SUMMARY The goals of Chapter 17 have been to expand our understanding of energy and to develop the first law of thermodynamics as a general statement of energy conservation. General Principles First Law of Thermodynamics The first law is a general statement of energy conservation. Work W and heat Q depend on the process by which the system is changed. The change in the system depends only on the total energy exchanged not on the process. W 1 Q , D E th 5 W 1 Q Energy Thermal energy Microscopic energy of moving molecules and stretched molecular bonds. depends on the initial/final states but is independent of the process. Work W Energy transferred to the system by forces in a mechanical interaction. Heat Q Energy transferred to the system via atomic-level collisions when there is a temperature difference. A thermal interaction. D E th E th Important Concepts The work done on a gas is 52 (area under the pV curve) W 52 3 V f V i p dV The heat of transformation L is the energy needed to cause 1 kg
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