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KU CHEM 170 - Entropy
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Chem 170 1st Edition Lecture 17Outline of Last Lecture I. Last Lecture: Osmotic PressureII. Van’t Hoff FactorIII. ElectrolytesOutline of Current Lecture IV. Spontaneous and Non-spontaneousV. Spontaneity and Exothermic ReactionsVI. EntropyCurrent LectureChapter 14 – Entropy and Free Energygoal: to be able to predict if a process is spontaneous or notSpontaneous describes a process that occurs in a system left to itself. Non-spontaneous describes a process that will not occur unless some external action is continuously applied.For example, 4 Fe(s)+3 O2(g)→ 2 Fe2O3(s) the rust reaction is spontaneous. While the reverse reaction 2 Fe2O3(s)=4 Fe(s)+3 O2(g) is non-spontaneous.If the forward process is spontaneous, then backward process is non-spontaneous.Both the spontaneous and the non-spontaneous processes are possible.Spontaneity and Exothermic ReactionsIn the old times, spontaneity was predicted by looking at whether a reaction was exothermic. For example, combustion reactions (solid +O2→C O2+H2O) are exothermic. People also looked at the potential energy for spontaneity. For example, a ball on a hill would have a lot of potential energy and it can spontaneously roll down the hill. However a ball at the bottom of the hill would not be able to spontaneously roll up the hill.BUT endothermic reactions can also be spontaneous. For example,H2O(s )→ H2O(l) is spontaneous and endothermic. Therefore focus on the questions: Does the system gain or loose energy (ΔH)? And What is the degree of disorder in the system (entropy)?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Entropy (S) is a thermodynamic property related to the degree of disorder. The greater the randomness or disorder the greater the entropy.Demonstration: SCN¿¿Ba(OH )2∙ 8 H2O+2 N H4SCN(s)→ Ba ¿ is an endothermic reaction. If water is placed on a block of wood and the reaction takes place on a beaker sitting on top of the water and the wood the temperature would decreaseto the point where the water would freeze and adhere the wood to the beaker.Ludwig Boltzmann (1844-1906) was a scientist that liked to drink.S=kln(W), where S is entropy, k is Boltzmann’s Constant (1.38×10-25) and W is the number of


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KU CHEM 170 - Entropy

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