Final answer:
At constant pressure with increased temperature, volumetric flowrate at the reactor exit is greater due to thermal expansion of gases. At constant temperature with decreased pressure, volumetric flowrate at the exit can be lesser if the reaction results in fewer product moles than reactant moles, as there's less substance to flow, despite the gas expansion.
Step-by-step explanation:
For a gas-phase chemical reaction A ⟶ B happening in a chemical reactor at constant pressure with a temperature increase, the volumetric flowrate at the exit would be greater than at the entrance. This is because, according to Gay-Lussac's Law, at constant pressure, the volume of a gas is directly proportional to its temperature. So if the temperature increases and pressure remains constant, the volume (and therefore volumetric flowrate) will increase.
Conversely, for a reaction at constant temperature with a decrease in pressure from entrance to exit, the volumetric flowrate would be less at the exit. Avogadro's Law tells us that the volume of a gas is directly proportional to the number of moles of the gas at constant temperature and pressure. With a pressure decrease and constant temperature, the gas would expand, but since the reactor is open and the gas is flowing, the available volume is essentially unlimited; thus, the volumetric flowrate is more influenced by the number of moles, and if the chemical reaction reduces the number of moles (such as when a reaction has fewer product moles than reactant moles), then the flowrate decreases.