Important, measurable quantities or variables, along with their symbols and common units of measurement, are as follows:

• Temperature, T, in degrees centigrade or Celsius (°C), or in Fahrenheit (°F), or in Kelvin units (K).

• Mass, m, in grams (g), or in kilograms (kg) (SI unit).

• Amount, n, measured in moles, one mole being 6.022 xio^{23} particles (e.g., atoms, molecules, or formula units); see Section 1.4.

• Molar Mass, MM, the mass in grams of 6.022 x 10^{23} atoms of an element or molecules of a compound, that is, one mole of a substance; see Section 1.4. The terms molecular weight and formula weight are often used interchangeably with molar mass.

• Avogadro’s Number or Constant: 6.022 x 10^{23} particles or items per mole.

• Volume, V, in cubic centimeters (cm^{3}) or liters (L).

• Pressure, P, in atmospheres (atm), pascal, tore, or psi.

• Density, d, in grams per cubic centimeter (g/cm^{3}) or grams per milliliter (g/mL).

• Concentration may be expressed in any one of several units, depending on the application; see Section 1.7.

Note that amounts of substances are expressed in grams (unit of mass) or moles. Liter is a unit of volume.