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by: Brady Spinka


Marketplace > University of Texas at Austin > Chemistry > CH 301 > PRINCIPLES OF CHEMISTRY I
Brady Spinka
GPA 3.98

Stacy Sparks

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Stacy Sparks
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This 17 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 301 at University of Texas at Austin taught by Stacy Sparks in Fall. Since its upload, it has received 22 views. For similar materials see /class/181859/ch-301-university-of-texas-at-austin in Chemistry at University of Texas at Austin.




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Date Created: 09/07/15
Chemistry Final Structure of Atoms o Rutherford s gold foil experiment Quantum Mechanics o Matter and energy are no longer separate entities o Matter including electrons behaves as both particles and waves 0 What is the frequency of orange light with a wavelength 600nm 0 Speed of light wavelengthfrequency 0 Frequency speed oflight wavelength Longer wavelengthlower frequency ROYGBIV shorter wavelengthhigher frequency Waves can interact o Constructive interference 9 waves in sync High and low points match up 0 Destructive interference 9 trough to peak The Nature of Matter 0 By the end of the 19th century it was widely accepted that matter and energy were different and distinct o Matter particles I Composed of mass I Position in space could be specified 0 Energy light energy made of waves I Contain no mass I Delocalized could not specify the position ofwaves in space 0 No intermingling of light and matter was assumed The photoelectric effect 0 Light metal electrons o The experiment 0 What can we vary I How much light I Wavelength of light I Type of metal I Angle o What can we measure I Energy of electrons I How many electrons 0 Results 0 Does the frequency oflight affect the number of electrons popped off the metal surface Intensity held constant I Frequency increasing I Wavelength decreasing 0 Does the frequency oflight affect the kinetic energy of the released electrons Intensity held constant I Energy goes up and up as we increase the frequency I Vo threshold frequency energy is 0 0 Does the intensity oflight affect the KE of electrons ejected from surface No 0 Does the intensity oflight affect the number of electrons ejected from surface Yes Increases with intensity 0 Einstein postulated 0 Light is made up ofparticles called photons I Think of photons as a packet of energy I Photons have no mass 0 Energy ofa phton is proportional to its frequency I Ehv E needed to overcome e attraction to metal 0 What does it all mean 0 KE hv hVo 0 Energy increases as frequency increases 0 Slope 6626 X 10quot34 Planck s constant h Thinking about the photoelectric effect with the idea that light has particlelike characteristics 0 Electrons are attracted to the metal nuclei 0 Remember there was a threshold frequency hVo below which no electrons are ejected o This amount of energy is known as a the work function for that metal 0 Photons with more E than a 0 Electron uses needed energy to escape pull of nucleus 0 Rest of energy shows up as the kinetic energy of the electron 0 From Einstein s graphs I KE e hv hvo Rethinking about the photoelectric effect results with our new understanding oflight o 1 electron can absorb 1 photon Either it has enough energy to eject electron or it doesn t o e doesn t increase If exactly at the threshold frequency you have enough energy to move it off but it could be recaptured Not enough energy to really go anywhere KE e increases with V o e increases with intensity 0 KE e stays constant with intensity Even though more e leaving surface KE does not change 0 Intensity of light is NOT related to the energyfrequency ofits photons Intensity is related to the number of photons o Ifyou increase frequency the same electrons would be ejected but they d have a higher KE Ifyou increase intensity more electrons would be ejected 0 Energy is quanitized because Ehv Gaps because there is a constant Can only have certain values Einstein s discovery also allowed us to quantitatively determine energy from frequencies or wavelengths o What is the energy in I of a single quanta of orange light wavelength 600nm o E hcwavelength 9 6626 X 10quot34 Is3 X 10quot8 ms 600 X 10quot9 m 3313 X 10quot19 I 0 Summary of conclusions 0 Energy is quantized E hv o Electromagnetic