Chem- Thermochemistry Chapter 10

Internal energy (E)

The sum of all kinetic and potential energy of an object.

Thermochemistry

The study of the energy changes that accompany chemical reactions.

First law of thermodynamics

Energy cannot be created or destroyed; it can only change form. The total energy of the universe is constant.

System

The part of the universe that is the focus of a thermochemical study.

Surroundings

Everything that is not part of the system.

State function

A property that depends only on the current state of a system, not on the path taken to reach it.

Heat (q)

Energy in the process of being transferred from a higher-temperature object to a lower-temperature object.

Work (w)

A force exerted through a distance.

Thermal energy

The portion of internal energy proportional to absolute temperature; the sum of the kinetic energies of the particles.

Isolated system

A system where neither matter nor energy can be exchanged with the surroundings (e.g., thermos of soup).

Closed system

A system where energy can flow but matter cannot (e.g., cup of soup with a lid).

Open system

A system where both energy and matter can flow freely (e.g., open cup of soup).

Exothermic process

A process in which heat flows from the system into the surroundings (delta H < 0).

Endothermic process

A process in which heat flows from the surroundings into the system (delta H > 0).

Enthalpy (H)

The sum of a system's internal energy and its pressure-volume product; H = E + PV.

Enthalpy change (delta H)

The heat transferred into or out of a system at constant pressure.

Enthalpy of fusion (delta H fus)

The energy required to convert one mole of solid to liquid at the melting point.

Enthalpy of vaporization (delta H vap)

The energy required to convert one mole of liquid to vapor at the boiling point.

Heating curve

A plot of temperature versus heat added; flat segments are phase changes, sloped segments are temperature changes.

Heat capacity

The quantity of heat needed to raise an object's temperature by 1 degree C.

Specific heat (c_s)

The heat needed to raise the temperature of 1 gram of a substance by 1 degree C.

Molar heat capacity (c_P)

The heat needed to raise the temperature of 1 mole of a substance by 1 degree C.

Heat sink

Matter that can absorb energy without changing phase or significantly changing temperature (e.g., water).

Calorimetry

The experimental determination of the energy transferred during a phase change or chemical process.

Calorimeter

A device used to measure the absorption or release of energy by a phase change or chemical process.

Enthalpy of reaction (delta H rxn)

The enthalpy change that accompanies a chemical reaction; also called the heat of reaction.

Bomb calorimeter

A sealed, constant-volume steel vessel used to measure the energy released during a combustion reaction.

Calorimeter constant (C_calorimeter)

The heat capacity of the bomb calorimeter and all its components; the energy needed to raise its temperature by 1 degree C.

Hess's law

The enthalpy change of a multistep process equals the sum of the enthalpy changes of the individual steps.

Standard conditions

Gases at 1 bar and solutions at 1 M (data tables often use 25 degrees C).

Standard state

The most stable physical form of a substance under standard conditions (e.g., O2 gas, H2O liquid, C as graphite).

Standard enthalpy of formation (delta H f)

The enthalpy change when one mole of a substance is formed from its constituent elements in their standard states.

Formation reaction

The reaction that forms one mole of a compound from its elements in their standard states.

delta H f of an element in its standard state

Equals zero; it is the reference (zero point) for enthalpy.

Bond energy

The energy required to break one mole of a particular bond in the gas phase.

Breaking bonds

An endothermic process (requires energy, positive delta H).

Forming bonds

An exothermic process (releases energy, negative delta H).

Enthalpy of solution (delta H solution)

The overall enthalpy change when a solute dissolves in a solvent; can be endothermic or exothermic.

Born-Haber cycle

A series of steps with enthalpy changes describing the formation of an ionic solid from its constituent elements.

Lattice energy

The energy associated with forming one mole of an ionic solid from its gaseous ions.

Fuel value

The energy released per gram of a substance.

Fuel density

The quantity of energy released per unit volume of a liquid fuel.

Calorie (Cal)

A food energy unit; 1 Cal = 1000 cal = 1 kcal = 4.184 kJ.