Chemistry Exam 3 Chapters 6 7 8 Study Guide Chapter 6 Thermo Chemistry Key Equations U q w o First Law of Thermodynamics w P V Exothermic o Calculating work done by the system on its surroundings o Calculating work done on the system by its surroundings w P V Endothermic H U PV o Definition of Enthalpy H U P V o Calculating Enthalpy change for a constant pressure process Constant Pressure Processes Anything involving a Calorimeter or Calorimetry equations o Definition of heat capacity C ms q ms T q C T o Calculating heat change in terms of specific heat o Calculating heat change in terms of heat capacity H rxn n H f products m H f reactants o Calculating standard enthalpy of formation Hsolution U Hhydration o Lattice energy and hydration contributions to heat of solution Chapter 6 Key Terms Energy is the capacity to do work Types of Energy Kinetic Molecular motion Potential Energy available by virtue of an objects position Radiant Energy from the sun and earths primary energy source Thermal Energy associated with the random motion of atoms and molecules Heat Chemical Energy stored within the bonds of chemical substances Kinetic Molecular Theory of Gases Gases are composed of molecules whose size is negligible compared to the Attractive repulsive forces between two gas molecules are negligible distance between molecules EXCEPT when they collide Gas molecules move randomly in all directions and at various speeds When gas molecules collide the collisions are elastic the energy is conserved remains the same for the entire system The average kinetic energy KEavg of the molecules increases as the temperature increases KEavg mvavg and KEavg T 2 Therefore KEavg mvavg cT c some proportionality constant m mass 2 of molecule vavg average speed m s Increase Temperature increase the kinetic energy increase the of molecular collisions increase the Pressure Heat Transfer of thermal energy between 2 bodies that are at different temperatures Temperature is a measure of thermal energy Thermochemistry Study of heat exchange in chemical reactions Thermodynamics The scientific study of the interconversion of heat and other 1st Law of Thermodynamics Energy can be converted from one form to another kinds of energy but cannot be created or destroyed Diffusion When a gas mixes with another gas to occupy the space uniformly Effusion Process in which a gas flows through a small hole in a container Grahams Law of Effusion Under the same conditions of temperature and pressure rates of effusion are inversely proportional System Specific part of the universe that is of interest in the study Surroundings Everything else in the universe Different Systems Open System Can exchange mass and energy with is surroundings Ex Beaker with an open top Air surroundings can still exchange mass and energy with substance inside beaker Closed System Can exchange energy but not mass with surroundings Beaker with a closed top Can still exchange energy through its sides with energy that is outside Condensation of substance inside through temperature Freezing of substance inside through temperature Isolated System No exchange of Energy or Mass Example Sleeve for a closed beer keeps the insides from exchanging energy with the outside State Function A property of a system that refers only to its present state independent of path All that matters is where you start and where you end up Examples Volume Energy Pressure Temperature H Work is NOT a state function Since the energy in our universe is constant any change in our system any Because energy is not created or destroyed and energy lost by the system must be Exothermic Reaction Transfer of thermal energy from your system to your Heat absorbed from the surroundings by the system change in our surroundings 0 Usystem Usurroundings gained by its surroundings surroundings System gives off heat Heat x exothermic Hproducts Hreactants H 0 System doing work ON surroundings q P V Expanding gases Gas system is expanding in its container surroundings and therefore does work on its surrounds Compounds dissolving in excess acid Compound system is dissolving inside an acid surroundings meaning it is doing work on the acid Example When you go to the gym and are working out you system are doing work on the machines surroundings and are steadily losing energy Endothermic Reaction Transfer of thermal energy from your surroundings to your system Heat absorbed by the system from the surroundings System absorbs heat Heat x endothermic Hproducts Hreactants H 0 Surroundings doing work ON system q P V Piston compressing a gas The Piston surroundings is doing work on the gas system by compressing it Example When you have a birthday and alcohol surroundings is given to you system you become more and more happy as you become more drunk Enthalpy H is used to quantify the heat flow into or out of a system in a process H Heat given off or absorbed during a reaction at constant pressure that occurs at constant pressure H H products H reactants Enthalpy U q w heat work U Change in Internal Energy Ufinal Uinitial At constant pressure q H w P V U H P V H U P V Internal Energy U of a system is the sum of the kinetic molecular motion or potential energy which is the attractions repulsions between electrons and nuclei U The change in internal energy of a system Thermochemical Equations The physical states of all reactants and products must be specified in thermochemical equations H2O s H2O l H 44 0 kJ mol H2O l H2O g H 6 01 kJ mol A Comparison of H and U 2Na s 2H2O l 2NaOH aq H2 g H 367 5 kJ mol U H P V o At 25 C 1 mole H2 24 5 L at 1 atm P V 1 atm x 24 5 L 2 5 kJ U 367 5 kJ mol 2 5 kJ mol 370 0 kJ mol The specific heat s of a substance is the amount of heat q required to raise the temperature of one gram of the substance by one degree Celsius The heat capacity C of a substance is the amount of heat q required to raise the temperature of a given quantity m of the substance by one degree Celsius C m x s Heat q absorbed or released q m s t q C t t tfinal tinitial Constant Volume Calorimetry No heat enters or leaves qwater qbomb qrxn qsys 0 qsys qrxn qwater qbomb qwater m s t cbomb x t qbomb Reaction at Constant V H qrxn H qrxn Chapter 7 Key Equations u v o Planck s Quantum Theory o Used to calculate the speed of a wave by multiplying its wavelength and frequency o Relating energy of a quantum and of a photon to the frequency o Relating energy of a quantum and of a photon to the wavelength E hv o Planck s Quantum
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