A first-order heterogeneous reaction \( A \rightarrow B \) is conducted using a porous spherical catalyst under isothermal conditions, where intraphase diffusion governs the reaction rate. At a bulk A concentration of 0.3 mol L\(^{-1}\), the observed reaction rate in a 3 mm diameter catalyst particle is 0.2 mol s\(^{-1}\) L\(^{-1}\) catalyst volume. At a bulk A concentration of 0.1 mol L\(^{-1}\), the observed reaction rate in a 6 mm diameter catalyst particle, in mol s\(^{-1}\) L\(^{-1}\) catalyst volume, is: