Heat The "molar heat capacity" is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the "specific heat capacity", often called simply "specific heat", is the heat capacity per unit mass of a material. Heat capacity is a physical property of a substance, which means that it depends on the state and properties of the substance under consideration. The specific heats of monatomic gases, such as helium, are nearly constant with temperature. Diatomic gases such as hydrogen display some temperature dependence, and triatomic gases (e.g., carbon dioxide) still more. Before the development of the laws of
Gas constant "V" is the volume of gas (SI unit cubic metres), "n" is the amount of gas (SI unit moles), "m" is the mass (SI unit kilograms) contained in "V", and "T" is the thermodynamic temperature (SI unit kelvins). "R" is the molar-weight-specific gas constant, discussed below. The gas constant is expressed in the same physical units as molar entropy and molar heat capacity. From the general equation "PV" = "nRT" we get: where "P" is pressure, "V" is volume, "n" is number of moles of a given substance, and "T" is temperature. As pressure is defined as force per unit