Chapter 19 Lecture Worksheet
Homework:19.29, 19.31, 19.37, 19.39, 19.41, 19.43, 19.47, 19.51, 19.53a, 19.55, 19.61, 19.73, 19.75, 19.77
Recall from Chapter 5
- 1st Law of Thermodynamics
o Energy is neither ____________________________________________. o Energy of the universe is constant.
o Enthalpy Change
▪ Heat energy transferred at _____________________________________ ▪ Negative value =
▪ Positive value =
o Tells us the _______________________________________ of a reaction ▪ Is the reaction ________________________? o Does NOT tell us the ________________ at which it happens. - Spontaneous change
o One that proceeds to _________________ without outside ________________________ o If a reaction is ____________________ in one direction, it is _________________________ in the reverse direction. o ________________ will affect spontaneity
- _____________________ reactions are typically thought to be _____________________. o Not always the case though!
o Something else must be occurring
Entropy and the Second Law of Thermodynamics
o Symbol: S
o Randomness or Disorder
- Change in Entropy
o Depends only on the initial and final values [state function]. o Symbol:ΔS = Sfinal – Sinitial
- Second Law of Thermodynamics
o The total entropy of the universe increases in any spontaneous process. o ΔSuniverse = ΔSsystem + ΔSsurroundings ▪ If ΔSuniverse is positive, then process is _____________________________ ▪ If ΔSuniverse is negative, then process _____________________________________ as written. ▪ ΔSuniverse is zero, then system is at _________________________. - How do you calculate ΔSuniverse?
o ΔSsystem =
▪ Values in the back of the book.
o What about ΔSsurroundings?
▪ ΔSsurr =
The Molecular Interpretation of Entropy
- If ΔS is positive, entropy increases
o More entropy = _________________ = ________________________ - If ΔS is negative, entropy decreases
o Less entropy = __________________ = ________________________ - Processes that change entropy
o ___________________ formed from a solid.
o ______________ formed from liquid or solid.
o ______________________ increase
o _________________ increases
Practice Problem 19.1Predict the sign of ΔS of the following reactions. a. CaCO3(s) → CaO(S) + CO2(g)
b. CS2(l) → CS2(g)
c. 2Hg(l) + O2(g) → 2HgO(s)
d. 2Na2O2(s) + 2H2O(l) → 4NaOH(aq) + O2(g)
- Third Law of Thermodynamics
o Establishes that ________________ in a perfect crystal at 0 K. o All substances have ______________________________values above 0 K Entropy Changes in Chemical Reactions
- Can determine the absolute entropy of a substance
- Based on reference point of zero entropy for a perfect crystalline solid at 0 K [third law] - Standard molar entropies
o Molar entropy values in their standard states
o NOT ________________ for elements [remember that H° is!] o
o Increase with increasing _______________________ o Increase with increasing _______________________ Practice Problem 19.2Predict which substance has the higher entropy and explain your reasoning. Look up the values and see how they actually compare. a. Oxygen or ozone
b. SnCl4(l) or SnCl4(g)
- Entropy changes for physical and...