Unit 9 Review

AP Unit 9 Review

Applications of Thermodynamics

Entropy (disorder) increases when:

• the number of gas molecules increases from reactants to products

• a solution is formed

• temperature (average KE) increases

• pressure is decreased

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​9.1 Entropy

​9.2 Entropy Change

• An process which results in an increase in entropy has a positive ▲S.

  • combustion or boiling

• An process which results in an decrease in entropy has a negative ▲S.

  • precipitation

Multiple Select

Which of the following has an increase in entropy and a ▲S>0? (check all)

• $$NaCl\left(aq\right)\rightarrow Na^+\left(aq\right)+Cl^-\left(aq\right)$$

• $$Ag^+\left(aq\right)+Br^-\left(aq\right)\rightarrow AgBr\left(s\right)$$

• $$2SO_3\left(g\right)\rightarrow2SO_2\left(g\right)+O_2\left(g\right)$$

• $$H_2O\left(l\right)\rightarrow H_2O\left(s\right)$$

Math Response

Given the following absolute entropies:

N₂(g)                S°=192J/molK

O₂(g)                S°=205J/molK

NO                  S°=211J/molK

What is the change in entropy,▲S°, for the following reaction? 

N₂(g)+O₂(g)→2NO

Type answer here

Correct Answer: 25

Deg^°

Rad

Gibb's Free Energy

• Used to predict favorability of a reaction.

• ▲G > 0 - non spontaneous, reactants favored

• ▲G < 0 - spontaneous, products favored

• ▲G = 0 - equilibrium

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​9.3 Gibb's Free Energy and Favorability

▲G = ▲H - T▲S

Remember: ▲H is usually in kJ/mol and ▲S is in J/molK, so converting might be needed.

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​9.3 cont'd

​▲H	▲S​	​T	​▲G	​Spontaneous
​-	+​	All​	-​	​Always
-​	-​	​Low	-​	​Yes
-​	-​	High​	​+	​No
+​	+​	Low​	​+	No​
+​	+​	High​	​-	​Yes
+​	-​	All​	​+	Never​

Multiple Select

Which of the following would have a negative ▲G and would have products favored?

• ▲H<0

  ▲S<0

  high T

• ▲H>0

  ▲S>0

  high T

• ▲H<0

  ▲S>0

  low T

• ▲H>0

  ▲S<0

  low T

Math Response

Calculate the standard free-energy change (ΔG°) at 25°C for the reaction to the nearest whole #:

H₂(g)+O₂(g)⇌H₂O₂(l)

At 25°C, the standard enthalpy change (ΔH°) is −189 kJ/mol, and the absolute entropies of the products and reactants are:

S°(H₂O₂) = 110 J/(mol•K),

S°(O₂) = 205 J/(mol•K), and

S°(H₂) = 131 J/(mol•K).

Type answer here

Correct Answer: -122

Deg^°

Rad

Entropy increases when:

• the number of

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​9.4 Thermodynamic and Kinetic Control

Entropy increases when:

• the number of

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​9.5 Free Energy and Equilibrium

Entropy increases when:

• the number of

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​9.6 Coupled Reactions

Entropy increases when:

• the number of

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​9.7 Voltaic and Electrolytic Cells

Entropy increases when:

• the number of

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​9.8 E_cell and Free Energy

Entropy increases when:

• the number of

• adfa

• afsd

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​9.9 Non Standard Cells