review exam 5

# review exam 5 - McCord THERMODYNAMICS (v1) Exam 4 Review...

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What sections? Chapter 9 sections 1-6 and Chapter 10 sections 1-9, 12-13. Plus Bond Energies (Chapter 13, Tables 13.6 and 13.7 - don’t memorize them but DO know how to use them to calculate ± H of a reaction). Thermo Speak As you venture through thermodynamics you will encounter the terms system, surroundings, and universe. You must have a good picture in your mind of what these are. The system is what is currently under study. It can be incredibly tiny (a living cell or even a molecule) or emmense (an eco-system or even star system). The surroundings are all the things that are wrapped around the system. Sometimes the border between the system and surroundings is obvious and well defined such as the stainless steel walls of the reaction chamber of a bomb calorimeter. Sometimes the surroundings are completely mixed homogeneously with the system which is the case in solution chemistry (the solvent surrounds each of the solute molecules which are completely dispersed into the solvent). Together, the system and the surroundings make up the universe . For our purposes, the universe is most likely the room we are doing the experiment in. The interaction between system and surroundings is really the immediate surroundings. We will generally define our systems via chemical reactions (or physical changes) shown as a balanced chemical equation. Such as the combustion of methane shown here CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l) reactants yields products before change after initial change final Below the reaction are three ways of describing the change (read left-to-right on each line). Realize here that when we start, only the methane and oxygen gas are our system. Anything that is not this methane and oxygen must be the surroundings. After the reaction our system is now the carbon dioxide and the water. We must quantify everything we can to get a complete description of this change. We need to measure state functions. State functions State functions are qualities or states of a system that are independent of the path by which the system arrived. Anything you can measure as matter “just sits there” is a state function. The main state functions that we constantly concern ourselves with are composition (formula), mass, volume, pressure, and temperature. We have very specific ways to measure each of these. Some ways are easier than others – temperature is easier than composition. In our study of thermodynamics we introduce four more state functions, all of which are pieces of the energy puzzle of matter. The four are internal energy ( E ), enthalpy ( H ), entropy ( S ), and free energy ( G ). Each of these energy based state functions will have a unique value for a given set of all the other state functions previously mentioned. What I mean is that if I know that I’ve got say exactly 30 grams of CaCO 3 at 25°C under 1 atm pressure then I also am aware of the fact that it also has an exact amount of internal energy, enthalpy, entropy, and free energy also. Do I know those values? Maybe, but usually not. For

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## This note was uploaded on 11/14/2011 for the course CH 53740 taught by Professor Mccord during the Spring '08 term at University of Texas.

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review exam 5 - McCord THERMODYNAMICS (v1) Exam 4 Review...

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