Medical College Admission Test (MCAT) General Chemistry Practice Exam 2025 - Free MCAT Chemistry Practice Questions and Study Guide

Temperature, in a molecular context, is defined as a measurement of the average kinetic energy of the molecules in a substance. This means that temperature reflects how fast the molecules are moving—higher temperatures indicate faster molecular motion, while lower temperatures indicate slower movement.

When the thermal energy of a substance increases, the average speed of its molecules increases as well, resulting in a higher temperature reading. Conversely, if the thermal energy decreases, the average kinetic energy also decreases, leading to a lower temperature. This relationship is fundamental to understanding heat transfer and the behavior of gases, liquids, and solids at various temperatures.

The other options do not accurately capture the definition of temperature in a molecular context. For instance, stating temperature as the total energy of molecules conflates kinetic energy with potential energy and does not specify the average kinetic energy component relevant to temperature. Similarly, defining temperature by the volume occupied by molecules overlooks the motion aspect and does not include any information about energy, and referring to the weight of molecules does not relate to temperature at all.