1. Unit 12 Review

2. Be Able to…
Describe the following for a substance in its solid, liquid and vapor state:
Molecule orientation
Relative amounts of Kinetic Energy (KE)
Strength of the forces between the molecules
And describe what happens to the molecules of a substance as it undergoes different phase changes
Identify methods of heat transfer
Tell whether a phase change is endothermic or exothermic
Tell whether a reaction is endothermic or exothermic in various ways (by calculation and by looking at a diagram)
Perform the needed energy calculations for DHrxn (***Formulas and constants will be given***)
Predict whether entropy is increasing or decreasing
Calculate DG and Q

3. Identify the types of heat transfer that occur in the following scenarios.
A. B.
C. Answers:
A. convection
B. radiation
C. conduction

4. Heating Curves

5. 0oC - 65oC; it is in the solid state
Observe the heating curve below: Between what two temperatures would substance B have the lowest amount of particle movement?
Temp oC
250
220 65 45
Substance A
Substance B
0oC - 65oC; it is in the solid state

6. Observe the heating curve below: If substance A is heated from 32oC to 220oC, which phase changes (if any) will it undergo?
Temp oC
250
220 65 45
Substance A
Substance B
Melting

7. Ethanol; it has the lowest specific heat
substance
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
Which substance would be the easiest to heat up?
Ethanol; it has the lowest specific heat

8. Ethanol, ammonia, water; increasing values of DHFUS
substance
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
Rank the substances in (ascending) order of how quickly they would melt if given the same amount of each and constant heat was applied evenly?
Ethanol, ammonia, water; increasing values of DHFUS

9. Water; it has the highest DHVAP Remember: DHCON = -DHVAP
substance
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
Which substance above would release the most energy when it condenses from a vapor to a liquid?
Water; it has the highest DHVAP
Remember: DHCON = -DHVAP

10. Which substance above takes the least amount of heat per mole to melt?
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
Which substance above takes the least amount of heat per mole to melt?
ethanol

11. substance
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
Which substance above takes the most amount of heat per mole to vaporize?
water

12. substance
DHFUS
DHVAP
Cliquid
water, H2O
6.01 kJ/mol
40.7 kJ/mol
4.184 J/goC
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
2.44 J/goC
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
4.52 J/goC
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
Which substance above requires the most amount of heat to raise its temperature by 5 K ?
ammonia

13. Q and DHrxn questions/calculations
Get out the notes with data about water, ethanol, and ammonia

14. How much heat is released when 2.00 moles of water freeze?
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
12.0 kJ of heat
released

15. How much heat is absorbed when 5.00 moles of ammonia vaporize?
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol
117 kJ of heat

16. How much heat is released when 34.0g of ammonia condenses?
Convert grams of ammonia to moles of ammonia
Convert moles of ammonia to kJ; Use DHvap
About 46.6 kJ of heat released
substance
DHFUS
DHVAP
water, H2O
6.01 kJ/mol
40.7 kJ/mol
ethanol, C2H5OH
4.94 kJ/mol
38.6 kJ/mol
ammonia, NH3
5.66 kJ/mol
23.3 kJ/mol

17. What is the specific heat of a substance whose temperature changes from 35.0oC to 78.5oC when it absorbs 625 J of heat if its mass is 45.6g?
Use Q = mcDT
0.315 J/goC

18. How much energy is absorbed if 10
How much energy is absorbed if 10.5 g of liquid water has a temperature change from 15.0oC to 80.5oC? (the specific heat of liquid water is 4.18 J/goC)
Use Q = mcDT
2870 J/goC

19. 33. 0 g of water at 5. 00 degrees Celsius is added to 48
33.0 g of water at 5.00 degrees Celsius is added to 48.0g of water at 45.0 degrees Celsius. What is the final temperature of the water mixture?
Qwater1 = -Qwater2
28.7oC

20. How much heat does the activated complex have in the reaction diagrammed above?
250 kJ

21. What is the activation energy required to make this reaction happen?
200 kJ

22. What is the DHrxn for this particular reaction?
50 kJ

23. Is this reaction endothermic or exothermic?
Endothermic; the products have a higher potential energy than the reactants.

24. Calculate the DHrxn of the reaction of ethane (C2H6) with oxygen gas which forms carbon dioxide and water vapor. Is it an exothermic or endothermic rxn?
2C2H6 (g) + 7O2  4CO2 + 6H2O
DHrxn = Products – Reactants (*Get values from chart)
-2858 kJ
Exothermic

25. Calculate the DHrxn for the vaporization of water into vapor
Calculate the DHrxn for the vaporization of water into vapor. Is it an exothermic or endothermic process?
H2O(l)  H2O(g)
DHrxn = Products – Reactants (*Get values from chart)
44 kJ
Endothermic

26. Spontaneity and Free Energy (S and G)

27. Predict the sign of S for the following reactions:
ClF(g) + F2(g)  ClF3(g)
H2O(l)  H2O(g)
2SO3(g)  2SO2(g) + O2(g)
S = (-), S < 0
S = (+), S > 0

28. Calculate the DG for a reaction occurring at 298K in which the enthalpy is -266 kJ/mol and the entropy is 65.0 J/K. Is it thermodynamically favorable or unfavorable?
DG = DH - TDS
Units must match
-285 kJ/mol
Thermodynamically favorable

29. Calculate the entropy for a reaction when DG is 2855 kJ/mol and DH is 788 kJ/mol at 300.0K. Is this reaction thermodynamically favorable or unfavorable?
DG = DH - TDS
Solve for DS
DS = kJ/K
Thermodynamically unfavorable