Abstract While teaching the physical chemistry for the first and second year undergraduate students, the understanding of different time scales is important in the study of the molecular reaction dynamics. Here, the expression of rate constant derived from the transition state theory was utilized to estimate the time scales of different dynamic processes, where the rotation of carbon/carbon single bond in ethane and the hydrogen bonding exchanging in water molecules were employed as the examples. The estimation of these time scales is critical for the students to gain a clear physical picture of different dynamic processes. And it also helps to strengthen their understanding of the important formulas and the applications of transition state theory in the chemical systems.