temperature

Meaning: Temperature reflects the average kinetic energy of the particles in a sample. A higher temperature means the particles move faster on average. It is intensive, so it does not depend on how much substance is present. Heat flows spontaneously from the higher-temperature object to the lower-temperature one until thermal equilibrium is reached. During a phase change, added heat goes into potential energy (overcoming intermolecular attractions), so temperature stays constant.

Equation: KEavg = (3/2)kBT, where KEavg is the average translational kinetic energy per ideal gas molecule (J), kB is the Boltzmann constant (1.38 × 10⁻²³ J/K), and T is absolute temperature (K).

On the MCAT: Gas law questions require kelvins, where K = °C + 273. Doubling the kelvin temperature doubles average kinetic energy, and the root-mean-square speed rises by a factor of √2. Maxwell-Boltzmann graphs shift right and flatten as temperature rises. Heating curves show flat segments at melting and boiling. Rate constants usually increase with temperature, and Le Châtelier reasoning predicts how K shifts.

Common confusion: Temperature is not heat. Heat is energy transferred because of a temperature difference, while temperature is a property of the sample. Going from 20 °C to 40 °C does not double the kinetic energy; only the kelvin value (293 K to 313 K) matters. At the same temperature, different gases share the same average kinetic energy, but lighter molecules move faster.