1. Question of the Day
1. A 1.0 mole sample of ethanol (C2H5OH) has a heat capacity of J/°C. Calculate the specific heat of ethanol (hint: What is the relationship between heat capacity and specific heat?)
Day
= 2.4 J/g°C

2. Energy Enthalpy Entropy Spontaneity
Thermodynamics
Energy
Enthalpy
Entropy
Spontaneity

3. State Functions
Property determined under specified conditions of T, P, location, etc
Independent of HOW conditions are reached

4. State Functions Examples
_____________________________________ B B
DE = difference
between A & B
Energy d A A

5. State Functions: Hess’s Law
For a reaction that occurs in several steps, the sum of the D’s for each step is the D for the net reaction.
Thus, it is possible to calculate D for a complex reaction by adding the D’s of each simple reaction that leads to the complete reaction.

6. State Functions: Hess’s Law
The Equation
DTOTAL = Dstep 1 + Dstep 2 + Dstep 3 + … + Dstep n

7. Energy Transfers: Possibilities: How heat transfer is made:
From system to surroundings
From surroundings to system
How heat transfer is made:
Heat = q
Positive change = heat added to system
Negative change = heat released from system
Work = w
Positive change = work done ON system
Negative change = work done BY system 7

8. Energy Transfers First Law of Thermodynamics
Energy lost by the system EQUALS energy gained by the surroundings
Energy gained by the system EQUALS energy lost by the surroundings 8

9. Energy Transfers Exothermic Change system surroundings Loss increases
Energy moves from ______________ to ________________
_________ of q
Temperature of surroundings ________________
system
surroundings
Loss
increases

10. Energy Transfers Endothermic Change surroundings system Gain decreases
Energy moves from ________________ to _____________
_________ of q
Temperature of surroundings ________________
surroundings
system
Gain
decreases

11. Energy Transfer Equations
Internal Energy: DE = Ef – Ei
Ef = final energy
Ei = initial/starting energy
Energy Change due to Heat & Work: DE = q + w
Use + q if endo
Use – q if exo
Use + w if work is done ON system
Use – w if work is done BY system

12. Review section 17.1 and complete #s 5-11 on page 561.
Assignment
Review section 17.1 and complete #s 5-11 on page 561.
- Due Monday 2-22

13. Assignment
Review section 17.1 and complete #s 42, 43, 45, 47, 48, and on page 586.
- Due Thursday 2-25

14. Question of the Day
1. The specific heat of ice is 2.1 J/g°C. What is the heat capacity for a 2.0 mole sample?
Day
= 75.6 J/°C

15. Enthalpy
Thermodynamic property that measures/describes the changes in heat content of a system under constant pressure.
Symbol:
Units of measure:
Equations and usage
H, DH
cal, kcal, J, kJ
State function
DH = Hf - Hi
+DH
Hf > Hi
Heat gained & endo
-DH
Hf < Hi
Heat lost & exo

16. BOOK - Calorimetry Constant-Pressure Calorimeters
The enthalpy (H) of a system accounts for the heat flow of the system at constant pressure.
The heat absorbed or released by a reaction at constant pressure is the same as the change in enthalpy, symbolized as ΔH.

17. BOOK - Calorimetry Constant-Pressure Calorimeters
The value of ΔH of a reaction can be determined by measuring the heat flow of the reaction at constant pressure.
In this textbook, the terms heat and enthalpy change are used interchangeably.
In other words, q = ΔH.

18. Calculating Enthalpy Change in Reactions
Formula:
DHRXN = DHPRODUCTS - DHREACTANTS
2 H2(g) + O2(g)
__________________________
2 H2O(g)
Higher E means
Less stability – +
483.6
Lower E means
more stability

19. Calculating Enthalpy Change in Reactions
CH4(g) + 2O2(g)
CH4(g) + 2O2(g) + –
802 + –
890 H
CO2(g) + 2H2O(g)
CO2(g) + 2H2O(l)

20. Calculating Enthalpy Change in Reactions
Phase matters!!!!!!!
Heat In = Heat Out

21. Thermochemical Equations
How can you express the enthalpy change for a reaction in a chemical equation?
In a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product.

22. Thermochemical Equations
In the equation describing the exo reaction of calcium oxide and water, the enthalpy change can be considered a product.
CaO(s) + H2O(l) → Ca(OH)2(s) kJ
Calcium oxide is one of the components of cement.

23. Thermochemical Equations
A chemical equation that includes the enthalpy change is called a thermochemical equation.
CaO(s) + H2O(l) → Ca(OH)2(s) kJ

24. Thermochemical Equations
Heats of Reaction
The heat of rxn is the ΔH for the chemical equation exactly as it is written.
Heats of reaction are reported as ΔH.
The physical state of the reactants and products must also be given.
The standard conditions are that the reaction is carried out at kPa (1 atm) and 25°C.

