Law of Conservation of Mass:
Mass is neither created
nor destroyed during a chemical change. (Strictly speaking there
is no measurable change.)
Law of Conservation of Energy:
Energy is neither created
nor destroyed in chemical processes.
SI (Systéme International) units:
Length: the meter (m) is defined as the distance light travels in a vacuum in 1/299,792,458 sec. (Note that this is truly universal: in principle it can be determined by anyone, anytime, anywhere in the Universe. It also fixes the speed of light, c, as 299,792,458 m/s = 2.99792458 x 108 m sec-1)
Mass: the kilogram (kg) however is still based on the International Prototype Kilogram in Paris and the derived standard kilogram standards held by governments around the world.
Time: the second (s) is defined today as the duration of 9,192,631,770 periods of the radiation of two hyperfine levels of the ground state of the cesium 133 atom.
Amount of substance: the mole (mol) is defined as the number of atoms in 0.012 kg (defined, so sig figs not restricted) of carbon 12 atoms. One mole = 6.022 x 1023 particles.
Temperature: the kelvin (K) is defined as 1/273.15 of the thermodynamic temperature of the triple point of water.
© R A Paselk
Last modified 1 September 2009