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Section 111.notebook February 28, 2012 Work can transfer energy to a substance which increases the internal energy of the substance. Internal energy can then decrease through the transfer of energy as heat. Energy can be transferred to a substance as heat and from the substance as work. Internal energy of a substance has been treated as a single quantity to which energy is added or taken away. Such a substance is a system. System a collection of matter within a clearly defined boundary across which no matter passes. All parts of a system are in thermal equilibrium with each other before and after a process adds or removes energy. 1 Section 111.notebook February 28, 2012 An example of a system would be a flask with water and a balloon on the end of the flask. The flask is heated and the temperature of the water increases. Eventually increasing the volume of the balloon. The system of the flask and balloon are treated as being isolated but most often are not. There is energy and heat transferred to the surroundings or enviroment. Enviroment everything outside a system that can affect or be affected by the system's behavior. 2 Section 111.notebook February 28, 2012 Work is the product of a force applied to an object and the distance moved by that object in the direction of the force. In thermodynamics work is the product of the change in the volume of a gas and the pressure applied on or by the gas. Defining Work in terms of Changing Volume W = Fd work = force x distance W = Fd(A) = (F) (Ad) = PΔV (A) (A) work = pressure x volume changes 3 Section 111.notebook February 28, 2012 If a gas expands ΔV is positive and the work done on the gas is positive. If a gas is compressed ΔV is negative and the work done by the gas is negative. When the volume remains constant there is no displacement and no work done on or by the system. An engine cylinder has a crosssectional area of 0.010 m2. How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5 x 105 Pa on the piston and moves the piston a distance of 0.040 m? 4 Section 111.notebook February 28, 2012 Three distinct quatities have been related to each other in thermodynamics 3. work (W) 2. heat (Q) 1. internal energy (U) not all three are involed in every thermodynamic process No work is done in a constant volume process Isovolumetric Process a thermodynamic process that takes place at constant volume so that no work is done on or by the system. Example: bomb calorimeter Isothermal Process a thermodynamic process that takes place at constant temperature and in which the internal energy of a system remains unchanged. 5 Section 111.notebook February 28, 2012 Adiabatic Process a thermodynamic process during which work is done on or by the system but no energy is transferred to or from the system as heat. Example: filling a balloon quickly 6 Section 111.notebook February 28, 2012 Practice 11A all Section Review all 7