Chapter 6- Thermochemistry: Energy Flow and Chemical Change

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=qP.

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

heat (q) (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 1K

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 energy (first law of thermodynamics)

A basic observation that the total energy of the universe is constant; thus, ΔEuniverse = ΔEsystem + ΔEsurroundings = 0.

molar heat capacity (Cm)

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

pressure-volume 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 1K

standard enthalpy of formation (ΔH°f)

also called the heat of formation; the enthalpy change occurring when 1mol of a compound forms from its elements with all components in their standard states

standard enthalpy of reaction (ΔH°rxn)

also called the 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, 1M for dissolved species, or the pure substances 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 the 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