The conservation of energy is a fundamental concept of physics along with the conservation of mass and the conservation of momentum. Within some problem domain, the amount of energy remains constant and energy is neither created nor destroyed. Energy can be converted from one form to another (potential energy can be converted to kinetic energy) but the total energy within the domain remains fixed.
Thermodynamics is a branch of physics which deals with the energy and work of a system. As mentioned on the gas properties slide, thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. In rocketry, we are most interested in thermodynamics in the study of propulsion systems and understanding high speed flows.
On some separate slides, we have discussed the state of a static gas, the properties which define the state, and the first law of thermodynamics as applied to any system, in general. On this slide we derive a useful form of the energy conservation equation for a gas beginning with the first law of thermodynamics. If we call the internal energy of a gas E, the work done by the gas W, and the heat transferred into the gas Q, then the first law of thermodynamics indicates that between state "1" and state "2":
E2 - E1 = Q - W
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Energy conservation
Subject: About conservation of energy... 
Wed Jun 08, 2011 1:48 am
