Lecture 36 - Topics for the day Administrative stuff...

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Topics for the day Administrative stuff Thermodynamics DeFnitions ±irst Law of thermodynamics Energy Heat Thermochemistry Enthalpy The end approaches. .. April/May Sun Mon Tue Wed Thu Fri Sat 18 19 20 21 22 23 24 Lecture 36 Lecture 37 Lecture 38 Quest 5 due Quest 6 starts 25 26 27 28 29 30 May 1 Lecture 39 ALEKS 6 due ALEKS 7 starts Lecture 40 Lecture 41 Quest 6 due May 2 May 3 May 4 May 5 May 6 May 7 May 8 Lecture 42 Lecture 43 EXAM FOUR Lecture 42 ALEKS 7 due ALEKS pie opens May 9 May 10 May 11 May 12 May 13 May 14 May 15 May 16 May 17 May 18 May 19 May 20 May 21 May 22 FINAL EXAM ALEKS pie closed Aiming to skip the fnal? Decision is made on May 5th. Quest homework grade changes Exam questions Rank these molecules: CH 3 ± C 2 H 6 H 2 O H 2 He in terms of increasing viscosity Answer: He, H 2 , C 2 H 6 , CH 3 ± , H 2 O The question was asked how should we know that He < H 2 ? ±rom the periodic trend of atomic radii, effective screening increases across a row, and so we know that He < H. If He < H, then certainly He < H 2 Also, although there are the same number of electrons in He and H 2 : ±or He, the two electrons are in a 1s atomic orbital. ±or H 2 , the two electrons are in a 1 σ molecular orbital, which is larger. Also, the two electrons in H 2 are not bound as tightly as the two electrons in He, so they are more easily polarizable, i.e., stronger dispersion forces. 1 2 3
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Balloons Balloon color Observation on lighting balloon Which gas? Yellow Quiet pop White Soft pop, small Fame Pink Bang, lots of Fames Purple Louder bang, Fash Maroon Loudest bang, more Fash Clear Bang and sparkle 2H 2 + O 2 2H 2 O You know how to draw these molecular structures. You know how to take reactants and products and write a stoichiometrically balance chemical reaction based on the conservation of mass and charge. But those two things didn’t tell you anything that would lead you to expect an explosion. He O 2 H 2 H 2 :O 2 = 1:1 H 2 :O 2 = 2:1 H 2 , Mg(s) Thermodynamics Thermodynamics is the study of energy changes in a system. Thermodynamics addresses three main questions: Will a reaction occur? If a reaction occurs, what energy changes are involved? If a reaction occurs, to what extent will the reaction go? to completion? This is our topic for the rest of the semester. It is math-intensive, and considered by most as the hardest topic of the four we’ve covered. Hang in there! Thermodynamics is not concerned with the rate of reaction (how quickly the reaction occurs). That is the study of reaction kinetics . In thermodynamics, we divide things into system and surroundings. The
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Lecture 36 - Topics for the day Administrative stuff...

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