Thermochemistry, Thermodynamics, Solutions, and Kinetics Review

Flashcards covering key vocabulary and concepts from Units 1 (Thermochemistry and Thermodynamics), 2 (Solutions), and 3 (Kinetics).

Potential energy

Energy associated with the position or composition of an object.

Kinetic energy

Energy associated with the motion of an object.

Thermal energy

Energy associated with the temperature of an object.

Chemical energy

Energy associated with the relative positions of electrons and nuclei in atoms and molecules.

Conservation of energy

The law stating that energy cannot be created or destroyed.

System doing work on surroundings and gaining heat

q = +, w = -

System losing heat to surroundings and having work done on it

q = -, w = +

System gaining heat and having work done on it

q = +, w = +

System losing heat and doing work on surroundings

q = -, w = -

Entropy

A thermodynamic function that increases with the number of energetically equivalent ways to arrange components of a system to achieve a particular state.

First Law of Thermodynamics

States that energy cannot be created or destroyed.

Second Law of Thermodynamics

States that for any spontaneous reaction, the entropy of the universe increases.

Third Law of Thermodynamics

States that the entropy of a perfect crystal at absolute zero (0 K) is zero.

Entropy change (ΔS) for phase transitions

ΔS decreases (ΔS < 0) for freezing (l → s), condensation (g → l), and gas reacting to form fewer moles of gas. ΔS increases (ΔS > 0) for melting (s → l), boiling (l → g), and gas reacting to form more moles of gas.

Entropy order for a given compound

Gas > Liquid > Solid (decreasing order of entropy).

Solution formation condition

A solution will form between two substances if the solute-solvent interactions are of comparable strength to the solute-solute and solvent-solvent interactions.

Major force between ethanol and water

Hydrogen bonding.

Major force in seawater

Ion-dipole forces.

Major force between acetone and chloroform

Dipole-dipole forces.

Endothermic ΔHsolution

Occurs when |ΔHsolute| > |ΔHhydration|, meaning more energy is required to separate solute particles than is released when they are hydrated.

Unsaturated solution

A solution containing less than the equilibrium amount of solute.

Supersaturated solution

A solution containing more than the equilibrium amount of solute.

Solubility of a solid

Is highly dependent on temperature but not significantly on pressure.

Purification of a solid technique

Crystallization (or recrystallization).

Colligative properties

Properties that depend on the number of solute particles in a solution, not on their identity. Examples include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

Purpose of road salt in wintertime

To lower the freezing point of water (freezing point depression), causing ice to melt at lower temperatures.

Rate of reaction (with respect to a reactant/product)

The change in concentration of a reactant or product per unit time, often adjusted for stoichiometric coefficients.

First-order reaction (one reactant)

The rate of the reaction is directly proportional to the concentration of the reactant (Rate = k[A]).

Zero-order reaction (one reactant)

The rate of the reaction is independent of the concentration of the reactant (Rate = k).

Second-order reaction (one reactant)

The rate of the reaction is proportional to the square of the concentration of the reactant (Rate = k[A]^2).

Overall reaction order

The sum of the exponents of the concentration terms in the rate law. For Rate = k[NO][O3], the overall order is 1+1=2.

Rate constant (k) and temperature

Typically increases with an increase in temperature, leading to a faster reaction rate.

Rate-determining step

The slowest step in a reaction mechanism, which limits the overall rate of the reaction.

Reaction rate dependency (Rate = k[X][Y]^2) if [Y] is doubled

The rate of reaction will increase by a factor of four (2^2).

Bimolecular reaction

A reaction step in a mechanism involving the collision of two reactant species. Examples: Rate = k[A][B] or Rate = k[A]^2.

Enzymes (function)

Biological catalysts that increase the rate of biochemical reactions by lowering the activation energy without being consumed in the process.