DOC PREVIEW
UNT CHEM 1415 - Exam 3 Study Guide
Type Study Guide
Pages 7

This preview shows page 1-2 out of 7 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 7 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

CHEM 1415 1nd EditionExam # 3 Study Guide Lectures: 16 - 22Lecture 16 (October 16)Introduction to Energy Energyo Potential Energy Associated with the relative position of an object The higher an object, the more potential energy it contains due to gravity Attraction and repulsion between electrical charges also leads to potential energyo Kinetic Energy Energy associated with motion When an object is falling, it is converting potential energy to kinetic energyKE=12m v2o Internal Energy Combined kinetic and potential energies of the atoms and molecules that make up an objecto Chemical energy Excess energy released if a chemical in bond breaking does not absorb all of the energy Type of potential energyo More specific forms of energy Radiant energy – associated with light or electromagnetic radiation Mechanical energy – movement of macroscopic objects Thermal energy – temperature of an object  Electrical energy – moving charges Nuclear energy – released in nuclear fusion and fission processeso Units SI unit – joule(J), 1 J = 1kg m2s2 Heat and Worko Heat Flow of energy between two objects, from the warmer one to the cooler one because of difference in temperatures, process not quantityo Work Transfer of energy accomplished by a force moving a mass in a distance Conservation of Energyo System – part of the universe that is being studiedo Surroundings – remainder of the universeo Boundary – separates the system and the surroundingsoE=q+wo∆ E=Efinal−Einitialo 1st Law of Thermodynamics Energy can be transformed between forms but cannot be created or destroyed Heat Capacity and Calorimetryo Calorimetry A set of techniques that observes heat flow into or out of a systemo Specific heat capacity, c Measures how much heat is required to raise the temperature of one gram of that material by 1℃q=mc ∆ To Heat of formation – the heat change for the production of one mole of a compound from its elements in their standard states Enthalpyo Heat flow under constant pressure conditions, Ho H = E + PVo Exothermic – heat evolves from a system, reaction can be used as a heat source, burning wood, hand warmers are a few examples, ΔH is less than zeroo Endothermic – heat is absorbed by the system, ΔH is greater than zeroo Amount of heat produced = n∗∆ Hphase changeLecture 17 (October 21)Hess’s Law; Heats of Reactions Hess’ Lawo Enthalpy change for any process is independent of the particular way the processis carried out. o State function – variable whose value depends only on the state of the system and not on its historyo∆ Hdesired=∆ HAi+∆ HAfo∆ Hdesired=∆ HBi+∆ HBf Specific Heat o The amount of heat required to raise 1 g of material 1 ℃oc=qm ∆ T∧q=mc ∆ TLecture 18 (October 23)Entropy; Second and Third laws of Thermodynamics Spontaneous Processo Takes place without continuous interventiono May occur quickly or over a long period of time Entropyo Does not depend on a function’s historyo Entropy of 1 mole of gas is usually much greater than one mole of liquid or solido Heating a system increases its entropyo Statistical mechanics – or statistical thermodynamics, used to find a subtle addition to the definition of entropy Second Law of Thermodynamicso In any spontaneous process, the total entropy change of the universe is positive∆ Su>0 and ∆ Su=∆ Ssys+∆ Ssurro Entropy change for the surroundings, ∆ Ssurr=−∆ HTo Thermolysis – advanced recycling or feedstock recycling, recovered monomer canbe purified by distillation or other means Third Law of Thermodynamicso The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero, T=0 ° Ko Impossible to attain a temperature of absolute zeroo Standard molar entropy, S°- determining the change in entropy of a given chemical substance from 0 K to 298 K at pressure of 1 atmo∆ S°=∑iviS°( product )i−∑jvjS°(reactant)jLecture 19 (October 28)Free Energy and Chemical Reactions Gibbs Free Energy, Go A way to predict spontaneous processeso∆ G=∆ H−T ∆ STable 1: possibility of spontaneitySign of ∆ HSign of ∆ SSpontaneityNegative (exothermic) Positive At all temperaturesPositive Negative NeverNegative (exothermic) Negative Only at low temperaturesPositive Positive Only at high temperatureso Exothermic reactions, ∆ H <0, is preferred over endothermic reactionso Reactions where ΔS > 0 are preferredo Enthalpy driven  Processes occurring spontaneously at low temperatures Enthalpy term causes ΔG to be negativeo Entropy driven Where the –TΔS term is larger than the ΔH termo Gibb’s free energy is equal to the maximum amount of useful work∆ G=−wmaxo Reversible  System is near equilibrium, so a small change in a variable will bring the system back to its initial stateo Irreversible System cannot be restored to initial stateo Standard Gibbs free energy change, ∆ G°- free energy change under these conditions∆ G°=∑iviGi°( product )i−∑jvjGj°(reactant)jLecture 20 (October 30)Rates of Reactions Ozone Depletiono Chapman cycle – proposed by British scientist in 1903 1st step is the photochemical dissociation of O2 to form oxygen atoms,which then react and form ozone, O3 Decrease of ozone concentration over Antarctica and North Americao Ozone is considered a pollutant in the troposphere but beneficial in the stratosphereo Ozone hole isn’t permanent Rates of Chemical Reactionso Reaction rate - ratio of the change in concentration to the elapsed timerate=change∈concentrationelapsed time=∆[substance ]∆ tv∏¿ ∆ t∨rate=−∆ [reactant ]∆t=−∆[reactant ]vreact∆ trate=∆ [ product ]∆ t=∆ [ product ]¿o Average rate – two concentrations are measured at times separated by a finite difference, and the slope of the line between them gives the rate i.e. – traveling 400 miles in 10 hours, avg rate = 40 mpho Instantaneous rate – refers to the rate at a single moment, and it is given by the slope of a line tangent to the curve defined b the change in concentration versus time i.e.- at hour 1, traveling at 54 mph and at hour 4, traveling at 34 mph Rate Lawso Rate Law – mathematical equation showing the dependence of reaction rate on concentration Differential rate law – derived from calculus-Rate=k[X]m[Y]n- The actual values of the


View Full Document
Download Exam 3 Study Guide
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Exam 3 Study Guide and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Exam 3 Study Guide 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?