Preferred Label : rate of reaction;
Detailed label : rate of reaction, v;
IUPAC definition : For the general chemical reaction: \[a\,{A} b\,{B}\rightarrow p\,{P} q\,{Q} ...\]
occurring under constant-volume conditions, without an appreciable build-up of reaction
intermediates, the rate of reaction v is defined as: \[\nu -\frac{1}{a} \frac{\mathrm{d}{[A]}}{\mathrm{d}t}
- \frac{1}{b} \frac{\mathrm{d}{[B]}}{\mathrm{d}t} \frac{1}{p} \frac{\mathrm{d}{[P]}}{\mathrm{d}t}
\frac{1}{q} \frac{\mathrm{d}{[Q]}}{\mathrm{d}t}\] where symbols placed inside square
brackets denote amount (or amount of substance) concentrations (conventionally expressed
in units of mol dm-3). The symbols R and r are also commonly used in place of v. It
is recommended that the unit of time should always be the second. In such a case the
rate of reaction differs from the rate of increase of concentration of a product P
by a constant factor (the reciprocal of its coefficient in the stoichiometric equation,
p) and from the rate of decrease of concentration of the reactant A by α-1. The quantity:
\[\overset{{.}}{\xi } \frac{\mathrm{d}\xi }{\mathrm{d}t}\] defined by the equation:
\[\overset{{.}}{\xi } -\frac{1}{a} \frac{\mathrm{d}n_{{A}}}{\mathrm{d}t} - \frac{1}{b}
\frac{\mathrm{d}n_{{B}}}{\mathrm{d}t} \frac{1}{p} \frac{\mathrm{d}n_{{P}}}{\mathrm{d}t}
\frac{1}{q} \frac{\mathrm{d}n_{{Q}}}{\mathrm{d}t}\] (where n A designates the amount
of substance A, conventionally expressed in units of mole) may be called the 'rate
of conversion' and is appropriate when the use of concentrations is inconvenient,
e.g. under conditions of varying volume. In a system of constant volume, the rate
of reaction is equal to the rate of conversion per unit volume throughout the reaction.
For a stepwise reaction this definition of 'rate of reaction' (and 'extent of reaction',
ξ) will apply only if there is no accumulation of intermediate or formation of side
products. It is therefore recommended that the term 'rate of reaction' be used only
in cases where it is experimentally established that these conditions apply. More
generally, it is recommended that, instead, the terms 'rate of disappearance' or 'rate
of consumption' of A (i.e. -d[A]/dt, the rate of decrease of concentration of A) or
'rate of appearance' of P (i.e. d[P]/dt, the rate of increase of concentration of
product P) be used, depending on the concentration change of the particular chemical
species that is actually observed. In some cases reference to the chemical flux observed
may be more appropriate. The symbol v (without lettered subscript) should be used
only for rate of reaction; v with a lettered subscript (e.g. v A) refers to a rate
of appearance or rate of disappearance (e.g. of the chemical species A).;
Origin ID : R05156;
See also
For the general chemical reaction: \[a\,{A} b\,{B}\rightarrow p\,{P} q\,{Q} ...\]
occurring under constant-volume conditions, without an appreciable build-up of reaction
intermediates, the rate of reaction v is defined as: \[\nu -\frac{1}{a} \frac{\mathrm{d}{[A]}}{\mathrm{d}t}
- \frac{1}{b} \frac{\mathrm{d}{[B]}}{\mathrm{d}t} \frac{1}{p} \frac{\mathrm{d}{[P]}}{\mathrm{d}t}
\frac{1}{q} \frac{\mathrm{d}{[Q]}}{\mathrm{d}t}\] where symbols placed inside square
brackets denote amount (or amount of substance) concentrations (conventionally expressed
in units of mol dm-3). The symbols R and r are also commonly used in place of v. It
is recommended that the unit of time should always be the second. In such a case the
rate of reaction differs from the rate of increase of concentration of a product P
by a constant factor (the reciprocal of its coefficient in the stoichiometric equation,
p) and from the rate of decrease of concentration of the reactant A by α-1. The quantity:
\[\overset{{.}}{\xi } \frac{\mathrm{d}\xi }{\mathrm{d}t}\] defined by the equation:
\[\overset{{.}}{\xi } -\frac{1}{a} \frac{\mathrm{d}n_{{A}}}{\mathrm{d}t} - \frac{1}{b}
\frac{\mathrm{d}n_{{B}}}{\mathrm{d}t} \frac{1}{p} \frac{\mathrm{d}n_{{P}}}{\mathrm{d}t}
\frac{1}{q} \frac{\mathrm{d}n_{{Q}}}{\mathrm{d}t}\] (where n A designates the amount
of substance A, conventionally expressed in units of mole) may be called the 'rate
of conversion' and is appropriate when the use of concentrations is inconvenient,
e.g. under conditions of varying volume. In a system of constant volume, the rate
of reaction is equal to the rate of conversion per unit volume throughout the reaction.
For a stepwise reaction this definition of 'rate of reaction' (and 'extent of reaction',
ξ) will apply only if there is no accumulation of intermediate or formation of side
products. It is therefore recommended that the term 'rate of reaction' be used only
in cases where it is experimentally established that these conditions apply. More
generally, it is recommended that, instead, the terms 'rate of disappearance' or 'rate
of consumption' of A (i.e. -d[A]/dt, the rate of decrease of concentration of A) or
'rate of appearance' of P (i.e. d[P]/dt, the rate of increase of concentration of
product P) be used, depending on the concentration change of the particular chemical
species that is actually observed. In some cases reference to the chemical flux observed
may be more appropriate. The symbol v (without lettered subscript) should be used
only for rate of reaction; v with a lettered subscript (e.g. v A) refers to a rate
of appearance or rate of disappearance (e.g. of the chemical species A).
