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.

 

Prefix Symbol Magnitude kilo- k 103 base   100 deci- d 10-1 centi- c 10-2 milli- m 10-3 micro- (or mc) 10-6 nano- n 10-9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dimensional (Unit) Analysis and Problem Solving

For example, how long is a one foot ruler?

 

© R A Paselk

Last modified 1 September 2009