Ch 18 Free Energy And Thermodynamics

Question 1

What is the first law of thermodynamics? Give an example.

Answer 1

Energy can not be created or destroyed.

The total energy of combustion equals the energy that goes to propel the car and the amount dissipated as heat.

Question 2

Explain the Energy Tax

Answer 2

Every energy transition results in a loss of energy because of the conversion of energy to heat, which is lost by heating up the surroundings.

To recharge a battery with 100kJ of useful energy will require more than 100kJ because of the second law of thermodynamics.

Question 3

Thermodynamics predicts what?

Answer 3

Whether a process will occur under the given conditions.

Question 4

Explain Spontaneous vs Thermodynamically Favorble .

Answer 4

1) Processes that occur without ongoing outside intervention is called Spontaneous.
2) When the system has a after reaction has less potential energy that before the reaction.

Question 5

In general, entropy increase (🔺S > 0) for which 4 situations?

Answer 5

1) Phase transition from solid to liquid
2) Phase transition from solid to gas
3) Phase transition from liquid to gas
4) An increase in the number of miles of gas during a chemical reaction.

Question 6

Label the following reactions as endothermic or exothermic:

1) Melting
2) Vaporization
3) Freezing
4) Condensation

Answer 6

1) Melting - Endothermic
2) Vaporization - Endothermic
3) Freezing - Exothermic
4) Condensation - Exothermic

Question 7

The 2nd Law of Thermodynamics states what?

Answer 7

States that for any spontaneous process, the entropy of the universe increases. (🔺S univ > 0)

Question 8

An exothermic reaction is a process that ______🔺Hsys and a

_____🔺Ssurr?

Answer 8

An exothermic reaction is a process that has a negative 🔺Hsys and a positive 🔺Ssurr

Question 9

What is the relationship of 🔺G to 🔺Suniv at constant T and P?

Answer 9

🔺G is proportional to -🔺Suniv

Question 10

Consider a reaction that has a positive 🔺H and a negative 🔺S. What must be true about this reaction?

Answer 10

This reaction will be Non-spontaneous at all temperatures.

Question 11

If K is positive, what must be true about 🔺Grxn?

Answer 11

🔺Grxn is negative and the reaction is spontaneous in the forward reaction.

Question 12

What are the characteristics of Gibbs Free Energy at constant temperature and pressure?

Answer 12

1) 🔺G is proportional to the negative of 🔺S univ
2) A decrease in Gibbs Free Energy (🔺G < 0) corresponds to a spontaneous process.
3) An increase in Gibbs Free Energy (🔺G > 0) corresponds to a non spontaneous process.

Question 13

What are the characteristics of the Reversibility of Process?

Answer 13

1) If a process is spontaneous in one direction, it must be non-spontaneous in the opposite direction.
2) Any spontaneous process is irreversible because there is a net release of energy when it proceeds in that direction.
3) A reversible process is at equilibrium and results in no change in free energy.

Question 14

Why does graphite convert to diamond spontaneously and and not the other way around?

Answer 14

Graphite is more stable than diamond, so the conversion of diamond into graphite is spontaneous, but it is an incredibly slow process.

Question 15

T/F - Most spontaneous processes are exothermic.

Answer 15

True - But there are a few spontaneous processes that are endothermic. i.e. melting and vaporization.

Question 16

Define Entropy?

Answer 16

Entropy is a thermodynamic function that increases the number of energetically equivalent ways of arranging the components increases, represented by “S”.

Question 17

What is the equation for Entropy?

Answer 17

S = k ln W
k = Boltsman constant = 1.38 x 10 ^-23 J/K
W = The number of energetically equivalent ways a system can exist.

Question 18

How is the value of Entropy affected based on the state of existence the substance is in?

Answer 18

The value of Entropy more in gas over liquid and more in liquid over solid. Ssolid

Question 19

Which of the following reaction increases Entropy? Why?

1) CH4(g) + H2O(g)–>CO(g)+H2(g)
2) 2NH3(G)+CO2(G)–>NH2CONH2(aq)+H2O(l)
3) N2(g)+3H2(g)–>2NH3(g)

Answer 19

1) CH4(g) + H2O(g)–>CO(g)+H2(g) - Increases entropy because reaction goes from 2 molecules to 4.
2) 2NH3(G)+CO2(G)–>NH2CONH2(aq)+H2O(l) - decreases entropy because reaction goes from gas to liquid.
3) N2(g)+3H2(g)–>2NH3(g) - decreases entropy because reaction goes from 4 to 2 molecules.

Question 20

What are the characteristics of Heat Exchange and 🔺Ssurr?

Answer 20

1) An exothermic system adds heat to the surroundings and increases the entropy of the surrounds.
2) An endothermic system takes heat from the surroundings and decreases the entropy of the surroundings.
3) The amount of entropy changes of the surroundings depends on its original temperature.
4) There is greater impact on entropy when heat is added to surroundings at lower temperatures.