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CSU CHEM 113 - Exam 1 Study Guide

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Chem 113 1st EditionExam # 1 Study Guide Lectures: 1 – 8Lecture 1 (January 23)What is a spontaneous process? What is a nonspontaneous process?A spontaneous process is a change that occurs without a continuous input of energy from outside of a system. A nonspontaneous process is a change that occurs only if the surroundings continuously supply energy to the system. If a change is __________________ in one direction it will be ___________________ in the reverse direction.Spontaneous; nonspontaneousWhat is freedom of particle motion? Does freedom of motion increase or decrease in an endothermic process?Freedom of particle motion is associated with a change in physical states (ie gaseous stages have the highest freedom of motion). Endothermic processes result in an increase of the freedom of motion.What is entropy? How is it calculated? Does entropy increase or decrease in an endothermic process?Entropy is the measure of how particles are dispersed. S=kBlnW; S is entropy, W is the number of microstates, kB is the Boltzmann constant. Entropy increases during endothermic processes.Lecture 2 (January 26)What is the entropy of a perfect crystal at absolute zero? Explain.A perfect crystal at absolute zero has zero entropy; there’s minimal energy at absolute zero because there’s only one microstate.What are the conventions that need to be met for a substance’s standard molar entropy to be measured (the conventions for a standard state)?The substance must be 1 bar for pure gases, 1M for solutions, it must be in its most stable form for solids and liquids, and it must be at a temperature of 25°C or 298 K.What are the factors that affect entropy? What are the patterns in entropy for each of these factors?Temperature, the substance’s physical state, the formation of a solution (ie salts/liquids or gasses), and the atomic size and molecular complexity. As temperature increases, there are more microstates and freedom of motion, causing entropy to increase. As temperature decreases, there are less microstates and freedom of motion, causing entropy to decrease. Entropy increases as it changes from solid to liquid to gas. The entropy of salts and liquids increases in a solution, while the entropy of gasses decreases in a solution. A large atomic size increases entropy, and more possible motions of the atom (complexity) increases entropy. Ring structures have less entropy than the corresponding chain structures. NOTE: these patterns only apply to substances in the same physical state.Lecture 3 (January 28)Entropy of the universe_______________ for a spontaneous process, but ________________ for a nonspontaneous process.Increases; decreases.ΔS°sys is __________ if the amount of gas increases.Positive.ΔS°sys is ___________ if the amount of gas decreases.Negative.ΔS°sys is ___________________ if a new structure forms that has more freedom of motion.Likely to be positive.How is the Second Law of Thermodynamics applied to spontaneous processes?All real process occur spontaneously in the direction that increases the entropy of the universe. In order for a process to be spontaneous, a decrease in the entropy of the system must be offsetby a larger increase in the entropy of the surroundings or vice versa.How do entropy changes effect the surroundings?In exothermic processes, the surroundings absorb the heat and the entropy of the surroundings increases. In endothermic processes the surroundings provide the heat absorbed by the system and the entropy of the surroundings decreases.What is the equation used to calculate the standard entropy of a reaction?ΔS°rxn=ΣmS°products- ΣnS°reactantsHow does the temperature at which heat is transferred effect the entropy of the surroundings? What is the equation used to calculate this?The impact on the entropy of the surroundings is larger when the surroundings are at a lower temperature because there is a greater relative change in the entropy of the surroundings.ΔSsurr=−qsysT∨ΔS surr=−ΔHsysT.Lecture 4 (January 30)What are the components of entropy for spontaneous reactions?For an exothermic reaction in which the change in entropy of the system is positive, the size of the change in entropy of the surroundings doesn’t matter since the change in entropy of the surroundings is positive for all exothermic reactions; therefore, this kind of reaction will always be spontaneous.For an exothermic reaction in which the change in entropy of the system is negative, the changein entropy of the surroundings must be smaller than the change in entropy of the system for thereaction to be spontaneous.For an endothermic reaction in which the change in entropy of the system is positive, the change in entropy of the surroundings must be smaller than the change in entropy of the system for a reaction to be spontaneous.The change in entropy of the surroundings is always negative for endothermic reactions.What is the relationship between the change in free energy and entropy?ΔGsys=-T ΔSuniv; the sign of ΔGsys and ΔSuniv are opposite.How does the change in free energy determine the spontaneity of a process? What is the equation used to determine this?If the change in free energy is poisitive, it is a spontaneous process. If the change in free energy is negative, it is a nonspontaneous process. If the change in free energy is equal to zero, the process is at equilibrium. ΔGsys= ΔHsys-T ΔSsys.What is the equation used to calculate the change in free energy from a chemical equation?ΔGrxn=ΣmΔGproducts-ΣnΔGreactantsLecture 5 (February 2)What does the change in free energy mean in terms of work?The change in free energy is the maximum useful work done by a system during a spontaneous process at a constant temperature and pressure. The change in free energy is the minimum work that must be done to a system to make a nonspontaneous reaction at a constant temperature and pressure. A reaction at equilibrium can no longer do work.Lecture 6 (February 4)Fill in the missing parts of the table.ΔH ΔS TΔS ΔG Description- + + -+ - - ++ + + + or -- - - + or -Always spontaneous, at any temperature; Never spontaneous, at any temperature; Spontaneous at high temperatures; Spontaneous at low temperaturesWhat are the effects of temperature on reaction spontaneity?The reaction becomes spontaneous as temperature increases because the change in free energybecomes more negative (if the change in heat of the reaction and change in entropy of the reation are


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