salt/ Ammonia Barium Hydroxide demo
Did this reaction occur spontaneously? Is the reaction exothermic or endothermic?
NH4Cl + Ba(OH)2 .8H2O 10H2O
BaCl2 + 2NH3 +
Entropy: Disorder/ Chaos Entropy increasing
is a spontaneous process Molecules tend to move spontaneously to a state of maximum randomness 2nd law of Thermodynamics: Entropy of universe
Symbol S
Sign convention S+ when randomness increases Sign convention Swhen randomness decreases
Which of the following are spontaneous In all spontaneous A) Heat flow from processes? a cold object to a hot
object processes randomness B) Diffusion of perfume molecules from is increasing one side of the room to the other C) Decomposition of rust (Fe2O3.H2O) to iron metal, oxygen, and water D) Burning wood E) A ball rolling down a hill
Effect of phase on Entropy
Predict the sign of S in the system for each of the following:(g) (sublimation of dry ice) a) CO2(s) CO2
b) CaSO4 (s) d) I2 (s) CaO (s) + SO3 (g) 2NH3 (g) c) N2 (g) + 3H2 (g) I2 (aq) (dissolution of I2 in water)
Probability
Why is disorder easier to achieve than order?
If I have 20 coins, what is the probability that all will be heads when I flip them?
How does entropy change for this situation? How would entropy change as a molecule goes from solid to liquid to gas?
Summary
There are two things which dictate whether a process occurs spontaneously
1) The enthalpy of the reaction (whether the reaction is exothermic or endothermic) DH 2) The entropy of the reaction: degree of disorder DH Why did the reaction between the ammonia salt and barium hydroxide proceed? What evidence do you have for this?
Entropy and Temperature
What happens to molecular motion as a substance is heated? As motion increases, randomness will increase Under conditions of constant temperature and pressure:
Ssurr = -H or Ssys = H T T sign convention:
Rubber Band Demonstration
Free Energy
What are the two processes that dictate whether a reaction is spontaneous?
G = H - TS
Effect of Gibbs Free Energy on Entropy and Enthalpy Changes
Example:
The enthalpy of fusion of NH3 is and 5.65kJ/mol the entropy of fusion is 28.9J/K.mol. A) Will NH3spontaneously melt at 200K? B) What is the approximate melting point of NH3?
State Functions
Gibbs Free Energy, Entropy, and Enthalpy are all state functions What is a state function? A state which is independent of the path taken to get there. Is temperature a state function? Is work a state function?
Calculating G for reactions
Standard state of formation Gfo = change in free energy that accompanies the formation of 1 mole of that substance from its constituent elements with all the reactants and products in their standard state (298K, 1 atm pressure).
Example
Consider the reaction: Fe2O3 (s) + 3H2 2Fe(s) + 3H2O(g) Use Gfo values in appendix C to calculate Go for this reaction. Is this reaction spontaneous? The H for this reaction is 100kJ. At what temp. is the reaction spontaneous? (Assume H and S do not depend upon temperature.)
Example 2
You are a chemical engineer. Your plant wants to start making acetic acid. Which way is a better way (thermodynamically speaking) to produce acetic acid? Why? Use appendix C (p.1112 in 11th edition). CH4 (g) + CO2 (g) CH3COOH (l) OR CH3OH (g) + CO (g) CH3COOH (l)
rd 3
Law of Thermodynamics
Entropy of a pure crystalline substance at absolute zero ...