SI Chem 178
Ch 19 (Thermo)
Leader: Emily
Session Date: 4/4/2013
Concepts:
Do thermodynamics tell us about rate? If not, what does?
Spontaneity-
To reverse a spontaneous process, you may have to add ______to the system, this helps to prove that it is REVERSIBLE or IRREVERSIBLE.
Spontaneous processes occur in ONE / BOTH direction(s).
Entropy is + or – with spontaneous processes.
T/ F Spontaneity can be conditional (ex: based on surrounding temp.) Can you give an example that supports your answer?
Reversibility-
The S of a reversible process is______.
YES or NO: Reversible processes are commonly observed in the real world. (Consider what is always increasing in the universe and the entropy of a reversible process.)
Entropy-
Definition: Measures ______in a system.
With the above definition in mind, what do + / - signs represent for entropy. Give examples of each.
Isothermal means that T = ______. It can also be said that an isothermal system is staying at a ______temperature.
What are two isothermal processes discussed in class?
What equation helps us quantify the entropy associated with these processes? How do we use this equation?
What are three types of molecular movement we can observe on a molecular level? Which of these can be observed in ice?
When assessing a problem or examples, what are things that can give you clues about the sign (+ / -) of your entropy value? In other words, what increases/decreases entropy?
What is the entropy at absolute zero? Why?
19.4 Concepts (Consult your book, pages 802-803 for help with these concepts!!)
What are the units for entropy? ______
What is the equation for entropy change in a chemical reaction? What do “m” and “n” represent?
T / F Standard entropies for chemicals are dependent on pressure and temperature.
Standard entropies of gases are OR < liquids and gases.
As molar mass increases, standard entropies ______. Why? Consider methane and ethane.
The above equation quantifies entropy for a system OR surroundings?
The entropy change in surroundings during an isothermal process is the opposite as that for a system. How would you write this? (It’s simpler than you might think… consider signs)
In a constant pressure process, qsys can be quantified using ENTHALPY (total energy of a system). Then, this can later be used to give us information about ENTROPY as related to surroundings.
How can we express enthalpy in arxn? What does the sign of an enthalpy calculation tell us?
Now, you can use this calculated value of ENTHALPY (H) to determine your ENTROPY of your surroundings.
Finally, this can be used to quantify S universe. What is the equation for that? (it was presented today!)
Problems (Quiz Prep):
14.115 (See problem 14.116 for further practice on this topic!)
Given the following information, what is the S for the following reactions:
Both are from p. 802 in the text
N2(g) + 3H2(g) 2NH3(g) (Standard entropies (J/mol K) are 191.5, 130.6, and 192.5 respectively)
Al2O3(s) + 3H2(g) 2Al(s) + 3H2O(g) (51.00, 130.58, 28.32, 188.83)
I want to freeze 46g of water, what is our S for this? Which equation do we use?
(MW = 18g/mol, Hf= 6.01 KJ/mol)
Review Ea diagrams. (See Doc Cam)