Heat and Work

Thermodynamics

  • Is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation.

  • HEAT CAN DO WORK


Heat Engines

  • Is a device that converts heat energy to work.

  • Takes many forms, from the internal combustion engine in cars to the giant turbines that generate electricity for houses.


Two Classification of Heat Engines

  • Internal Combustion Engines: Burns the fuel inside the engine

  • External Combustion Engines: Burns the fuel outside the engine


First Law of Thermodynamics

  • Is just another version of conservation of energy.

  • Simply states that part of heat transferred to an object is used by the object to do work.

  • The remaining heat changes the internal energy of the object.

Internal Energy: The sum of the potential energy in chemical bonds and the kinetic energy of the molecules.


Second Law of Thermodynamics

  • Limits the amount of work a heat engine can do for a certain amount of heat.

Three Versions of the Second Law of Thermodynamics

  1. Kelvin-Planck Statement: No heat engines can completely convert heat to work. In other words there are no 100 percent efficient heat engines. This statement limits the amount of work that a heat engine can do for a given amount of heat.

  2. Clausius Statement: Heat flows naturally from hot to cold objects.

  3. Entropy Statement: When a reversible process occurs, the total entropy of the universe remains the same. When an irreversible process occurs, the total entropy of the universe increases.

    Entropy - is a thermodynamic measure disorder.


Third Law of Thermodynamics

  • States that it is impossible to lower the temperature to 0 K (Kelvin) thus, even ideal efficiency cannot be 100 percent.

  • IDEAL Efficiency: is the efficiency of an ideal heat engine or a Csrnot Engine.