Heat capacity

Definition and units

Heat capacity (C) is defined as the ratio of the heat added Q to the resulting temperature change ΔT: C = Q / ΔT. It is an extensive quantity: larger objects generally have larger heat capacities. The SI unit is joules per kelvin (J·K−1). When referred to mass, the intensive form is specific heat capacity c = C / m, often expressed in J·kg−1·K−1. When normalized by amount of substance it is called molar heat capacity (J·mol−1·K−1). Common mass units include the gram or kilogram and the related idea of mass factors into conversion between C and c.

Characteristics and examples

Heat capacity depends on material, temperature and phase. Solids, liquids and gases show different behavior and heat capacities of most substances vary with temperature. Near phase changes, latent heat dominates and the simple C = Q/ΔT description must be augmented to account for energy absorbed without temperature change.

• Water has a relatively high specific heat and therefore moderates temperature changes in nature and technology.
• Metals typically have lower specific heats and heat up or cool down more quickly for the same energy input.
• Two common laboratory distinctions are C_p (constant pressure) and C_v (constant volume), important in gases and thermodynamic calculations.

History and measurement

Early quantitative study of heat capacities grew from 18th–19th century calorimetry. Scientists established that different substances require different amounts of heat per degree. Practical measurement uses calorimeters and techniques such as differential scanning calorimetry; for gases, measurements at fixed pressure or volume yield C_p and C_v respectively. Empirical rules like the Dulong–Petit law approximate molar heat capacities of many solids at high temperature.

Uses and significance

Heat capacity appears across many fields. In climate science, the large heat capacity of oceans slows temperature changes. In engineering and electronics, materials are chosen to store or dissipate heat effectively. Thermal energy storage systems exploit materials with high specific heat for buffering, while cookware, building materials and thermal insulation are selected based on their heat capacity properties.

Distinctions and notable facts

Important distinctions: heat capacity (extensive) vs specific or molar heat capacity (intensive); constant-pressure vs constant-volume values; and heat capacity versus latent heat associated with phase changes. Accurate use requires attention to units and to temperature dependence in precise calculations.

For broader background and data tables on specific substances, consult reference collections and standard thermophysical property sources: materials databases, general references on heat and temperature, or technical tables listing values per gram or per mass.