The standard enthalpy of combustion is the enthalpy change when one mole of a reactant completely burns in oxygen under standard thermodynamic conditions (although experimental values are usually obtained under different conditions and subsequently adjusted). By definition, the combustion reactions are always particularly exothermic and so enthalpies of combustion are always negative, although the values for individual combustions may vary.
The most common way of calculating the enthalpy change of combustion (or formation) is by using a Hess cycle or by using numerical based bond enthalpies. It is commonly denoted as or . When the enthalpy required is not a combustion, it can be denoted as . Enthalpies of combustion are typically measured using bomb calorimetry, and have units of energy (typically kJ); strictly speaking, the enthalpy change per mole of substance combusted is the standard molar enthalpy of combustion (which typically would have units of kJ mol−1).
Famous quotes containing the words standard, change and/or combustion:
“I find it interesting that the meanest life, the poorest existence, is attributed to God’s will, but as human beings become more affluent, as their living standard and style begin to ascend the material scale, God descends the scale of responsibility at a commensurate speed.”
—Maya Angelou (b. 1928)
“Suddenly I’m dogmatic. Why does my status change every time you get a new woman, Jack?”
—Warren Beatty (b. 1937)
“The night has been unruly. Where we lay,
Our chimneys were blown down, and, as they say,
Lamentings heard i’ th’ air, strange screams of death,
And prophesying with accents terrible
Of dire combustion and confused events,
New-hatched to the woeful time.”
—William Shakespeare (1564–1616)