radiation appears t have particulate properties as well as wave properties dual nature of light Light as a wave phenomenon and as a stream ofphotons What is light 0 Is light a wave or particle 0 There is evidence for BOTH views oflight o This is called WAVE PARTICLE DUALITY o The defraction experiment supports the particle behavior of electromagnetic radation o The photoelectric experiment supports the wavelike behavior of electromagnetic radiation Louis de Broglie proposed that ALL MATTER has wavelike properties The Wave Nature of Matter 0 Wavelength h mv v velocity NOT frequency 0 1 1kgm2s2 o Diffraction patterns shine through regular crystal structures 0 Caused by waves being scattered by points spaced at similar distances to the wavelength of the wave If the wavelength is known the spacing can be found 0 ALSO observed with electrons neutrons etc o All matter eXhibits both particulate and wave properties 0 Large objects are mostly particulate the wavelength is too small to observe 0 Things that are extremely small photons energy light are mostly waves the particulate matter is relativistic it has no rest mass 0 Subatomic particles are both particulate and waves intermediate electrons protons neutrons Atomic spectrum ofhydrogen and wate we learned from it 0 White light has different wavelengths 0 Different elements have different spectrum Neils Bohr 0 Proposed 0 An atom s electrons eXist in discrete energy levels or quotorbitalsquot at fixed distance from the nucleus o Electrons may transition between transition between levels by absorbing or releasing energy I Absorb wavelength hop up energy level I Or quotrelaxquot into lower energy level I Different enerlgy levels the difference different wavelengths Extra energy being addedgt no overall change Only specific energy changes are observed 0 Electrons in hydrogen atoms must have only specific allowed energies because only specific changes in energy are observed 0 Bohr put together calculations to allow us to calculate the energies of specific levels and hence the energy changes 0 En 2178 X 10quot18 Ix ZZnz Terms 0 Continuous spectra shine white light through prism rainbow spectra 0 Emission spectra line spectra shining light emitted from certain element mostly black with few specific lines 0 Absorption spectra rainbow with black lines Shine white light but shine through tube of our sample opposite of emission o Quantized energy levels 0 Ground state Heisenberg s Uncertainty Principle 0 Macroscopic objects big particles 0 Waves 0 Now we consider a photon or electron 0 We CANNOT determine BOTH the POSITION AND the MOMENTUM possessed by a particle to extreme precision 0 As one becomes more accurate the other becomes less so If the position error is Ax and the momentum error is Ap then I Apr h411 o Ap mAv I heavier particle will have the greatest error but will have a smaller error in position 0 Review where we are up to now 0 Planck and Einstein established waveparticle duality via Ehv and explanation of the photoelectric effect From this also came quantization 0 De Broglie extends the idea ofwaveparticle duality to matter 0 Bohr extends quantization by applying it to the hydrogen atom o This explained spectra a known phenomenon 0 Didn t work for multielectron atoms 0 Heisenberg s Uncertainty Principle explains further complications about figuring out where the electrons are an atom The Schrodinger Equation 0 Hwave function Ewavefunction Wave function helps to describe an orbital The first three quantum numbers come from it Wave functionquot2 represents the probability offinding an electron in a given space probability density How likely we are to find an electron quotherequot or quotherequot Idea of where they re likely to be H has terms for different types of energy KE and PE Valid solutions are those which 0 Make sense mathematically don t become infinite 0 Have smooth variations in their value no instantaneousjumps from one region to the next 0 Only have one value at each point in space one y value for each value ofX Assume probability of finding an electron in the nucleus or at an infinite distance from the nuclears are both zero 0 Wave function2 0 no chance that the electron will be at that position Called node 0 Wave function 0 0 Has to be 0 at both boundary points to be a valid solution The Four Quantum Numbers 0 PRINCIPAL quantum number n o Describes main energy level and approximate nuclear