9First Law of Thermodynamics: The internal energy of an isolated system is constant.
10The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings.
11Signs (+/-) will tell you if energy is entering or leaving a system. + indicates energy enters a system.- indicates energy leaves a system.
12First Law of Thermodynamics thermo: heat dynamics: force Work done on water by paddle-wheel is converted to thermal energy First Law: Heat added = Work done orHeat added = Thermal energy increase + = Work done by system
13Heat can be used to do work. Heat and work are energy transferred to or from a system.
14Work done on or by a gas is the pressure times the change in volume. W = PDV
15Work is the transfer of energy that takes place when an object is moved against an opposing force i.e. a system does work when it expands against an external pressureCar engine: petrol burns & produces gases which push out pistons in the engine and transfer energy to the wheels of carWork stimulates uniform motionHeat and work can be considered as energy in transit
16Ex: An engine cylinder compresses a volume of gas by 0. 04 m3 Ex: An engine cylinder compresses a volume of gas by 0.04 m3. How much work is done by the cylinder if it exerts a constant pressure of 7.5 x 105 Pa?
17G: P = 7.5 x 105 Pa, DV = 4 x 10-2 m3U: W = ?E: W = PDVS: W =(7.5 x 105)(4 x 10-2)S: W = 30,000 J
18DU = Q + WQ = quantity of heat that enters or leaves a system.
19DU = the change in internal energy. W = work done on (+) or by the system (-).
20Ex: When 5000 J of heat is added to an engine, the engine does 1250 J of work. What is the change in the internal energy of engine?
46Power plants and industrial factories are among the major contributors to the problem of thermal pollution. These facilities draw water from nearby lakes and streams, which they use to cool their machinery and steam-driven equipment. Although many such facilities now take care not to contaminate the water with chemical pollutants, few return the heated water to its original temperature before dumping it back into the lakes and streams from which it came. The heated water warms local bodies of water by as much as 10° C (18° F), making the water uninhabitable for fish and other organisms.
47Carnot EfficiencyThe maximum amount of energy that can be converted to work in a heat engine.