Disappearance rate ($v_{\mathrm{A}}=-d[\mathrm{A}]/dt$)

The disappearance rate of a reactant A is its positive net loss of concentration per unit time, $v_{\mathrm{A}}=-d[\mathrm{A}]/dt$. For the fixed-volume, single-chemical reaction setting of reaction rate, consuming $a$ units of A per conversion gives $v_{\mathrm{A}}=av$. The factor belongs to the stoichiometry; stating it is essential when quoting a rate constant. A negative net disappearance rate means that A is accumulating.