17-04-2012, 11:29 AM
Internal Energy
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• The molecule as a whole can move in x, y and z directions with respective components of velocities and hence possesses kinetic energy.
• There can be rotation of molecule about its center of mass and than the kinetic energy associated with rotation is called rotational energy.
• In addition the bond length undergoes change and the energy associated with it is called vibrational energy.
• The electron move around the nucleus and they possess a certain energy that is called electron energy.
Work done when a volume is increased or decreased
Consider a gas in a container with a movable piston on top. If the gas expands, the piston moves out and work is done by the system on the surroundings.
Alternatively, if the gas inside contracts, the piston moves in and work is done by the surroundings on the system. Why would the gas inside contract or expand?
Heat
Heat like work, is a form of energy.
The energy transfer between a system and its surroundings is called heat if it occurs by virtue of the temperature difference across the boundary.
The two modes of energy transfer – work and heat- depend on the choice of the system.