Chemical kinetics is a branch of physical chemistry that constitutes an essential part of undergraduate education. In general, a complex and expensive experimental apparatus is indispensable for observing the kinetics of a chemical process owing to the continuity of chemical reactions. Thus, intuitive visualization of the chemical kinetics using a simple experimental apparatus is challenging. Herein, a portable flow reactor was designed and used to observe the chemical kinetics of a first-order process. Continuous chemical reactions were visualized via the flow reactor as static patterns with color gradients. The thermochromism of the rhodamine B salicylaldehyde hydrazone zinc(II) complex was visualized via the flow reactor and found to follow first-order kinetics. The color gradients of static reaction patterns were analyzed by comparing them with standard color cards, and the kinetic parameters, such as the reaction rate constants at different temperatures and the activation energy, were determined. By performing this experiment, students can learn about flow chemistry, photochromism, and thermochromism. The interesting experimental process and distinct color changes can hold the students' attention. The two calculation methods can help the students better understand the rate equation of a first-order reaction. The experimental apparatus is low cost and commercially available, which is beneficial for the widespread use of this experiment.