The
standard enthalpy change of reaction (denoted Δ
rH⦵) is the
enthalpyIn thermodynamics and molecular chemistry, the enthalpy is a thermodynamic property of a thermodynamic system. It can be used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure...
change that occurs in a system when one mole of matter is transformed by a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
under standard conditions.
For a generic chemical reaction
- −vA A + −vB B + ... → vP P + vQ Q ...
the standard enthalpy change of reaction Δ
rH⦵ is related to the
standard enthalpy change of formationThe standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states...
Δ
fH⦵ of the reactants and products by the following equation:
In this equation,
vB is the stoichiometric coefficient of entity B.
A common
standard enthalpy change is the
standard enthalpy change of formationThe standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states...
, which has been determined for a vast number of substances.
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The
standard enthalpy change of reaction (denoted Δ
rH⦵) is the
enthalpyIn thermodynamics and molecular chemistry, the enthalpy is a thermodynamic property of a thermodynamic system. It can be used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure...
change that occurs in a system when one mole of matter is transformed by a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
under standard conditions.
For a generic chemical reaction
- −vA A + −vB B + ... → vP P + vQ Q ...
the standard enthalpy change of reaction Δ
rH⦵ is related to the
standard enthalpy change of formationThe standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states...
Δ
fH⦵ of the reactants and products by the following equation:
In this equation,
vB is the stoichiometric coefficient of entity B.
Reactions with standard values
A common
standard enthalpy change is the
standard enthalpy change of formationThe standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states...
, which has been determined for a vast number of substances. The enthalpy change of any reaction under any conditions can be computed, given the
standard enthalpy change of formationThe standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states...
of all of the reactants and
productA product is a substance that forms as a result of a biological- or chemical reaction. While the end product of some chemical reactions may be the result of a relatively rapid reaction, nanoseconds to seconds, chemical equilibria in complex systems may require years or even centuries to be...
s. Other reactions with standard enthalpy change values include combustion (
standard enthalpy change of combustionThe standard enthalpy of combustion is the enthalpy change when one mole of a substance completely reacts under standard thermodynamic conditions...
), neutralisation (
standard enthalpy change of neutralisationThe standard enthalpy change of neutralisation is the change in enthalpy that occurs when an acid and base undergo a neutralisation reaction to form one mole of water under standard conditions , i.e. react to produce water and a salt...
), and solution (standard enthalpy change of solution).
ds
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