Chem 1110 Chapter 9
Chem 1110 Chapter 9 Chem 1110
Popular in General Chemistry I
Popular in Chemistry
This 0 page Class Notes was uploaded by Samantha on Monday January 11, 2016. The Class Notes belongs to Chem 1110 at Auburn University taught by David M Stanbury in Winter 2016. Since its upload, it has received 11 views. For similar materials see General Chemistry I in Chemistry at Auburn University.
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Date Created: 01/11/16
Chem 1030 Chapter 9 Thermodynamics 1 The Nature of Energy a We will de ne energy as the capacity to do work or to produce heat b The law of conservation of energy states that energy can be conserved from one form to another but can be neither created nor destroyed i Energy is constant and total energy transferred will be constant ii There are two types 1 Potential Energy is energy due to position or composition 2 Kinetic Energy of an object is due to the motion of the object and depends on the mass of the object and its velocity The transfer of energy is called frictional heating It is important to recognize that heat and temperature are decidedly different i Temperature is a property that re ects the random motions of the particles in a particular substance ii Heat involves the transfer of energy between two objects due to a temperature difference 1 Work is de ned as a force acting over a distance 2 Thus there are to different types of energy transfer through heat or through work e Energy change is independent of pathway however work and heat are both dependent on the pathway f A state function refers to a property of the system that depends only on its physical state It does not depend in any way on the system s past or future g Chemical Energy i The system is the part of the universe on which we wish to focus attention the surroundings include everything else in the universe 1 In this case we de ne the system as the reactants and the products of the reaction ii When the reaction results in the evolution of heat it is said to be exothermic quotout ofquot that is when energy ows out of the system Reactions that absorb energy from the surroundings are said to be endothermic 1 The energy gained by the surroundingsystem must be equal to the energy lost by the systemsurrounding 2 In any exothermic reaction the potential energy stored in the chemical bonds is being converted to thermal energy random kinetic energy via heat an a The bonds in the products are stronger on average then those of the reactants in an exothermic reaction 3 In an endothermic reaction energy ows into the system as heat is used to increase the potential energy of the system a In this case the products have higher potential energy weaker bonds on average than the reactants iii The internal energy E of a system can be de ned most precisely as the sum of the kinetic and potential energies of all of the quotparticlequot in the system 1 E q w iv Thermodynamic quantities always consist of two parts a number and a sign 1 The number is the magnitude of the change 2 The sign is the direction of ow from the system39s points of view a Energy ows into a system endothermic q is positive b Energy ows out a system exothermic q is negaUve v The same conventions also apply to the ow of work 1 If the system does work on the surroundings energy ows out then w is negative 2 If the surroundings does work on the system energy ows in the w is positive 2 Enthalpy a Enthalpy H is a state function A change in enthalpy does not depend on the pathway between two states i E PV ii H q at constant pressure where only PV work is allowed 1 Exothermic H is negative 2 Endothermic H is positive 3 Calorimetry a Is the science of measuring heat is based on observing the temperature change when a body absorbs or discharges energy as heat b The heat capacity C is the heat absorbed divided by the increase in temperature i Speci c heat capacity the energy required to raise the temperature of 1 gram of a substance by 1 C ii Molar heat capacity the energy required to raise the temperature of 1 mole of a substance by 1 C 4 Hess s Law a In going from a particular set of reactants to a particular set of products the enthalpy change is the same whether the reaction takes place in one step or in series of steps in summary enthalpy is a state function b Characteristics of Enthalpy Changes i If a reaction is reversed the sign of H is also reversed ii The magnitude of H is directly proportional to the quantities of reactants and products in a reaction If the coef cients in a balanced reaction are multiplied by an integer then the value of H is multiplied by the same integer 5 Standard Enthalpies of Formation a Is de ned as the change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states b Standard states for a substance is a precisely de ned reference state c H Hproducts Hreactants d Elements are not included in the calculation since elements require no change in formation Chapter 12 Quantum Mechanics and Atomic Theory 1 Electromagnetic Radiation a Wavelength is the distance between two consecutive peaks or troughs in a wave b Frequency is the number of waves per second that pass a given point in space c C 299792458x10quot8 ms i Wavelengthxfrequencyc 2 The Nature of Matter a deltE nhv i nchange in moles ii h6626x10quot34 iii v frequency Epotonhcy KE 5mvquot2 hv1hv2 Emcquot2 Yhmv ER1n21n1 i R2178x10quot18 3 Quantum Numbers a N the size and energy of the orbital i SO 73919qu c Ml every number between I and l including zero