Thermodynamic Concepts and Energy Transfer

bomb calorimeter

Instrument used to measure the heat of combustion of a reaction.

bond energy, BE

The energy needed to break a mole of a specific type of bond; also called bond enthalpy.

bond enthalpy

The enthalpy change, ∆H, associated with breaking a specific bond in 1 mol of gaseous molecules.

Born-Haber cycle

A thermodynamic cycle that uses Hess's law, ionization energy, electron affinity, and the energies of other processes to calculate the lattice energy of an ionic compound.

calorie, cal

A unit of energy that is equal to 4.184 J; the amount of energy required to raise the temperature of 1 g of water 1°C.

Calorie, Cal

A unit of energy used in the field of nutrition that is equal to exactly 1000 cal, 1 kcal, 4184 J, or 4.184 kJ.

calorimetry

A laboratory technique for quantifying heat transfer between substances by measuring the temperature changes of the substances involved.

constant-volume calorimetry

A laboratory technique for measuring changes in heat transfer between substances by measuring the temperature changes of the substances involved.

endothermic process

A process in which heat is absorbed from outside the system and ΔH is positive.

energy

The capacity to do work or transfer heat.

enthalpy, H

The sum of internal energy of a system and the product of its pressure and volume change.

exothermic process

A process in which heat is transferred from the system to the surroundings and the change in enthalpy is negative.

first law of thermodynamics

The energy of the universe is constant.

heat, q

The flow of energy that causes a temperature change in an object or its surroundings.

Hess's law

When two or more processes combine to give a resulting process, their enthalpy changes add to give the enthalpy change for the resulting process.

internal energy, U

The sum of all kinetic and potential energies of a system.

joule, J

The SI unit of energy; it takes 4.184 J to raise the temperature of 1 g of water 1°C.

kinetic energy, KE

The energy of motion.

lattice energy, ΔH°L

The energy released when gas-phase ions combine to form a solid ionic compound.

law of conservation of energy

Energy cannot be created or destroyed.

mechanical energy

Energy in an object that is attributable to its motion, position, or both.

path function

A function that is dependent on the sequence of steps that move the system from its initial state to its final state.

potential energy

The energy of an object that is related to its position.

pressure-volume work

The work done on or by a system when there is a volume change against an external pressure.

specific heat, c

The quantity of heat required to raise the temperature of 1 g of a substance by 1°C.

standard enthalpy of formation, ΔH°f

The enthalpy change in the formation of 1 mol of a compound from its elements in their standard states.

standard state

The state in which the substance is most stable at 25°C (298 K) and 1 atm pressure.

state function

A function that is independent of the path taken to achieve its value.

sublimation

The phase change from solid to gas.

surroundings

The part of the universe that is separate from a system of study.

system

A specified portion of the universe that is studied.

work, w

The energy resulting from a force acting on an object over a distance.