ChemTeacher

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AP Chemistry – Class 33

CalorimeterDates

  • Periods E/ F – Wednesday, November 7th

Details from Quiz

  • no need to write full sentences
  • mole fractions and ratios – leave as decimals

Lab Takeaway #1:  Delta E = 0

  • the system (substances dissolved in water) and the surroundings (water) exchange energy, facilitated by the calorimeter
  • we measure the surroundings, not the system

Lab Takeaway #2: Delta H = Q (@ constant pressure)

  • enthalpy is difficult to grasp (H = E + PV)
  • most processes (and all in this class) are at constant pressure
  • we want the DH of a process so we use the Q of the process, which is the opposite of the Q of the surroundings

Lab Takeaway #3: Q = mcDT

  • simple formula, powerful implications
  • “c” is the specific heat capacity  and is particular to a substance
  • units follow the equation, not the other way around
  • water is difficult to heat, lots of Q needed to make DT big

Lab Takeaway #4: DH is proportional to moles

  • Finding heat flow, and therefore DH, shows that it is proportional to the moles of substance used
  • the DH for a process can be treated the same as we would treat other molar quantities

New Idea: Work on a PV graph

  • W = -PDV only applies if Pext is constant
  • On a P vs V graph the work is area under the curve
  • can determine the work using the graph
  • practice the idea

Homework

  • We will work on problems handed out during next class
  • Students should finish by the end of the next class

Information

This entry was posted on November 7, 2012 by in CAgenda, Chemistry and tagged , .

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