1. Bellwork Wednesday
Determine if the following are endothermic or exothermic.
H = kJ/mol
H = kJ/mol
H = kJ/mol
H = kJ/mol

2. Unit 10 Ch 17 Part 4

3. Heat of vaporization and heat of condensation. They are equal amounts!
Heat of fusion and heat of solidification. They are equal amounts!

4. Heating/Cooling Curve shows energy changes
Heating/Cooling Curve shows energy changes. All matter follows curve when energy is added or lost.
Csteam= 2.1 J/g oC or .5 cal/goC
∆Hvap =∆Hcond =2260J/g
Cwater= 4.18 J/g oC or 1.00 cal/goC
∆Hfus = ∆Hsolid= 334J/g
CIce= 2.0 J/g oC or .5 cal/goC

5. At these points, temperature is CONSTANT!!!

6. 17. 3 Phase Changes -change of physical state Ex
Phase Changes -change of physical state Ex. Melting, freezing, evaporation, condensation, sublimation, deposition -The temperature of a substance does not change during a phase change.

7. Question
Why is the slope between ice and vapor so long on the heating curve?

8. Sublimation- Change of a solid to a gas without going through the liquid phase Deposition is the opposite Ex. Iodine, ice cube “shrinkage”, freeze drying, freezer burn

9. Exothermic - energy is a product ∆H Endothermic - energy is a reactant +∆H  H is also called the heat of reaction or Enthalpy

10. Heat
Horizontal portions of the curve indicate a physical state change. Notice that the temperature does not change in these regions! However, there a a change in particle position resulting in a change in potential energy.
Heating/Cooling Curve
-Shows energy changes of matter. All matter follows a curve when energy is added or lost.
Slope portions show temperature change which indicates a change in kinetic energy as well.

11. Ex. How much heat, in calories, is needed to melt 150. g of ice at 0oC?
No temp change (just phase change) Molar heat of fusion = 334 J/g for H2O q=(150.g)(334 J/g) = 50100J 1 cal = J 4.18 J = 1.20 x 104 calories

12. Ex. How much heat, in calories, is needed to heat the liquid water in the above problem to 20.oC?
No phase change (just temp. change) q = mC T q = (150.g)(1.00 cal/goC)(20.C) q = 3.00 x 103 calories

13. Ex. A 50. g sample of ice is held at -10. oC
Ex. A 50. g sample of ice is held at -10.oC. Will 270 calories of heat be sufficient to raise the temperature of the ice to 0oC?
just temp change
q = mC T
q = (50.g) (0.5 cal/goC)(10.oC)
q = 250 calories, Yes

14. Ex. How many calories are released when 36 g of steam at 100
Ex. How many calories are released when 36 g of steam at 100.oC condenses to water at 100.oC?
just phase change q=mHv q= (36g) (2260 J/g)= 81360J 1 cal = J = 1.9 x 104 calories

15. Ex. How many calories are needed to convert 5
Ex. How many calories are needed to convert 5.0 g of ice at -15oC to steam at 130oC?
Phase changes and temp changes
q = (5.0g)(0.5cal/goC)(15oC)
= 38 calories
q= (5.0g)(334 J/g)= 1670 J cal
= J
= 4.0 x 102 calories (continued)

16. q =( 5. 0g) (1. 0 cal/goC)(100oC) = 500 calories q= (5
q =( 5.0g) (1.0 cal/goC)(100oC) = 500 calories q= (5.0g )(2260 J/g)= 11300J 1cal = J = 2.7 x 103 calories q = (5.0g) (1.0cal/goC)(30oC) = 150 calores q = = 3713 calories

17. Standard Heat of Formation of a compound ( Hfo)
* Hfo of a free element in its standard state is zero. *This is another way to calculate  H for a reaction.  H =  Hfo products -  Hforeactants
*(a table of standard heats of formation will be provided)

18. ∆H = 178.4 kJ (endothermic-absorbs energy)
Ex Calculate  H for the following reaction: CaCO3(s)  CaO(s) CO2(g)
∆Hfo values: CaCO3 = kJ/mol CaO = kJ/mol CO2 = kJ/mol
∆H = [1∙ ∙ )] – [1 ∙ ]
∆H = kJ (endothermic-absorbs energy)

19. ∆H = [2 ∙ (-241.8)] – [2∙ 0 + 1 ∙0] ∆H = -483.6 kJ
Calculate the heat of reaction for the following reaction: 2H2(g) O2(g)  2H2O(g)
∆Hfo values: H2O(g) = kJ/mol
∆H = [2 ∙ (-241.8)] – [2∙ ∙0]
∆H = kJ
(exothermic- releases
Energy)
Remember to multiply heat values by coefficients!!!

20. Bellwork Summary Part 4 first!!! Friday
Calculate the enthalpy of formation for the reaction below.
Zn(s) HCl(aq)  ZnCl2(aq) + H2(g)
H HCl = kJ/mol
H ZnCl2 = kJ/mol

21. Review day Another multi step problem
How much energy in joules is required to convert 50.5 g of ice at -5.5 °C to water at 85.0 °C?