SI units and dimensions measurement recommended by the International Union of Pure and Applied Chemistry (IUPAC). In the International unit (SI) system study the seven base physical units and dimensions for measurements, conversion, and analysis. Therefore, we use the base SI unit and dimension data for measurement and conversion of force (newton or dyne), energy (joule or erg), work, heat, etc. But the SI unit of luminous intensity or candela not needed in chemistry learning but it included only for the shake of completeness.
Every physical property has two components, namely, the numerical value and base units. Physical property = numerical value × unit. Thus the quantity 5 Joule means numerical value = 5, and unit = 5 Joule.
International SI Units and Dimensions System
The International unit (SI) system of units and dimensions used for the measurements and study of most of the physical quantities. CGS units broadly use for the measurement of wavelengths or wavenumber. In order to consistency in scientific recording, the international unit system recommended the use of these CGS units. Length, mass, time, electric power, thermodynamics temperature, amount of substance, and luminous intensity are seven base physical quantities and meter, kilogram, ampere, kelvin, mole, and candela are the unit of these quantities.
Ampere is the constant current flowing if maintained in two parallel conductors of infinite length, negligible cross-section, and placed one meter apart in a vacuum. Thus the forces produced between these conductors = 2 × 10-7 newton per meter length.
The fraction of 1/273.16 of the thermodynamic temperature of the triple point of water.
The amount of substance of a system which contains as many elementary particles entities as there are atoms in 0.012 kilograms of carbon-12.
The candela is the unit of luminous intensity, in a given direction of a source that emits monochromatic radiation spectrum of frequency 540 × 1012 hertz. But the radiant intensity in that direction of 1/683 watt per steradian.
Unit Conversion Table in Chemistry
In the below table we use multiple and submultiple prefixes for unit conversion by the roman symbol.
CGS and SI Units and Dimensions of Force
Newton second law of motion,
force = mass × acceleration
∴ Force = (mass × length)/(time)2
Because velocity = length/time
Therefore, the CGS unit of force = gm × (cm/sec2)
= gm cm sec-2 or simply dyne
SI unit of force = Kg × (m/sec2)
= Kg m sec-2 or simply newton
Therefore, the above base unit measurement data provides the dimension of force = [M L T -2].
Force Unit Conversion
1 Newton = (1 kg × 1 m)/(1 sec)2
But 1 kg = 103 gm and 1 m = 102 cm
1 Newton = (103 gm × 102 m)/(1 sec)2
=105 gm cm sec-2
∴ 1 Newton = 105 dyne
Unit and Dimension of Work, Heat or Energy
From the measurement of Work, W = F × S
∴ CGS unit of work = gm cm sec-2 × cm
= gm cm2 sec-2 or simply erg
Measurement of SI unit of work = kg m sec-2 × m
= kg m2 sec-2 or simply joule
From the above measurement of work
= dimension of force × dimension of length
∴ The dimension of work = [M L T-2] × [L]
= [M L2 T-2]
The ability to doing work is termed as energy like kinetic, potential, mechanical, internal, electromagnetic, surface energy, etc. Therefore, measurements of SI units and dimensions of energy and work are the same. Hence the CGS and SI units of work or energy = erg and Joule respectively. Heat is also another form of energy to produce work. But is somewhat different from the other form of energy like chemical or electrical energy. Because all the other forms of energy completely converted into work but heat is not wholly converted into work. Therefore, the unit and dimension of heat and energy are identical.