1. Announcements If you don’t have a clicker with you, sign in after class If you don’t have a clicker with you, sign in after class Tutoring hours this week: Tutoring hours this week: Monday 12:00-2:00pm Tuesday 10:00am -12:00pm; 2:00-3:00pm; 5:30-8:30 pm Wednesday 2:00-5:00pm and 5:30-8:00pm Quote of the day: The quality of mercy is not strain'd, It droppeth as the gentle rain from heaven Upon the place beneath: it is twice blest; It blesseth him that gives and him that takes:

2. Lab This Week  IR Spectroscopy (Room 203)  Molecular Modeling (Room 202)  Part 2 of last week’s lab:

3. Last time…  Hess’ Law:  Enthalpies can be added  If reaction is reversed, sign is reversed  If reaction is multiplied by integer, enthalpy is too  Constant pressure calorimetry (lab last week)

4. Constant Volume Calorimetry (“Bomb”) N 2 H 4 + 3 O 2  2 NO 2 + 2 H 2 O E released = E absorbed by water + E absorbed by calorimeter E water = E calorimeter = Total E =  H = energy/moles = 0.500 g N 2 H 4 600 g water 420 J/ o C

5. Calculating Reaction Enthalpies from Known Data  Use values that have been determined from experiment  Two types of data that can be used  Standard enthalpies of formation (Chapter 5.6)  Bond enthalpies (Chapter 8.4, pp. 8-10 to 8.13)

6. Standard Enthalpy of Formation  Standard conditions: substance in pure form, 1 bar pressure, usually at 298K (25°C)  Heat of formation for an element in its most stable form is zero  Heat of formation for a compound = the energy required to form a compound from its constituent elements in their most stable form  Standard heat of formation is given in Joules per mole  Results in fractional coefficients on occasion

7. Table 5-2, p. 195

8. Using Standard Enthalpies of Formation  What is the  H rxn for the detonation of nitroglycerin?  How much energy is released when 10g is detonated?

9. Bond Enthalpy  Remember that bond energy is the amount of energy required to break a bond in a gas phase molecule  Can only use bond enthalpies for reactions in which everything is in the gas phase  When calculating  H using bond enthalpies, assume all bonds are broken in the reactants (  H= +) and formed in the products (  H= -)

10. Using Bond Enthalpy to Calculate  H rxn