A system is the specific part of interest being studied, and can exchange either mass and energy or just energy with its surroundings.

1. Thermochemistry
Thermochemistry  Branch of physical chemistry.
 Deals with thermal or heat change caused by chemical reactions.
Thermodynamics  Branch of physical chemistry.
 Deals with the study of energy and how it transforms.
 Definition of Energy:
The ability to do work.
 Forms of energy:
1) Thermal energy  Energy associated with random motion of atoms and molecules.
2) Chemical energy  Energy stored within the bonds of chemical substances.
3) Nuclear energy  Energy stored within collection of neutrons and protons in atom.
4) Electrical energy  Energy associated with the flow of electrons.
5) Potential energy  Energy available by virtue of an object's position.
 Energy transformations:
 Chemicals in food gives us mechanical energy.
 Sunlight provides light energy for the tree to make
its own food.
 Chemical gasoline provides energy for the motion
of the car.
 Electrical energy in the plug creates the heat to
run the stove.
 Law of conservation of energy 
Energy can neither be created nor destroyed; rather, it transforms from one form to another.
 System and surrounding
System  Definition of system
o Specific part of the universe that is of interest in the study.
 Types of system
Open Closed Isolated
Exchange Mass and Energy Energy Nothing
Shape
Surrounding  Definition of surrounding
o The part outside the system that exchange energy with the system.