# Equations and constants

Find an online copy of the periodic table at ptable.com.

Useful equations for chemistry:

• Density = mass / volume D = m/V Density can be expressed in grams per cubic centimeter (g/cm3) or kilograms per cubic meter (kg/m3)
• Density of water = 1 g/mL = 1 kg / m3
• Pressure = Force / Area In the SI system force is measured in newtons and area in square meters so pressure is in newtons per square meter, abbreviated as the pascal (Pa). One pascal is one newton per square meter.
• Mass = molar mass x number of moles
• Temperature in kelvin = temperature in celsius + 273 K = C +273

Useful constants for chemistry:

• Avogadro's number = 6.02 x 10^23 Avogadro's number of representative particles (atoms, molecules or formula units) is called a mole of those particles. The relative atomic mass of an element (shown on the periodic table) is the average mass of atoms of that element in amu (see below) but that is also numerically equal to the mass in grams of a mole of atoms of that element.
• Atmospheric pressure at sea level, on average = 101.3 kPa = 760 mm Hg = 1 atmosphere
• STP (standard temperature and pressure) = 0°C and 1 atmosphere (101.3 kPa)
• Molar volume of any gas at STP = 22.4 L
• Elementary charge = charge on a proton = +e = 1.6 x 10^-19 C (the coulomb, C, is the SI unit of charge)
• Charge on an electron = -e = -1.6 x 10^-19 C
• Atomic mass unit (one twelfth the mass of a carbon-12 atom, approximately equal to the mass of a hydrogen-1 atom) = 1 amu = 1.66 x 10^-24 g = 1.66 x 10^-27 kg