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Chapter_15_Notes

# Chapter_15_Notes - Chapter 15 Thermodynamics[15-1 The first...

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Chapter 15: Thermodynamics [15-1] The first law of thermodynamics Thermodynamics: is the study of energy changes that accompany physical and chemical processes- heat transfer o These changes usually involve heat (thus the “thermo” part of the term Energy is the capacity to do work or the capacity to transfer heat o Potential energy: is the energy possessed by virtue of position or composition o Kinetic energy: is the energy of motion o Either type can be measured in many forms HEAT is a common measure of heat Heat transfer occurs in two ways o Exothermic: release energy in the form of heat Heat is a product The potential energies of the products are lower than the potential energies of the reactants o Endothermic: absorb energy Heat is a reactant The potential energies of the products are greater than the potential energies of the reactants o Reactions (lots of rxns have activation energies, which just needs an activator. i.e. gasoline/wood and that spark) o chemical systems tend toward Minimal potential energy and Maximum disorder (entropy) o The First Law of Thermodynamics : The combined amount of matter and energy in the universe is constant. This is simply a re-statement of the Law of Conservation of Energy. Energy/matter is neither created nor destroyed in chemical reactions and physical changes. [15-2] Thermodynamics terms The system includes the substances involved in the chemical and physical changes being studied. o This is the stuff in the beaker! The surroundings include everything in the environment around the system. o Whatever is outside the beaker System + surroundings = universe The thermodynamic state of a system is the set of conditions that completely describes all of the properties of the system o The # of moles and identity of each substance o The physical state

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o Temperature o Pressure State Functions are properties of systems that are determined by specifying the condition or state of the system o Values of state function are independent on the history of this sample o Values depend only on the present condition of the system o Symbols for state functions are always capitalized (use this to clue you in when trying to figure out if something is a state function) State functions Non-state functions Temperature Work Pressure Energy(q) Volume Moles of substance Change in energy (∆E) Change in enthalpy (∆H) Entropy (S) The most important use of state functions in thermodynamic is to describe changes o Generally: ∆X= X(final) – X(initial) o This equation can be used to describe the difference in quantity o Depending on whether the value of the state function increases or decreases over time, X can be positive or negative Remember: q=mC∆T [15-3] Enthalpy Changes The quantity of heat transferred into or out of a system as it undergoes a chemical or physical change at con stant pressure qp is defined as the enthalpy change (∆H) for the process o H=qp o Exothermic: - H (negative) o Endothermic: +∆H (positive)
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