Ch 19: Free Energy and Thermodynamics

Question 1

The criterion for spontaneity in chemical systems must be entropy. The concept of disorder or randomness is analogous to entropy.
The formal definition of entropy is “a thermodynamic function that increases with the number of __________ __________ ways to arrange the components of a system to achieve a particular state.

Answer 1

energetically equivalent

Question 2

What is Boltzmann’s equation?

Answer 2

S = k ln W

S represents entropy.

k is the Boltzmann constant, which is the gas constant, R, divided by Avogadro’s number: R/N_A = 1.38 x 10^-23 J/K

W is the number of energetically equivalent ways to arrange the components of a system.

Question 3

A state in which a given amount of energy is more highly _________ (or more highly randomized) has more entropy than a state in which the same energy is more highly concentrated.

Answer 3

dispersed

Question 4

State the 2nd law of thermodynamics.

Answer 4

For any spontaneous process, the entropy of the universe increases (ΔS_universe > 0).

Question 5

Processes that decrease the entropy of the universe do not _____ _____________.

Answer 5

occur spontaneously

Question 6

The larger and more complex the molecule the (smaller/larger) the entropy.

Answer 6

larger

Question 7

A solution containing AgNO₃ is mixed with a solution of NaCl to form a solution that is 0.10 M in AgNO₃ and 0.075 M in NaCl. What will happen once these solutions are mixed? K_sp (AgCl) = 1.77 × 10^-10.

Since Q > K_sp, what do you expect will happen?

Answer 7

Silver chloride will precipitate out of solution, leaving a saturated AgCl solution.

Question 8

Reactions in which the entropy of the universe increases occur __________, where as reactions that decrease the entropy to the universe are _____________.

Answer 8

spontaneous

nonspontaneous

Question 9

When ΔH and ΔS are both negative, the reaction is ___________ at all temperatures below T_eq. For a reaction in which ΔH and ΔS are both positive, the reaction is spontaneous at all temperatures above T_eq.

Answer 9

spontaneous

Question 10

The spontaneity of a reaction can be determined solely from the sign of ΔG, where a negative value (release of energy) indicates that the reaction is ___________, and a positive value indicates that it is nonspontaneous (requiring energy to occur).

Answer 10

spontaneous

Question 11

What formula is needed to calculate the ΔG_rxn under nonstandard conditions?

Answer 11

ΔG_rxn = ΔG°_rxn + RT ln Q

Question 12

For the reaction below, what can you conclude about ΔG°_rxn for the reaction?

H₂(g) + Br₂(g) ⇄ 2 HBr(g) K = 2 × 10¹⁹ (at 25°C)

Answer 12

Since K is much larger than 1, we know that ΔG°_rxn < 0.

it’s a strongly product-favored reaction.

Question 13

What formula(s) do you need to calculate the ΔS_universe?

Answer 13

ΔS_universe = ΔS_system + ΔS_surroundings

ΔS_surroundings = -ΔH_sys/T