distance 0 Shell 0 n any integer value starting at 1 o ANGULAR MOMENTUM quantum number L o Describes the shape in space occupied by the electorn o Sublevels or subshells o 0n1 o MAGNETIC quantum number mL 0 Describes the specific orbital within a subshell each of which have different spatial orientations o The number ofvalues of m1 gives you the number of orbitals for a given subshell o l0 o SPIN quantum number ms 0 Refers to the spin of an electron and the orientation of the magnetic field produced by this spin a simplistic model being the electron spins like a top 0 MS12 or12 PAULI EXCLUSION PRINCIPLE o No two electrons in the same atom may have the same four quantum numbers Electron Configurations o AUFBAU PRINCIPLE 0 Means quotbuilding up Start at lowest energy orbital fill it always obeing Pauli s exclusion principle and work up Would go against Aufbau principle to skip an orbital o HUND S RULE o For a set of degenerate orbitals the lowestenergy configuration of an atom has the maximum number of unpaired electrons Degenerate same energy 0 In other words electrons occupy degenerate orbitals singly before doubling up An electron in a 3s orbital will be closer on average to the nucleus than in any 3p orbital An electron in any 3d orbital spends even less time near the nucleus So the 3s orbital fills first then the 3p swhat s next 0 Paramagnetism and Diamagnetism o Atoms with unpaired electrons are called paramagnetic I These atoms are attracted to a magnet o Atoms with all paired electrons are called diamagnetic I These atoms are repelled by a magnet 0 Atomic Radii 0 We really don t measure the SIZE of these atoms We measure the distance BETWEEN two atoms and from that infer a radius 0 Cations are always SMALLER than their respective neutral atoms Anions are always LARGER than their respective neutral atoms 0 Increases from top to bottom Decreases from left to right Zea the pull of the nucleus on the valence electrons 0 An isoelectronic series consists ofions that have the same number of electrons Ions wants to be isoelectronic with noble gases 0 First Ionization Energy the minimum amount of energy required to remove the most loosely bound electron from an isolated gaseous atom to form a 1 ion As you move across a period ionization energy increases because Zeff is increasing Second Ionization Energy energy needed to remove an electron from a singly ionized ion an X ion More energy to pull off 2 101 electron more protons than electrons Electron Affinity o The CHANGE in energy when an electron is added to a gaseous atom to form a negatively charged ion Greater electron affinity most negative 0 EA values are generally negative indicating the process is exothermic energy is given off when the electron is added 0 If EA is large negative value this process is likely to occur 0 If EA is zero positive then this process is not likely to occur This is NOT the reverse process of first ionization energy 0 We start with a neutral atom and end with a 1 charged ion As you move down a group you would expect EA to become less negative Why 0 Less likely to add electron Because it has less attraction smaller Zea charge 0 From left ot right EA is more negative because Zeff gets larger 0 O Electronegativity 0 Measure of the relative tendency of an atom to attract electrons to itselfwhen Chemically combined with another element 0 Electronegativity is measured on the Pauling scale PERIODIC TRENDS SUMMARY 0 Periodic trends are due to trends in the electron configuration and effective nuclear charge Atomic radii ionic radii and electronegativity have fairly consistent trends IE and EA have trends with exceptions that are often predictable based on electron configuration although EA is less predictable overall 00 CHEMICAL BONDING Bonding results in a species that is more stable than the isolated atoms 0 Ionic bonding electrons are transferred metal ampnonmetal Due to some COULOMBIC ATTRACTION two charges separated by some distances Bigger fuller appart diminished attraction 0 Lewis dot formulas valence electrons I IfALL outer electrons are lost leaving the ion 39naked DO NOT show the neXt innermost level of electrons I Anions are shown with around them 0 Properties ofionic compounds stable I Lattice energy is the change in energy that occurs when the separated gaseous ions are packed together to form an ionic solid Come together to form crystal structure solid I LE