Chapter 7: Thermochemistry

thermochemistry

The study of the relationship between chemistry and energy.

energy

The capacity to do work.

work

(w) The action of a force through a distance.

heat

(q) The flow of energy caused by a temperature difference.

kinetic energy

The energy associated with motion of an object.

thermal energy

A type of kinetic energy associated with the temperature of an object, arising from the motion of individual atoms or molecules in the object; see also heat.

potential energy

The energy associated with the position or composition of an object.

chemical energy

The energy associated with the relative positions of electrons and nuclei in atoms and molecules.

law of conservation of energy

A law stating that energy can neither be created nor destroyed, only converted from one form to another.

system

In thermodynamics, the portion of the universe that is singled out for investigation.

surroundings

In thermodynamics, everything in the universe that exists outside the system under investigation.

joule (J)

(J) The SI unit for energy.

calorie (cal)

(cal) A unit of energy defined as the amount of energy required to raise 1 g of water 1 °C; equal to 4.184 J.

kilowatt-hour (kWh)

(kWh) An energy unit used primarily to express large amounts of energy produced by the flow of electricity; equal to 3.60 X 10⁶ J.

thermodynamics

The general study of energy and its interconversions.

first law of thermodynamics

The law stating that the total energy of the universe is constant.

internal energy (E)

(E) The sum of the kinetic and potential energies of all the particles that compose a system.

state function

A function whose value depends only on the state of the system, not on how the system got to that state.

thermal equilibrium

The point at which there is no additional net transfer of heat between a system and its surroundings.

heat capacity (C)

(C) The quantity of heat required to change a system’s temperature by 1 °C.

specific heat capacity(C_s)

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

molar heat capacity

The amount of heat required to raise the temperature of 1 mol of a substance by 1 °C

pressure-volume work

The work that occurs when a volume change takes place against an external pressure.

calorimetry

The experimental procedure used to measure the heat that evolves in a chemical reaction.

bomb calorimeter

A piece of equipment designed to measure ΔE_rxn for combustion reactions at constant volume.

enthalpy (H)

(H ) The sum of the internal energy of a system and the product of its pressure and volume.

endothermic reaction

chemical or physical process that absorbs heat from its surroundings.

exothermic reaction

chemical or physical process that releases heat into surroundings

enthalpy (heat) of reaction (A H_rxn)

chemical or physical process that absorbs heat from its surroundings.

coffee-cup calorimeter

chemical or physical process that absorbs heat from its surroundings.

Hess's law

chemical or physical process that absorbs heat from its surroundings.

standard state

For a gas, the standard state is the pure gas at a pressure of exactly 1atm; for a liquid or solid, the standard state is the pure substance in its most stable form at a pressure of 1 atm and thetemperature of interest (often taken to be 25 °C); for a substance in solution, the standard state is a concentration of exactly 1 M.

standard enthalpy change (AH°)

(∆H°) The change in enthalpy for a process when all reactants and products are in their standard states.

standard enthalpy of formation (AH^o_f)

𝐻(ΔHf∘) The change in enthalpy when 1 mol of a compound forms from its constituent elements in their standard states.

standard heat of formation

The change in enthalpy when 1 mol of a compound forms from its constituent elements in their standard states.