For an exothermic chemical reaction taking place in an open beaker at constant atmospheric pressure,

Question

For an exothermic chemical reaction taking place in an open beaker at constant atmospheric pressure, which of the following sets of thermodynamic parameters is unconditionally true?

Professor PC Thomas Classes · Answer

(c) : An open beaker implies the reaction is occurring at constant pressure. For a constant pressure process, the heat exchanged ($q_p$) is exactly equal to the enthalpy change ($\Delta_r H$). Because the reaction is exothermic, it releases heat to the surroundings. Therefore, both $q_p$ and $\Delta_r H$ must be strictly negative (less than zero).