Thermochemistry ( Dr. Bülent BELİBAĞLI )

The part of the universe we choose to study is called a system. The parts of the universe with which the system interacts are called the surroundings. Three systems: open system, closed system and isolated system.

Internal Energy (E) is the total amount of energy (potential, kinetic, chemical energy,…) contained in a system. The components of internal energy are:

Translational kinetic energy

Molecular rotation.

Bond vibration.

Intermolecular attractions.

Chemical bonds.

Energy is the capacity to do work.

Work is done when a force acts through a distance. A system contains only internal energy.

– A system does not contain heat (q) or work (w).

– Energy transfer can occur as heat or work during a change in the system.

Chemical reactions may also do work.

• Gas formed pushes against the atmosphere.

• Volume changes.

• Pressure-volume work is done.

The most common type of work associated with chemical reactions is pressure-volume work. This is work involved in the expansion or compression of gases.

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