Chapter 9

# Chapter 9 - Chapter 9 Energy Enthalpy and Thermochemistry...

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Chapter 9: Energy Enthalpy, and Thermochemistry Study Guide Energy: the capacity to do work or to cause heat flow Law of conservation of energy: energy can be converted from one form to another but can be neither created nor destroyed The total energy content of the universe is constant Potential energy: energy resulting from position or composition Kinetic energy: energy due to motion of the object and depends on the mass of the object ( m ) and its velocity ( v ): KE = 1/2 mv 2 Heat: energy transferred between two objects caused by a temperature difference between them Heat involves a transfer of energy Work: a force acting over a distance Energy is a state function; work and heat are not State function: a property of the system that depends on its present state; a property that is independent of the pathway System: part of the universe on which we wish to focus attention Surroundings: everything in the universe surrounding a thermodynamic system Exothermic: refers to a reaction where energy (as heat) flows out of the system Endothermic: refers to a reaction where energy (as heat) flows into the system Thermodynamics: the study of energy and its interconversions Law of thermodynamics: the law of conservation of energy (energy can be converted from one form to another but can be neither created nor destroyed) Internal energy: sum of the kinetic and potential energies of all of the “particles” in a system; a property of a system that can be changed by a flow of work, heat, or both; ∆ E = q + w, where ∆ E is the change in the internal energy of the system, q is heat, and w is work E = q + w w = -P V w and P V have opposite signs since when the gas expands ( V is positive), work flows into the surroundings (w is negative)

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The work accompanying a change in volume of a gas is often called “PV work” The joule (J) is the fundamental SI Unit for energy: J = kg m 2 / s 2
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