CHEM-UA 125 Chapter 6 Vocabulary

biomass fuel

A fuel composed of biological materials such as plant and animal matter.

calorie (cal)

A unit of energy defined as exactly 4.184 joules; originally defined as the heat needed to raise the temperature of 1 g of water 1°C (from 14.5°C to 15.5°C).

calorimeter

A device used to measure the heat released or absorbed by a physical or chemical process taking place within it.

change in enthalpy (ΔH)

The change in the system’s internal energy plus the product of the constant pressure and the change in volume: ΔH = ΔE + PΔV; alternatively, the heat lost or gained at constant pressure: ΔH = q_P.

endothermic process

A process that occurs with an absorption of heat from the surroundings and therefore an increase in the enthalpy of the system (ΔH > 0).

enthalpy (H)

A thermodynamic quantity that is equal to the system’s internal energy plus the product of the pressure and volume.

enthalpy diagram

A graphic depiction of the enthalpy change of a system.

exothermic process

A process that occurs with a release of heat to the surroundings and therefore a decrease in the enthalpy of the system (ΔH < 0).

formation equation

An equation in which 1 mole of a compound forms from its elements.

fossil fuel

Any fuel, including coal, petroleum, and natural gas, derived from the products of the decay of dead organisms.

heat (q)

(also thermal energy) The energy transferred between objects because of a difference in their temperatures only.

heat capacity (C)

The quantity of heat required to change the temperature of an object by 1 K.

Hess’s law

A law stating that the enthalpy change of an overall process is the sum of the enthalpy changes of the individual steps.

internal energy (E)

The sum of the kinetic and potential energies of all the particles in a system.

joule (J)

The SI unit of energy; 1 J = 1 kg · m²/s².

law of conservation of energy

(also first law of thermodynamics) A basic observation that the total energy of the universe is constant; thus, ΔE_universe = ΔE_system + ΔE_surroundings = 0.

molar heat capacity (Cm)

The quantity of heat required to change the temperature of 1 mol of a substance by 1 K.

photovoltaic cell

A device capable of converting light directly into electricity.

pressure-volume work

(also PV work) A type of mechanical work done when a volume change occurs against an external pressure.

specific heat capacity (c)

The quantity of heat required to change the temperature of 1 gram of a substance or material by 1 K.

standard enthalpy of formation ΔH°f

(also standard heat of formation) The enthalpy change occurring when 1 mol of a compound forms from its elements with all components in their standard states.

standard enthalpy of reaction ΔH°rxn

(also standard heat of reaction) The enthalpy change that occurs during a reaction when all components are in their standard states.

standard state

A set of specific conditions used to compare thermodynamic data: 1 atm for gases behaving ideally, 1 M for dissolved species, or the pure substance for liquids and solids.

state function

A property of a system determined only by the system’s current state, regardless of how it arrived at that state.

surroundings

All parts of the universe other than the system being considered.

system

The defined part of the universe under study.

thermochemical equation

A balanced chemical equation that includes the enthalpy change for the reaction

thermochemistry

The branch of thermodynamics that focuses on the heat involved in chemical and physical change.

thermodynamics

The study of energy and its transformations.

work (w)

The energy transferred when an object is moved by a force.