kQ1Q2rl o R avg distance between cations and anions 0 K a constant for this crystal structure 0 Q charges on the ions 0 Lattice energy will be larger for large Q highly charged ions Lots of energies to overcome large lattice energy Electrons transferred from one element to another Forms lattice of anions negative ions and cations positive ions held together by a strong electrostatic attraction Compounds of Polyatomic Ions 0 Within the ions bonding between atoms is covalent but overall bonding between ions in the crystal is ionic Atoms become isoelectronic with closest noble gases by losing or gaining valence electrons Covalent bonding electrons are shared nonmetal atoms share valence electrons with other atoms to try to attain noble gas configurations We view sharing of electrons as sharing regions of electron desnity Electron density greatest between nuclei the covalent bond 0 Drawing dot structures 0 I How molecules share electrons Keeping track of the valence electrons I BONDING pair pair of electrons forming a covalent bond shown as a line between two atoms sometimes a pair ofdots is used I LONE or NONBONDING pair any pair of electrons notinvolved in bonding I Steps 0 Determine total valence e in molecule Write skeletal structure and start with single bonds between elements Fill in remaining electrons as lone pairs Try for OCTET around all except H and other exceptions Ifyou can t satisfy octet or exception rule for all atoms try double or triple bonds CHECK 0 Right number e around each atom o All available electrons assigned right total Essentially we are comparing 0 The number ofvalence electrons in the neutral free atom WITH the number ofvalence electrons quotbelongingquot to the atom in a molecule Assumptions 0 Lone pairs belong entirely to the atom o Bonding pairs are divided equally Most plausible formal charges are closest to zero May be an equally plausible structure if not most plausible one makes dominant contribution to any hybrid Sum of the PCs for all atoms overall charge zero for neutral molecule Hints o C almost always has 4 bonds and NO lone pairs 0 H always forms 1 bond 0 Halogens tend to form bond one Exceptions to octet rule 0 Be 4 e needed 0 B 6 e needed 0 Odd number of electrons in molecule 0 Expanded octets more than 8 e 0 Period 3 and higher may have but do not always have 0 Generally 10 or 12 electrons o VSEPR theory predicting molecule shapes Valence Shell Electron Pair Repulsion Theory Pairs of electrons around central atom arrange themselves as far apart in space as possible to minimize repulsion I Regions of High Electron Density RHED any area where valence electrons are found Each lone pair 1 region around CENTRAL atom Each bonded atom 1 region around CENTRAL atom Structure most stable when regions of HED are as far apart as possible I Two types of geometries 0 Electronic Geometry geometry of the molecule including both bonding pairs and nonbonding pairs Where the electrons are located arrangement of ALL areas of RHED around central atom 0 Molecular Geometry geometry that describes the locations of atoms in relation to each other quotshapequot describes locations of atoms but not lone pairs o MEMORIZE TABLE 0 Predicting molecule polarity I X and Y have identical electronegativies I X and Y have dissimilar electronegativities polar covalent 0 Electric dipole forms when a bond is polar covalent 0 Size depends on electronegativity difference bigger difference more polar larger dipole more ionic in character I X and Y have very different electronegativities ionic Molecular Orbital Theory 0 Atomic orbitals on different atoms combine to form molecular orbitals o Electrons in molecular orbitals belong to the molecule as a whole They are delocalized over the entire molecule 0 Molecular orbital theory is another bonding theory separate from the localized electron theory 0 MO theory allows more accurate prediction of 0 Magnetic properties 0 Bonding I Bonding orbitals stabilizing I Antibonding orbitals destabilizing No electron density between nuclei 0 Deciding which Mos to put the e in 0 Follow I Aufbau principle lowest E orbitals filled first I Pauli Exclusion Principle I Hund s rule will fill degenerate orbitals singly before pairing 0 Bond order bonding e antibonding e 2 I Greater bonder order we predict o More stable molecule 0 Shorter bond length 0 Greater bond E amount of E necessary to break a mole of bonds o Multiplestronger