The third law of thermodynamics states that the entropy of a system will approach a constant value as the temperature approaches absolute zero, such as the entropy is zero at absolute zero (which is -273 degrees Celsius or 0 degrees Kelvin). At absolute zero, the entropy of a pure crystalline substance is zero.
HEAT CAPACITY The heat capacity or thermal capacity is a measurable number that is equal to the ratio of heat added to or removed from a given object to the resulting temperature change. The unit for this is joules per Kelvin (which is the SI unit). The specific heat of an object is the amount of heat necessary to raise an object of one kilogram of mass up 1-degree Kelvin. Heat capacity by itself is considered an “extensive property” of matter because it is directly proportional to the size of the system. If expressing the phenomenon as an “intensive property”, the heat capacity is also divided by the amount of the substance (the mass, number of molecules, or volume). The term “specific” is an intensive property of a substance because it refers to a certain mass of a substance. The specific heat capacity in SI units is Joules per kilogram per degree Kelvin. Water, for example, has a heat capacity of 4.186 joules per gram per degree Celsius. In chemistry, an intensive property of heat is specified relative to a mole of a substance, such as the molar heat capacity, which has the units of joules per mole per degree Celsius. In engineering and other scientific circles, there is the volumetric heat capacity, which is the heat capacity per unit of volume, giving it the units of Joules per cubic meter Kelvin. Calories are sometimes used in place of joules in certain industries. The specific heat capacity in this system is one calorie per kilogram per degree Celsius. There are different ways to measure the heat capacity. It involves adding a known amount of heat to a substance and measuring the change in temperature. This only really works well in the measurement of solids. Gases and liquids are held to a constant pressure or constant volume—most likely constant volume because there is energy necessary in gases to hold them to a constant pressure that interferes with the specific
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