# Errata: Extra term \xi f in derivation of reaction rate equations in Section 2.1

Location: page 35, line 16, -11

The term $\xi_f$ in the displayed equations for $n_\text{AB}(t + dt)$ and $[\text{AB} ](t+dt) - [ \text{AB} ](t)$ should be removed. In the derivation of the reaction rate equations, the propensity functions are evaluated at the current state.

The corrected equations are

$n_\text{AB}(t + dt) = n_\text{AB}(t) + a_f({\color{blue} q}) dt - a_r(q) dt,$

and

\begin{align} [\text{AB}](t + dt) - [\text{AB}](t) &= \Bigl( a_f({\color{blue} q}, t) - a_r(q) \Bigr) / \Omega \cdot dt \\ &= \Bigl( k_f n_\text{A} n_\text{B} / \Omega^2 - k_r n_\text{AB} / \Omega \Bigr)\, dt \\ &= \Bigl( k_f [\text{A}] [\text{B}] - k_r [\text{AB}] \Bigr)\, dt. \end{align}

(Contributed by D. Del Vecchio, 10 Sep 2014)

This error appears in version 1.1a and earlier versions of the text.