heat capacity

Meaning: Heat capacity measures how much heat an object or sample takes in per degree of temperature rise. A large value means the sample absorbs a lot of heat for a small temperature change. It scales with the amount of material, so it is extensive. Dividing by mass gives specific heat (c); dividing by moles gives molar heat capacity. Water has a high specific heat, about 4.18 J/(g·K), largely because of hydrogen bonding, so it resists temperature change. For gases, the value depends on conditions: Cp (constant pressure) is larger than Cv (constant volume).

Equation: q = CΔT = mcΔT, where q is heat absorbed (J), C is heat capacity (J/K), m is mass (kg, or g if c uses grams), c is specific heat (J/(kg·K) or J/(g·K)), and ΔT is the temperature change (K; a change of 1 K equals a change of 1 °C).

On the MCAT: Calorimetry passages drop a hot metal into water; set heat lost equal to heat gained and solve for the final temperature or for c. Heating curves use q = mcΔT on the sloped segments and q = mL on the flat phase-change segments. Comparison questions ask which substance warms more for the same heat: the one with the smaller c.

Common confusion: Students mix up heat capacity (J/K, depends on sample size) with specific heat (per unit mass, a property of the substance). Also, on a flat segment of a heating curve heat is still being added, but ΔT = 0, so mcΔT does not apply; use mL.