W20-Review-Lectures-18-22.pdf - Recap of kinetic model...

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3/16/201Chemistry 260W2020Review of Lectures 18 – 22Kinetic theory of gases, 1stlaw of ThermodynamicsEnthalpyThermochemisrySee the last announcement in CANVAS for the revised plans for the course.Quiz deadlinesProblem set due datesMidterm #2Post-lecture quiz Connects microscopic properties (speed,# collisions, etc.) to macroscopicproperties (volume, pressure,temperature, etc.)PV=nRTPressure andspeed ofmoleculesrelated32transBEk T=Temperature is essentially a measure of the average kinetic energyof the atoms/molecules in the gasRecap of kinetic modelBased on ideal gas assumptions:• Molecules are very small, don't interact,have random motion, elastic collisions• Pressure is related to speed• Temperature is related to averagekinetic energy231PVumN=BtranskTE32=The energy of an ideal gas does not depend on the volume.()222122222122111222112211332223(for a monoatomic ideal gas).2NNrmsUmvmvmvm vvvNmvRTNmvnMnRTMUnRT=+++=+++====Þ=!!The Internal Energy of a Monoatomic GasIntensive or Extensive?Intensive quantitiesPressureTemperatureDensityExtensive quantitiesEnergymass/number of molesVolumeExtensive properties depend on the extentof material Intensive properties stay the same when “doubling” the systemP,V,n,T,EP,V,n,T,EP,2V,2n,T,2E
3/16/2021. WORK:deposit of energy into the uniform macroscopic motions of matter – flow of kinetic and potential energy w = -PEXDV2. HEAT: deposit of energy into the random microscopic motions of matter – flow of thermal energySystemHEATSystemHEATq < 0q > 0ExothermicEndothermicWork and Heat are both FLOWSof energy. àThey are pathfunctions, NOT properties of state.àThey are not possessed by the system.àThey are defined in terms of a process.EnergyHeatWorkDU = q + wIt is frequently most convenient to carry out a process at constantpressure.• Cooking dinner• Drying the laundry• Digesting dinner• Synthesizing a compound in labAt constant pressure if only PV work is done:The enthalpy change is the heat transferred ina process at constant pressure (assuming onlyPV work).

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