IB Chemistry - Thermodynamics and Equilibrium

Flashcards on Thermodynamics and Equilibrium based on lecture notes.

Spontaneous Process

Occurs without outside intervention; refers to the increase in microstates; may be fast or slow.

Entropy (S)

A measure of randomness or disorder, or increase in microstates; associated with probability (more ways for something to be disorganized than organized).

Entropy and States of Matter

Entropy increases going from a solid to a liquid to a gas.

Entropy and Solutions

Entropy increases when solutions are formed.

Entropy and Reactions

Entropy increases in reactions when more atoms or molecules are formed.

Entropy and Temperature

Entropy increases with increasing temperature.

2nd Law of Thermodynamics

In any spontaneous process, there is always an increase in the entropy of the universe. The energy of the universe is constant, but the entropy of the universe is increasing.

Third Law of Thermodynamics

Defines a perfect crystal at 0 K as having maximum order and an Entropy value of zero.

Unit for Entropy

Joules (J) - an energy term; the degree of disorder depends on movement (translation), vibration, and rotation, which all have a Kinetic Energy component and a Potential Energy component.

Calculating ΔS°

ΔS° = Σ S° products - Σ S° reactants; requires the use of the formula along with access to Standard Entropy values.

Gibb's Free Energy

Used to explain whether a physical or chemical process is thermodynamically favored based on an evaluation of ΔG°.

Free Energy (G)

ΔG = ΔH - TΔS; a measure of the spontaneity of a reaction; the maximum work available from the system.

Internal Energy Change (ΔU)

ΔU = Q - W; equal to the heat added to the system minus the work done by the system.

Exothermic Reaction and Entropy

Releases energy to the surroundings and causes the entropy of the surroundings to increase (ΔS = +ve).

Endothermic Reaction and Entropy

Takes in energy from the surroundings, and the entropy of the surroundings decreases (ΔS = -ve).

Spontaneous Reaction (Constant Temperature and Pressure)

Has a negative ΔG. For example, when ice melts, ΔH is positive (endothermic), ΔS is positive, and ΔG = 0 at 0°C.

ΔG and Reaction Behavior

Negative ΔG: Proceeds spontaneously to the right; Zero ΔG: Is at equilibrium; Positive ΔG: Will not proceed.

Spontaneity and ΔH/ΔS Combinations

ΔS positive and ΔH negative = spontaneous at all temp; ΔS positive and ΔH positive = spontaneous at high temp; ΔS negative and ΔH negative = spontaneous at low temp; ΔS negative and ΔH positive = nonspontaneous.

ΔG Relationship

If ΔH and ΔS are both negative or positive, then ΔG has a variable sign.

Third Law of Thermodynamics

The entropy of a perfect crystal at 0 K is zero. ΔS° reaction = ΣS° prod - ΣS° react

Standard Free Energy Change (ΔG°)

Change in free energy that occurs if the reactants in their standard states are converted to products in their standard states. ΔG° = ΣΔGf° prod - Σ ΔGf° react at standard conditions. ΔGf° for a free element in its standard state is zero.

Gibbs-Helmholtz Equation

ΔG° = ΔH° - T ΔS° (When working this, change S to kJ and T has to be in Kelvin)

Free Energy and Reaction Quotient

ΔG = ΔG° + RT ln (Q); Q = reaction quotient (partial pressure of products/reactants raised to the power of their coefficients); T = temperature in Kelvin; R = gas constant 8.314 J/K mol; ΔG° = free energy change at 1 atm.

Equilibrium Point

Occurs at the lowest value of free energy available to the reaction system. ΔG = Gprod - Greact = 0

Equilibrium and Free Energy

At equilibrium, ΔG = 0

ΔG° and K

ΔG° = -RT ln K

Free Energy and Useful Work

Free energy is energy available to do useful work. Wmax = ΔG