Thermodynamics Flashcard

 

 

 

 

Second Law of Thermodynamics

 

 

 

For any spontaneous process, the entropy of the universe increases (◊Suniv>0) 

 

 

 

 

 

 

 

 

Entropy increases (◊S>0) for each of the following:

 

 

The phase transition from a solid to a liquid

The phase transition from a solid to a gas

The phase transition from a liquid to a gas

An increase in the number of moles of a gas during a chemical reaction

 

 

 

 

Entropy of the universe, system, and surroundings

◊Suniv= ◊Ssys + ◊Ssurr

 

The entropy of the universe must increase (&loz;Suniv>0) for a process to be spontaneous. The entropy of the system could therefore decrease (&loz;Ssys<0) as long as the entropy of the surroundings increases by a greater amound (&loz;Ssurr> -&loz;Ssys)

 

 

 

&loz;Ssurr = -&loz;Hsys

                  T

(at constant T and P)

 

 

&loz;Ssurr = -&loz;Hsys

                   T

(at constant T and P)

 

 

 

 

&loz;G = &loz;H – T&loz;S

 

 

 

 

 

&loz;G = &loz;H – T&loz;S

 

 

 

 

Gibbs Free Energy

 

 

 

A decrease in Gibbs free energy (&loz;G < 0) corresponds to a spontaneous process

 

An increase in Gibbs free energy (&loz;G > 0) corresponds to a nonspontaneous process

 

 

 

 

When &loz;H is negative and &loz;S is positive, is the reaction spontaneous or nonspontaneous?

 

 

 

 

It is spontaneous at all temperatures

 

 

 

 

 

When &loz;H is positive and &loz;S is negative, is the reaction spontaneous or nonspontaneous?

 

 

 

 

 

It is nonspontaneous at all temperatures

 

 

 

 

When &loz;H and &loz;S are both negative, is the reaction spontaneous or nonspontaneous?

 

 

 

 

 

 

It is spontaneous at low temperatures, but nonspontaneous at high temperatures.

 

 

 

 

When &loz;H and &loz;S are both positive, is the reaction spontaneous or nonspontaneous?

 

 

 

 

 

It is nonspontaneous at low temperatures, and spontaneous at high temperatures.

 

 

 

 

The standard state of a substance is defined as follows:

For a gas: The standard state for a gas is the pure gas at a pressure of exactly 1 atm.

For a liquid or solid: The standard state for a liquid or solid is the pure substance in its most stable form at a pressure of 1 atm and the temperature of interest (often taken to be 25 C)

For a Substance in Solution: The standard state for a substance in solution is a concentration of exactly 1M.

 

 

 

 

Entopies of gases, liquids, and solids:

 

 

 

 

The entropy of a gas is generally greater than a liquid, which is in turn greater than the entropy of a solid.

gas>liquid>solid

 

 

 

Entopies related to molar mass:

 

 

 

 

Entropy increases with increasing molar mass.

 

 

 

 

Entropies related to molar complexity:

 

 

 

 

 

Entropy generally increases with increasing molar complexity

 

 

 

 

 

 

 

Entropies related to dissolution:

 

 

 

 

The dissolution of a crystalline solid into solution usually results in an increase in entropy.

 

 

 

Determining &loz;G°rxn for a stepwise reaction from the changes in free energy for each of the steps

If a chemical equation is multiplied by some factor, then &loz;Grxn is also multiplied by the same factor

If a chemical equation is reversed, then &loz;Grxn changes sign

If a chemical equation can be expressed as the sum of a series of steps, then &loz;Grxn for the overall equation is the sum of the free energies of reactions for each step.

 

 

 

 

 

 

The free energy change of a reaction under nonstandard conditions (&loz;Grxn)

 

 

 

&loz;Grxn = &loz;G&deg;rxn + RTlnQ

 

 

 

 

 

&loz;G&deg;rxn = -RTlnK

 

 

 

 

&loz;G&deg;rxn = -RTlnK

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