25. Thermochemical Equations
Heats of Reaction
Each mole of calcium oxide and water that reacts to form calcium hydroxide produces 65.2 kJ of heat.
CaO(s) + H2O(l) → Ca(OH)2(s)
ΔH = –65.2 kJ
In exothermic processes, the chemical potential energy of the reactants is higher than the chemical potential energy of the products.

26. Thermochemical Equations
Heats of Reaction
Baking soda decomposes when it is heated. This process is endothermic.
2NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g)
The carbon dioxide released in the reaction causes muffins to rise while baking.

27. Thermochemical Equations
Heats of Reaction
2NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g)
Remember that ΔH is positive for endothermic reactions. Therefore, you can write the reaction as follows:
2NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g)
ΔH = 85 kJ

28. Thermochemical Equations
Heats of Reaction
The amount of heat released or absorbed during a rxn depends on the number of moles of the reactant involved.
The decomposition of 2 mol of sodium bicarbonate requires 85 kJ of heat.
Therefore, the decomposition of 4 mol of the same substance would require twice as much heat, or 170 kJ.

29. Thermochemical Equations
Heats of Reaction
To see why the physical state of the reactants and products must be stated, compare the following two equations.
difference = kJ
H2O(l) → H2(g) + O2(g) ΔH = kJ 1 2
H2O(g) → H2(g) + O2(g) ΔH = kJ

30. Using the Heat of Reaction to Calculate Enthalpy Change
Sample Problem 17.4
Using the Heat of Reaction to Calculate Enthalpy Change
2NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g)
Calculate the amount of heat (in kJ) required to decompose 2.24 mol NaHCO3(s).

31. Assignment
Review section 17.1 and complete #s 42, 43, 45, 47, 48, and on page 586.
- Due Thursday 2-25

32. Question of the Day The appropriate unit for specific heat =
Ice subliming (solid  gas) is exo or endo?
Day

33. PRACTICE:
2NaHCO3(s) + 85 kJ → Na2CO3(s) + H2O(l) + CO2(g)
Calculate the amount of heat (in kJ) required to produce 3 mols of Na2CO3(s).
If a sample of NaHCO3(s) requires kJ to completely decompose, what was the mass of the original sample?
= 255 KJ
= 252 g

34. Thermochemical Equations
Heats of Combustion
The heat of combustion is the heat of reaction for the complete burning of one mole of a substance.

35. Thermochemical Equations
Heats of Combustion
Small amounts of natural gas within crude oil are burned off at oil refineries.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) kJ
This is an exothermic reaction.
Burning 1 mol of methane releases 890 kJ of heat.
The heat of combustion (ΔH) for this reaction is –890 kJ per mole of methane burned.

36. Heats of Combustion at 25°C
Interpret Data
Heats of Combustion at 25°C
Substance
Formula
ΔH (kJ/mol)
Hydrogen
H2(g)
–286
Carbon
C(s, graphite)
–394
Methane
CH4(g)
–890
Acetylene
C2H2(g)
–1300
Ethanol
C2H6O(l)
–1368
Propane
C3H8(g)
–2220
Glucose
C6H12O6(s)
–2808
Octane
C8H18(l)
–5471
Sucrose
C12H22O11(s)
–5645
Like other heats of reaction, heats of combustion are reported as the enthalpy changes when the reactions are carried out at kPa and 25°C.

37. Which of the following thermochemical equations represents an endothermic reaction?
A. Cgraphite(s) + 2 kJ Cdiamond(s)
B. 2H2(g) + O2(g) H2O kJ

38. Vocab. from the book: Heats of reaction Heats of combustion
Molar heat of fusion (melting)
Molar heat of solidification (freezing)
ΔHfus = -ΔHsolid

39. Vocab. from the book: Molar heat of vaporization
Molar heat of condensation
ΔHvap = -ΔHcond
Molar heat of solution (dissolving)

40. Assignment
Review section 17.1 and complete #s 42, 43, 45, 47, 48, and on page 586.
- Due Thursday 2-25

41. Question of the Day: EXO 16.2 kJ 3C2H2(g)  C6H6(l) + 630 kJ
Is this reaction endo OR exo?
How much heat is involved if you start with 2 grams of acetylene (acetylene = C2H2)?
Day
EXO 16.2 kJ

42. Spontaneity Main question of chemistry:
Will a reaction GO! when reactants are put together?
Spontaneous reactions
Reaction occurs by itself, activation E may be needed
May have fast, moderate, or slow rate
Non-spontaneous reactions
Require constant E supply to occur
Reaction stops when E supply is removed
Reversing reactions
If a reaction is spontaneous under specified conditions, the reverse is non-spontaneous at those same conditions

43. Predicting Sponaneity
Why is DH a pretty good predictor of spontaneity?
-DH : heat out
+DH: heat supply needed
When might DH not indicate spontaneity well?