bonds have higher bond E 02 is more stable than 02391 Heteron uclear Diatomic Molecules 0 Combine the atomic orbitals unequally o AO s of different elements have samesimilar Aufbau order but have different energies due to difference in electronegativity quotNextdoor Heteronuclear diatomics o the differences can be assumed to be small enough that the same diagram as for a homonuclear diatomic can be used I eg we can use the N2 diagram for CN39 0 Other diatomics o If the difference is large enough some AO s do not mix These are called NONBONDING orbitals Delocalization in polyatomic molecules 0 Could combine all AO s for all valence electrons and then make that many MO s o Simpler method commonly used for molecules that exhibit resonance in their dot structures borrow from VB theory 0 Assume the sigma framework is just like VB theory overlaping 12 full orbitals The pi framework consists of Mos of the leftover p AO s O 0 Gas Laws 0 Gases molecules very far apart 0 Expands to fit available volume Creates a force on ALL sides of vessel described by a pressure measurement Compressible Volume amp pressure vary greatly with temperature Variables that in uence a gas sample I Temperature 0 0 C is where water freezes not absolute zero 27315K o 0 K absolute zero theoretical temperature at which molecular motion ceases and ideal gas volume tends to zero Charles s Law V1T1 VzTz V is directly proportional to the absolute T constant 11 P Average KE of gas particles is directly proportional to ABSOLUTE TEMPERATURE of the gas 0 Mean KE of C02 Mean KE of He 0 12 mCOZVZrmsCOZ 12 mHeVZrms He I Pressure force per unit area 0 Standard atmospheric pressure pressure exerted by Earth s atmosphere on a given day in a given location 0 760mmHg 760 torr 1 atm 101325 kPa 101325 bar 0 Boyle s Law P1V1P 2V2 Constant n T o Dalton s Law of Partial Pressures OOO o PaPmtal nanmtal or Pa Xa mole fraction Ptotal o Mole fraction ofmoles ofa total ofmoles I Volume 0 Avogadro s law V1n1V2n2 Constant T P Equal volumes of all gases at same T P contain the same number of molecules I Moles 0 One mole of any ideal gas occupies 224L at STP 0 Ideal Gas Law I PV nRT o R universal gas constant 00821 Loatmmolo K o LIQUIDS SOLIDS molecules close together 0 In water liquid is most dense ice oats in liquid less dense Kinetic Molecular Theory 0 For an ideal gas 0 Gases are very small discrete molecules spaced very far apart 0 The molecules are in constant random straightline motion until they hit another molecule or the vessel wall 0 Any collision is perfectly elastic no energy is lost or gained Between collisions molecules exert no attractive or repulsive forces on one another and they travel at cnstant speed individual molecules move at different speeds 0 Average KE of gas molecules increases absolute temperature increases with increasing temperatures Avg KE ofmolecules of different gases are equal at a given 0 o KE 12 mv2 loam 32 RT 0 Urms x3RTmolar mass in kgmol R 8314 kg m2s392 mol391 K391 O Diffusion and Effusion of Gases o Diffusion is the intermingling of gases 0 Effusion is the escape of gases through tiny holes 0 Graham s Laws 0 For two different gases at same T 39 R1R2 M2M1 o For samegas at two different temperatures 39 R1R2 T1T2 REAL GASES 0 Non ideal behavior in gases generally occurs at high pressures and low temperatures 0 High pressure I Gas compressed I Volume ofmolecules is significant fraction of container volume I Correction factor nb O o Nmoles o B dependent on SIZE ofmolecules I Vavailable Vmeasured nb Low temperatures I Molecules moving slowly I Attractive forces between molecules become important 0 Even more important at small V molecules closer together I Collisions with wall less often less energetic I Correction factor n2a V2 0 Van der Waals equation 0 P nZaV2V nb nRT LIQUIDS AND SOLIDS Types of forces 0 Intramolecular forces forces that hold together an individual molecule 0 Intermolecular forces forces between different molecules 0 O 0 Based on attraction of opposite charges electrostatic forces Based on molecular polarity A molecule which is polar overall with have a NET DIPOLE From now on we refer to this type of molecule as a DIPOLE Dipoledipole interactions I Forces between polar molecules dipoles I Positive end of one attracts negative end of the other dipoles lines up to maximize attraction minimize repulsion I Only about 1 the strength ofa covalent bond