Lecture 2.pdf

# 20 mol so 2 l and 20 mol so 2 g 10 mol ch 4 g and 10

• Notes
• 19

This preview shows page 10 - 14 out of 19 pages.

2.0 mol SO 2( l ) and 2.0 mol SO 2( g ) 1.0 mol CH 4( g ) and 1.0 mol C 2 H 6( g ) 1.0 mol CH 4( g ) at 298 K and 1.0 mol CH 4( g ) at 273 K 1.5 mol Ar in 5.0 L and 1.5 mol Ar in 10.0 L 18 Reaction Entropy Standard reaction entropies ( Δ S ) Sign of reaction entropies ( Δ S ) Predict based on moles of gases Calculating standard reaction entropies ( Δ S o ) Δ S o = Σ nS m o P ( ) − Σ nS m o R ( ) Example 8 Calculating standard reaction entropy for N 2 H 4( l ) + 3 O 2( g ) 2 NO 2( g ) + 2 H 2 O ( l ) given the following standard molar entropies. S m o (H 2 O ( l ) ) = 69.91 J K –1 mol –1 S m o (N 2 H 4( l ) ) = 121.21 J K –1 mol –1 S m o (NO 2( g ) ) = 239.95 J K –1 mol –1 S m o (O 2( g ) ) = 205.03 J K –1 mol –1 19

Subscribe to view the full document.

Reaction Entropy Problem 5 How much entropy change accompanies the combustion of 0.454 mol of propane (C 3 H 8 )? S m o (C 3 H 8( g ) ) = 270.3 J K –1 mol –1 S m o (CO 2( g ) ) = 213.8 J K –1 mol –1 S m o (H 2 O ( l ) ) = 69.91 J K –1 mol –1 S m o (O 2( g ) ) = 205.03 J K –1 mol –1 20 Global Changes in Entropy Entropy change of surroundings Process spontaneous if overall entropy change positive Δ S tot = Δ S + Δ S surr Δ S surr = q surr T Δ S surr = Δ H T 21
Global Changes in Entropy Overall change in entropy Entropy change and spontaneity Δ S tot > 0 Spontaneous Δ S tot < 0 Reverse process spontaneous Δ S tot = 0 Not spontaneous in either direction 22 Δ S > 0 Δ S < 0 Exothermic Δ S surr ___ 0 Endothermic Δ S surr ___ 0 Global Changes in Entropy Overall change in entropy Entropy change and spontaneity 1. Determine type of system If isolated If open or closed 2. Calculate the entropy change for system 3. If necessary calculate the entropy change for the surrounding 4. If necessary, calculate the total entropy change 5. Use the sign of Δ S tot (or Δ S ) to determine spontaneity Spontaneous when Δ S tot (or Δ S ) _____ 0 23

Subscribe to view the full document.

Global Changes in Entropy Overall change in entropy Entropy change and spontaneity Example 9 Is the reversible expansion of 0.755 mol of an ideal gas at room temp from 6.60 L to 8.05 L spontaneous? R is 8.314 J K –1 mol –1 . Explain briefly. 24 Global Changes in Entropy Problem 6 Is the expansion of 0.755 mol of an ideal gas at room temp from 6.60 L to 8.05 L at 1.50 atm spontaneous? Explain briefly. R is 8.314 J K –1 mol –1 and 1 L atm = 101.325 J. 25
Global Changes in Entropy Problem 7 When 250. g copper block at 50 o C is placed next to 12.0 g (0.666 mol) ice cube at 0 o C, will the system spontaneously reach 5 o C? Explain briefly. Assume no heat loss. The heat capacities of copper, water and ice are 0.38 J o C –1 g –1 , 4.184 J o C –1 g –1 and 2.03 J o C –1 g –1 respectively. The heat of fusion of water is 6.01 kJ mol –1 .
You've reached the end of this preview.
• Winter '01
• Lavelle

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern