Chapter 17 Flashcards

Vocabulary flashcards for Chapter 17: Entropy, Gibbs Energy, and Equilibrium.

First Law of Thermodynamics

Energy cannot be created or destroyed; the total energy of the universe remains constant, but can transfer from one place to another.

Spontaneous Process

A process that occurs under given conditions, determined by comparing the free energy of the system before and after the reaction.

Thermodynamically Favorable

A reaction where the system after reaction has less free energy than before the reaction.

Enthalpy (ΔH)

The comparison of the bond energy of reactants to products. A negative ΔH indicates an exothermic reaction, while a positive ΔH indicates an endothermic reaction.

Exothermic Reaction

A reaction that releases energy, resulting in a negative ΔH and more stable products than reactants.

Endothermic Reaction

A reaction that absorbs energy, resulting in a positive ΔH and less stable products than reactants.

Entropy (S)

A thermodynamic function that measures the randomness/disorderliness of a system; it increases as the number of energetically equivalent ways of arranging the components increases.

Boltzmann Constant (k)

A constant is equal to 1.38 x 10-23 J/K, used in the entropy equation S = k lnW.

Microstates (W)

The number of energetically equivalent ways of arranging the components of a system; used in the entropy equation S = k lnW.

Entropy Change (ΔS)

A measure of the change in randomness/disorderliness of a system. Positive ΔS indicates an increase in entropy (more disorder).

Second Law of Thermodynamics

The total entropy change of the universe must be positive for a process to be spontaneous; ΔSuniverse = ΔSsystem + ΔSsurroundings must be positive.

Reversible Process

A process where the entropy change of the universe is zero (ΔSuniverse = 0).

Irreversible Process

A spontaneous process where the entropy change of the universe is positive (ΔSuniverse > 0).

Gibbs Free Energy (G)

The maximum amount of energy from a system available to do work on the surroundings. G = H – T(S).

Spontaneous Reaction (ΔG)

Occurs when there is a decrease in free energy of the system that is released into the surroundings; therefore a process will be spontaneous when ΔG is negative.

Third Law of Thermodynamics

For a perfect crystal at absolute zero (0 K), the absolute entropy is zero. Every substance that is not a perfect crystal at absolute zero has some energy from entropy and therefore the absolute entropy of substances is always positive.

Standard Entropy (So)

Entropies for 1 mole at 298K for a particular state, a particular allotrope, particular molecular complexity, a particular molar mass, and a particular degree of dissolution.

ΔSsurroundings

Change in entropy of the surroundings. Equal to −Δ𝐻𝑠𝑦𝑠 / T

ΔGsys

The change in Gibbs Free Energy of a system. Equal to ΔHsys - T ΔSsys

ΔGo reaction

Change in Gibbs Free Energy under standard conditions. Equal to ∑nΔGo f(products) - ∑nΔGo f reactants

Relationship between ΔGo and K

ΔGo = -RTlnK, where K is the equilibrium constant, R is the gas constant, and T is the temperature in Kelvin.

Effect of Temperature on K (Exothermic)

For an exothermic reaction, increasing the temperature decreases the value of the equilibrium constant K.

Effect of Temperature on K (Endothermic)

For an endothermic reaction, increasing the temperature increases the value of the equilibrium constant K.

Nonspontaneous

A reaction is nonspontaneous when ΔG > 0.

Spontaneous

A reaction is spontaneous when ΔG < 0.

Equilibrium

A reaction is at equilibrium when ΔG = 0.

Bond Energy

Is the amount of energy needed to break a bond.

Positive ΔS

Indicates an increases in entropy. Reactions whose products are in a more disordered state (solid > liquid > gas), Reactions which have larger numbers of products molecules than reactant molecules, Solids dissociating into ions upon dissolving, or Increasing temperature.

Negative ΔS

For these cases, the entropy change is negative due to hydration of ions, which causes water molecules to become ordered around ions.

ΔG = ΔGo + RTlnQ

Gibbs Free Energy equation under nonstandard conditions.

ΔG = 0

At equilibrium

ΔGo = -RTlnK

Gibbs Free Energy at standard conditions where K is the equilibrium constant.

G = H – T(S)

Equation for Gibbs Free Energy.

molecular complexity

For different substances in the same phase, this factore determines which ones have higher entropies.

Macrostate

A possible arrangement of particles

Standard Entropy Values

Includes molar mass, Allotropes, Molecular Complexity, and Dissolution

Molecular Complexity

Larger, more complex molecules generally have larger standard entropy values

Allotropes

The less constrained the structure of this group is, the larger the entropy

ΔEuniverse = 0

ΔEsystem + ΔEsurroundings

Temperature Dep. of ΔSsurroundings

As temperature increases, a given negative enthalpy produces a smaller positive ΔSsurroundings