SLIDE 1
Entropy, continued UNIT 4 Day 7 Demonstration Stretched vs. - - PowerPoint PPT Presentation
Entropy, continued UNIT 4 Day 7 Demonstration Stretched vs. - - PowerPoint PPT Presentation
Sparks CH301 The 2 nd Law of Thermodynamics Entropy, continued UNIT 4 Day 7 Demonstration Stretched vs. Relaxed Rubber Bands POLL: iClicker Question For the process of releasing a stretched rubber band to a relaxed rubber band, S sys is
SLIDE 2
SLIDE 3
POLL: iClicker Question
For the process of releasing a stretched rubber band to a relaxed rubber band, ∆Ssys is A.> 0
- B. = 0
- C. < 0
D.No way to know
SLIDE 4
What affects the entropy of the system? Volume Change Mixing Phase Change Temperature Change Chemistry
Entropy
SLIDE 5
Entropy and Temperature
SLIDE 6
Entropy and Temperature
SLIDE 7
During a phase change, the heat is the reversible heat and the temperature is constant
Entropy for a Phase Change
SLIDE 8
Reactants Products
Entropy for a Chemical Change
During a chemical change, the heat is NOT the reversible heat and the temperature is constant We need to be able to find the entropy of a substance
SLIDE 9
The entropies of all perfect crystals approach zero when the absolute temperature approaches zero. Now that we’ve defined zero entropy, we can establish other entropy values using it as a basis. We can use entropy change from temperature change and phase change to find the entropy of any substance at any temperature
The Third Law of Thermodynamics
SLIDE 10
Zero K Above zero K; below MP
SLIDE 11
Poll: Clicker Question
- Does S° for an element in its standard state at
1 atm and 298K have a value of zero?
- A. Yes
- B. No
11
SLIDE 12
Standard Molar Entropies (Absolute Entropies)
- The standard molar entropies (S⁰) increase as
the complexity of a substance increases.
12
SLIDE 13
2H2(g) + O2(g) 2H2O(l)
Absolute Entropies
NOTE: This is not the same as enthalpy of formation. All elements in their standard states have values
SLIDE 14
What affects the entropy of the system? Volume Change - only qualitative Mixing - only qualitative Phase Change Temperature Change Chemistry
Entropy
ΔS = q/T What is q for a phase change?
SLIDE 15
- Determine if the change of entropy is negative or positive
without calculating the change in entropy
- 1. H2O (s) H2O (l)
- 2. H2O (g) H2O (l)
- 3. PCl3 (g) + Cl2 (g) PCl5 (g)
- 4. 2 N2O5 (g) 4 NO2 (g) + O2 (g)
- 5. MgSO4• 7H2O (s) MgSO4 (s) + 7 H2O (g)
- 6. HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)
15
SLIDE 16
Calculate ΔSuniverse after the completion of the following reaction: 2NiS(s) + 3O2(g) → 2SO2(g) + 2NiO(s) at 25 °C ΔH = -890 kJ Substance S(J/Kmole) SO2 248 NiO 38 O2 205 NiS 53
16
SLIDE 17
What have we learned today?
- Entropy changes for chemical and physical
processes – qualitative and quantitative determinations.
SLIDE 18