Heat & Chemical Reactions Vocabulary

Vocabulary flashcards defining fundamental concepts in thermodynamics, Gibbs free energy, and standard enthalpy changes.

Universe

Everything that exists, possessing a total energy content that is constant and can neither be created nor destroyed.

System

The specific part of the universe under study or observation.

Surroundings

Everything outside the system but still considered part of the universe.

Boundary

The separating surface that divides the system from its surroundings.

Open System

A system that can exchange both mass and energy with its surroundings.

Closed System

A system that can exchange energy with its surroundings, but cannot exchange mass.

Isolated System

A system that exchanges neither mass nor energy with its surroundings.

Thermodynamics

The branch of science that studies the relationship between heat and other forms of energy.

Zeroth Law of Thermodynamics

States that if object $A$ is in thermal equilibrium with $B$ and $B$ is in thermal equilibrium with $C$, then $A$ and $C$ are in thermal equilibrium and share the same temperature.

First Law of Thermodynamics

States that energy can neither be created nor destroyed, only transformed from one form to another, represented by the formula $\to \Delta U = q + w$.

Second Law of Thermodynamics

States that the total entropy of an isolated system always increases over time.

Third Law of Thermodynamics

States that the entropy of a closed system at thermodynamic equilibrium approaches a constant value as temperature approaches absolute zero ($0\,K$).

Intensive Properties

Properties unaffected by a change in the amount of matter, such as boiling point, melting point, density, and specific heat capacity.

Extensive Properties

Properties affected by a change in the amount of matter, such as mass, volume, internal energy, heat capacity, and enthalpy change.

Gibbs Free Energy ($\Delta G$)

The useful energy available to perform work, which determines the fate or spontaneity of a chemical reaction.

Enthalpy Change ($\Delta H$)

The heat content of a reaction, representing the amount of heat absorbed or liberated.

Entropy Change ($\Delta S$)

The measure of the change in the degree of disorderliness or randomness of a reaction.

Entropy Jump

A phenomenon where a physical phase transition is directly bypassed, such as in sublimation where a solid transitions straight into a gas.

Faraday's Constant ($F$)

The physical constant representing the charge per mole of electrons, equal to $96485\,C\,mol^{-1}$.

Bond Energy

The average energy needed to break $1\,mole$ of a chemical bond in its gaseous state.

Glass Calorimeter

A simple and inexpensive instrument commonly used to measure the heat of chemical reactions.

Bomb Calorimeter

A highly sensitive reaction vessel mainly used to measure the heat of combustion and analyze the energy content of food.

Standard Enthalpy of Formation ($\Delta H^\circ_f$)

The heat change when $1\,mole$ of a substance is formed from its constituent elements under standard conditions ($298\,K$ and $1\,atm$).

Standard Enthalpy of Combustion ($\Delta H^\circ_c$)

The heat liberated when $1\,mole$ of a substance is completely burned in oxygen under standard conditions, which is always exothermic ($\Delta H^\circ_c < 0$).

Standard Enthalpy of Solution ($\Delta H^\circ_{sol}$)

The heat absorbed or evolved when $1\,mole$ of a substance is completely dissolved in water.

Lattice Energy

The endothermic process energy required to break down a solid solute into its individual ions during dissolution.

Hydration Energy

The exothermic process energy liberated when separated solute ions become surrounded by water molecules during dissolution.

Standard Enthalpy of Neutralization ($\Delta H^\circ_{neut}$)

The heat released when $1\,mole$ of $H^+$ reacts with $1\,mole$ of $OH^-$ to produce $1\,mole$ of $H_2O$, which equals $-57.1\,kJ\,mol^{-1}$ for strong acid-strong base reactions.

Hess's Law

Also known as the law of constant heat summation, it states that the overall enthalpy change of a reaction is constant regardless of the route or number of steps taken.