Hydrogen bonding I Subset of dipoledipole interactions I Molecules with H attached to O F or N I Highly polarized bonds London forces dispersion forces I Assumes existence of temporary instantaneous dipoles I TEMPORARY dipole induced as cloud gets distorted I Exact size and direction of temporary dipoles changes rapidly o Induces a complimetnary change in nearby molecules 0 They still continue to attract I Exist in ALL molecules but are the ONLY form ofinteraction in nonpolar molecules Stronger intermolecular interactions means it is harder to separate the component atomsions and means HIGHER melting and boiling points Properties of Liquids 0 Surface tension an inward force that prevents a liquid s surface area from expanding O Capillary action liquid creeps up sides of tube until limited by gravity concave if greater cohesive forcesconvex if greater adhesive forces 0 Cohesive forces hold liquid together 0 Adhesive forces hold liquid to another surface 0 Viscosity resistance to ow 0 quotFlowquot particles slide past each other Stronger attractive forces mean greater viscosity 0 As temperature increases get less viscous KE is higher to overcome atttraction easier to move past each other 0 EvaporationVaporization process by which molecules on the surface ofa liquid break away and go into the gas phase 0 Dynamic equilibrium rate of evaporation rate of condensation o Vapor pressure partial pressure of vapor molecules above the surface ofa liquid at a particular temperature 0 Water at 50 degrees would have higher vapor pressure than 25 degrees 0 Cal12 has higher vapor pressure than H20 at the same temperature Vapor pressure depends on temperature only Size of container and amount of liquid doesn t matter Aqueous solutions ofionic compounds 0 IonDipole interaction aqueous solutions ofionic compounds consist ofions surrounded by water molecules 0 HYDRATION water molecules surround ions 0 Electrolytes solutes that conduct electricity when in solution 0 Nonelectrolytes do not conduct Ionic Covalent Very Sometimes solvents solvents when molten when in aqueous often weaklypoorly solutions THERMODYNAMICS Nature of Energy 0 During any physical or chemical change energy changes in some way 0 First Law of Thermodynamics During any physical or chemical change the energy in the universe is conserved 0 Energy forms can be classified into categories 0 Total energy internal energy heat energy work energy Thermodynamic Terms 0 State functions o A property of the system whose value depends ONLY on the current state of the system NOT how it got to that state 0 Symbols are Capitalized o Enthalpy internal energy Gibbs free energy entropy temperature pressure volume 0 System the reaction reactants and products 0 Open exchange energy and matter 0 Closed exchange energy only 0 Isolated no exchange of energy or matter Surroundings the rest As big as it needs to be to account for ALL energy cahnges Universe Sys Surr Isothermal constant T Adiabatic constant heat q o Isobaric constant pressure Internal Energy E 0 Sum of the kinetic and potential energy of all particles in the system 0 AE q w Heat q o 1 cal 418411 Cal 1000 calories 1kcal 0 Signs 0 Endothermic o Exothermic 0 Phase changes 0 Meltingfreezing fusion 0 Boilingcondensation vaporization o Sublimination solid gas deposition gas solid 0 Adding in the numbers 0 Specific heat or Specific heat capacity Cs the amount of heat required to raise the temperature of 100 g ofa substance by 1 degree I Adding heat energy will cause a change in temp UNLESS o The heat is fueling a phase change 0 The heat is being used in a chemical change within the sample 0 Significant work is done on or by the sample 0 Heat ofVaporization AHvap heat needed to vaporize a specific amount of a SUbStance 39AHcondensation 0 Heat of Fusion heat needed to melt a specific amount of a substance Work w o w PextAV AnRT 0 Always consider the change from the system s point ofview 0 Positive w work done ON system BY surroundings an external force compresses a gas 0 Negative w work done BY system ON surroundings a gas expands pushing a piston outward o 1 atm 101325 Enthalpy H 0000 o H E PV 0 The enthalpy change AH is the quantity of heat transferred into or out ofa system as it undergoes a chemical or a physical change at constant pressure 0 AH greater than 0 endothermic 0 AH less than 0 exothermic Thermochemical equations and standard states 0 Rules 0 For a pure