Specific heat capacity (Symbol: H)) is the measure of the heat energy required to raise the temperature of a specific quantity of a substance (thus, the name “specific” heat) by specific amount, usually one kelvin. A kelvin is a unit increment of thermodynamic temperature and is precisely equal to an increment of one degree Celsius. The specified quantity of matter can be in terms of either mass or moles (which is a certain number of atoms or molecules).

The typical units for measuring specific heat capacity are either the joule per gram per kelvin (J g^–1 K^–1) or joule per mole per kelvin (J mol^–1 K^–1). The various SI prefixes can create variations of these units (such as kJ kg^–1 K^–1 and kJ mol^–1 K^–1).  Other units of measure are often employed in the measure of specific heat capacity. These include calories and BTUs for energy, pounds mass for quantity, and degree Fahrenheit (°F) for the increment of temperature.

There are two distinctly different experimental conditions under which specific heat capacity is measured. The specific heat of substances are typically measured under constant pressure (Symbol: C_pH). However, gases and liquids are typically also measured at constant volume (Symbol: C_vH).  Especially for gases, C_vH produces values that are quite different from C_pH. The specific heat capacities of substances comprised of molecules (distinct from the monatomic gases) are not fixed constants and vary somewhat depending on temperature.  Accordingly, the starting temperature at which the measurement is made is usually also specified. Thus, examples of common ways to cite the specific heat of a substance are as follows:

Water (liquid): C_pH = 4.1855 J g^–1 K^–1 (15 °C), and…
Water (liquid): C_pH = 75.327 J mol^–1 K^–1 (25 °C)

When the specific heat capacity of a substance is measured in terms of mass, the atomic or molecular weight of the substance has a significant effect upon the value. For instance, a substance like hydrogen—the lightest of the chemical elements—has a huge specific heat capacity per gram. If the specific heat capacity is measured in terms of molar quantity, the differences between substances is less pronounced and hydrogen’s specific heat capacity is quite unremarkable.

An equation related to Specific Heat Capacity would be: Q = m·c·Δθ

where Q is the heat energy received or given out by the substance, m is the mass of the substance, and Δθ is the change in temperature (in degree Celsius). It could be replaced with ΔT which is in Kelvin (both have same values).

Factors that influence heat capacity measurements

• Temperature: Measuring the heat capacity of water produces different results if the starting point is 20 °C rather than 60 °C. Therefore the temperature at which the measurement was conducted must be specified for the value to be useful.
• Intermolecular forces: Strong intermolecular forces combined with a disordered state (such as hydrogen bonding in liquid water) are likely to increase the heat capacity of a substance. In solid substances, heavy atoms tend to increase heat capacity by making quantum vibration modes more accessible by decreasing their spacing. In the case of an ideal gas, intermolecular forces are absent from the system, thus the specific heat capacity is independent of pressure which forces molecules closer together and to interact more often. Helium behaves much like an ideal gas at standard ambient temperature and pressure
• For a gas, it is necessary to distinguish between specific heat at constant pressure (usually noted $c\_p$) and at constant volume (usually noted $c\_v$). The former, which is also the most commonly used, applies to a gas evolving at constant pressure (such as a gas being heated in a loose bag which allows free expansion), and the latter applies to a gas evolving at constant volume, such as a gas heated in a sealed container which does not change size. Constant pressure heat capacities are always larger for a gas, because heat is absorbed to do the work which is done when the gas expands against external pressure, if it is allowed to do so. *Two analogous distinct capacities can also be defined for liquids and solids. The difference between the two is generally not worth considering at normally encountered conditions since liquids and solids are nearly incompressible at these pressures, so that their thermodynamic behavior is not significantly affected. On the other hand, at very high pressures (such as deep in the Earth) pressures can be high enough to not only change volumes of solids and liquids significantly, but also do a great deal of work with a relatively small change in volume. Here the difference between the two kinds of heat capacities again becomes important.

Table of specific heat capacities