The problem of the temperature field in the round cross section of the catalyst space in conducting heterogeneous chemical reactions with an important heat effect is examined. A conclusion is drawn concerning the approximateness of its solution based on postulating constant heat release (heat absorption) over the section of the bed during the chemical reaction. It is also shown that the solution based on linearization of the exponent in the Arrhenius equation leads to unacceptably large errors. An approximate analysis of the process is performed with consideration of the dependence of the heat effect on the temperature: the analytical correlation of the temperature and coordinates in the cross section of the catalyst zone was found. The temperature curves are plotted for constant and variable (over the section of the catalyst bed) heat effects: their significant variance is demonstrated. It is shown that the solution based on a constant heat effect gives an understated result.