In a first-order reaction, the instantaneous rate of reaction is given by the equation: \[ \text{Rate} = k [A] \] The slope of the graph at point C represents the rate constant \( k \), and thus, the instantaneous rate is directly related to the slope. The slope \( m \) of the graph represents the rate.
Consider a reaction $ A + R \rightarrow Product $. The rate of this reaction is measured to be $ k[A][R] $. At the start of the reaction, the concentration of $ R $, $[R]_0$, is 10-times the concentration of $ A $, $[A]_0$. The reaction can be considered to be a pseudo first order reaction with assumption that $ k[R] = k' $ is constant. Due to this assumption, the relative error (in %) in the rate when this reaction is 40% complete, is ____. [$k$ and $k'$ represent corresponding rate constants]