44. Predicting Spontaneity
H2O(s) → H2O(l)
∆H = kJ;
1 atm, 0°C

45. Predicting Spontaneity
H2O(l) → H2O(g)
∆H = kJ;
1 atm, 100°C

46. Predicting Spontaneity
CaCO3(s) → CaO(s) + CO2(g)
∆H = kJ;
298 K vs K

47. Predicting Spontaneity

48. Entropy
Entropy is the measure of the disorder or randomness of a system.
Entropy is a state function.
Entropy changes follow Hess’ Law.
A system has high entropy if it
_____________________________________________
_______________________________________
(Very disorganized)
Is Very dsorigniaezd
Has freedom of motion

49. Entropy & Spontaneity
Reactions will be spontaneous if ________ is increased.
Examples
ice cubes melting vs. putting water in freezer to make ice cubes
room gets messy vs. doing work to put things in order
etnopry

50. Standards & Constants Conditions & Units
T = 25oC = 298K
P = 1 atm
Units: J/K = Joules/Kelvin
What is the relationship between entropy and temperature?
As T 0 K, S  0
T↓, S↓ and T↑, S↑

51. Standards & Constants
Why are the entropy values for elements and compounds always positive?
T always > 0K
Therefore everything is always moving
How do entropies compare among the phases of matter?
So solid < So liquid < So gas

52. Standard Entropy Changes
The equation
∆So = SSoproducts – SSoreactants
Example:
2HCI(aq) + 2Ag(s) → 2AgCl(s) + H2(g)1 atm, 25oC
Predict if this reaction will have + ∆So or – ∆So.
Calculate ∆So (NEED STANDARD VALUE HANDOUTS).

53. Standard Entropy Changes
The equation
So = SnSoproducts – SmSoreactants
Example:
2 H2(g) + O2(g) → 2 H2O(g) 1 atm, 25oC
Predict if this reaction will have + ∆So or – ∆So.
Calculate ∆So.

54. Assignment
Review section 17.1 and complete #s 42, 43, 45, 47, 48, and on page 586.
- Due Thursday 2-25

55. Question of the Day: NaCl(s) + 3.88kJ  NaCl(aq)
Is this reaction endo OR exo?
Draw an enthalpy diagram representing the change above:
NaCl(aq)
3.88 kJ – +
NaCl(s)

56. CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2 kJ
Practice:
1. If 32.6 kJ of heat are given off, how many grams of calcium hydroxide are produced?
CaO(s) + H2O(l) → Ca(OH)2(s) kJ
37 grams

57. Practice:
Use your standard values handout to determine the standard entropy change for the formation of nitrogen dioxide shown in the rxn below. THEN explain whether your calculation makes sense using what you know about predicting changes in entropy!
2NO(g) + O2(g) → 2NO2(g)
J/K

58. Assignment # 1 Unit 7 is due Friday 2-26!
# 11 Calculate ΔH for:
2F2(g) + 2H2O(l)  4HF(g) + O2(g)
H2(g) + F2(g)  2HF(g) ΔH = -537kJ
2H2(g) + O2(g)  2H2O(l) ΔH=-572 kJ
Assignment # 1 Unit 7 is due Friday 2-26!

59. Assignment:
#s 14 and 15 on page 567 (show work), #s 16, 17, 20, and 21 on page 568 (show work)
- Due Tuesday 3-1

60. Quick Talk: Enthalpy q Entropy Joules Potential Chemical Energy ΔS
State function ΔH
4.184 J
Specific heat

61. Question of the Day: Day 4 2-26 1. NaCl(s) + 3.88kJ  NaCl(aq)
Is this reaction endo OR exo?
Draw an enthalpy diagram representing the change above:
2. If 32.6 kJ of heat are given off, how many grams of calcium hydroxide are produced?
CaO(s) + H2O(l) → Ca(OH)2(s) kJ
3. Use your standard values handout to determine the standard entropy change for the formation of nitrogen dioxide shown in the rxn below. THEN explain whether your calculation makes sense using what you know about predicting changes in entropy!
2NO(g) + O2(g) → 2NO2(g)
Day

62. Question of the Day: Day 4 2-26 1. NaCl(s) + 3.88kJ  NaCl(aq)
Is this reaction endo OR exo?
Draw an enthalpy diagram representing the change above:
2. If 32.6 kJ of heat are given off, how many grams of calcium hydroxide are produced?
CaO(s) + H2O(l) → Ca(OH)2(s) kJ
3. Use your standard values handout to determine the standard entropy change for the formation of nitrogen dioxide shown in the rxn below. THEN explain whether your calculation makes sense using what you know about predicting changes in entropy!
2NO(g) + O2(g) → 2NO2(g)
Day