Equations

ΔU

Change in internal energy, equal to the heat added to the system plus the work done on the system.

q

Heat exchange, often represented in thermodynamics.

w

Work done on or by the system, can be calculated as work equals negative pressure times change in volume (w = -PΔV).

H

Enthalpy, defined as the total heat content of a system (H = U + PV).

ΔH

Change in enthalpy, equivalent to the heat exchanged at constant pressure (ΔH = q at constant pressure).

msΔT

Formula for calculating heat absorbed or released, where m is mass, s is specific heat capacity, and ΔT is the change in temperature.

ΔH°rxn

Standard enthalpy change of the reaction, calculated by subtracting the sum of standard enthalpies of formation of reactants from that of products.

ΔHf°

Standard enthalpy of formation, the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

Constant Pressure

A condition under which ΔH is equal to the heat exchanged in a process.

PΔV

The work done on or by a system when it expands or contracts at constant pressure.