substance I The substance s most pure form when P 1 atm and T 298K I For liquids and solids the standard state is the pure liquid or solid I For a gas the standard state is the gas at 1 atm o For mixtures I For a solution the standard state refers to onemolar concentration of that substance I For a gas each entity must have a partial pressure of 1 atm o A thermochemical equation is a balanced chemical equation that includes its AH value 0 If the reaction is written with all the coefficients doubled change in enthalpy is also doubled Enthalpy of the reverse reaction has the same numerical value but opposite sign STANDARD ENTHALPY of reaction the AH value per mole of reaction when reactants in their standard states turn into products in their standard states Standard Molar enthalpies of combustion o AHmmbus 0 is for a combustion reaction usng 1 mol of the fuel 0 used to compare different fuels 0 unless specified assume possible products of combustion of any organic compound are nitrogen gas carbon dioxide gas and liquid water assuming the compound contains only C H N andor 0 OO O CALORIMETRY Bomb Calorimeter o constant volume W 0 0 AB qV Coffee Cup Calorimeter o constant pressure 0 heat evolved AH ifno change in volume 0 AE AH w if change in volume Calorimetry calculations 0 the calorimeter will contain a liquid 0 the system consists of the reaction in question The surroundings consist of the calorimeter and the liquid 0 Any heat released by a process occurring inside the calorimeter is absorbed by the calorimeter AND the liquid Hess s Law of Heat Summation the enthalpy change for a reaction is the same whether it cocurs by one step or by any series of steps 0 AH rxn AH products AH reactants Bond energy the amount of energy that must be absorbed to break a specific chemical bond Gas phases only The stronger a bond the higher its BE 0 AH rxn BE reactants BE products 0 Breaking bonds takes energy endothermic o Forming bonds releases energy exothermic 0 Net result of breaking and bond forming will give overall enthalpy of reaction SPONTANEITY ENTROPY AND FREE ENERGY Spontaneity o Spontaneous changes happen without any continuing outside in uences A spontaneous change has a natural direction A rxn or process is spontaneous if it can happen without external intervention 0 Ifwe set the process as the system then it is spontaneous ifit needs nothing from the surroundings o Spontaneity has nothing to do with the reaction rate 0 What drives a rxn or physical change to be spontaneous o Exothermic reactions are favored o More disorder is favored Entropy 0 Measure of disorder or randomness of the system 0 High disorder high S 0 Low disorder low S o Closely associated with the probability that the more ways a particular state can be achieved the greater the probability that that state will occur o 2 1 law in spontaneous changes the universe tends toward a state of greater disorder 0 Changes in entropy with temperature 0 The disorder ofa system is expected to increase when heat is added 0 Sign of AS depends on direction of heat ow 0 Magnitude of AS depends on temperature 0 Changes in entropy with volume or mixing 0 The disorder ofa system is expected to increase when a given amount of matter spreads into a greater volume or is mixed with another substance 0 AS qT energy must be transferred reversibly As T is higher change in entropy is lower for same amount of heat 0 When T is low change in entropy is high 0 3ml law the entropy ofa perfect crystal approaching 0 K approaches zero 0 The standard molar entropies increase as the complexity of a substance increases 0 AS rxn Sproducts S reactants o EXOTHERMIC v ENDOTHERMIC o Exothermic reactions I System gives out heat to surroundings I Often spontaneous even if gases convert to solids 0 Heat released must increase surrounding entropy enough to offset the loss of entropy in the system 0 How can an endothermic reaction be spontaneous I If reaction increases in entropy enough to offset the loss in entropy of the surroundings I The total energy in the universe must increase for ANY spontaneous process Gibbs Free Energy AG 0 AG AH TAS o the value of AG is an indicator of the spontaneity of a process I positive nonspontaneous I zero equilibrium Aern Aern TAern Free energy and equilibrium 0 a system at equilibrium does not change in either the forward or reverse direction


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