CHEM 102 1nd Edition Lecture 6 Outline of Previous Lecture I. Heat Units and EquationsII. Calculating ΔHOutline of Current LectureI. Bond EnergyII. ThermodynamicsIII. First Law of ThermodynamicsCurrent LectureI. Bond Energy- Bond energy is the energy required to break one mole of bond in a gas- This is also known as bond enthalpy because heat must be added to break a bondo Bond-breaking is endothermic (+)o Bond-making is exothermic (-)o ΔHrxn = BEbreak - BEmake ΔH is the amount of heat needed to be put in or taken away BEbreak is the bond energy of the atoms that need to be broken BEmake is the bond energy of the atoms that need to be made Ex. Calculate the enthalpy change for CH4 + 3Cl CHCl3 + 3 HCl Draw the compounds first Then, add up the number of bonds and what they are that need to be broken and made Break: 4 C-H, 3 Cl-Cl, so 4 x 410 + 3 x 243 = 2369 Make: 3 C-Cl, 3 H-Cl, so 3 x 330 + 3 +432 = 2696 BEbreak –BEmake = 2369 – 2696 = -327 kJII. Thermodynamics- Standard state is:o Most stable state at 1 atm and specified temperatureThese 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.o Only Liquids in standard state are Bromine and Mercuryo Gases are: hydrogen, oxygen, nitrogen, fluorine, chloride, and 8th familyo For solute; standard state is a 1 M concentrationIII. First Law of Thermodynamics- Energy in universe is constant- ΔEuniv = ΔEsys + ΔEsurr = 0- ΔEsystem = Q + wo Q is the heato W is work = -PΔV or –(Δn)RT Where in is the change of moles of gas R is a constant And T is temperatureo Work is positive when done ON systemo Work is negative when done BY
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