Physical and Derived Quantities in Chemistry: SI Units and Many More

In this post, we will learn about the physical and derived quantities in chemistry. We will also understand the difference between weight and mass. Also, Basic terms in chemistry which is used in almost the subject like what is volume, temperature, and density. At last, we will see scientific notations in chemistry.

Physical Quantities

Those quantities that can be measured by physical instruments are known as physical quantities. For Example: Length, Mass, Time, Temperature, Current, Speed, Volume, etc.

Any physical quantity is expressed in two parts-

• Numerical Coefficient like 1, 2, 10
• Units like cm, m, kg

In physical quantities, a unit is the standard of reference chosen to measure any quantity.

Physical Quantities are of two types:

1. Fundamental Quantities
2. Derived Quantities

1. Fundamental or Base Quantities

Those quantities that are independent of other quantities are known as fundamental or base quantities. There are only seven types of fundamental quantities exists.

2. Derived Physical Quantities

Those Quantities which are derived from the base quantities are known as Derived Physical Quantities. For Example: Area, Force, Volume, Speed, Density, etc.

Area = m²
Volume = m³
Speed = m/sec
Density = Kg/M³

Mass and Weight

Mass:- It is the actual amount of substance present in a substance.
Weight:- It is the force exerted by gravity on a substance.

Mass is constant, but weight is variable.
W = mg Where, W = Weight and m = mass

Volume

Volume is the amount of space occupied by a substance. For example: 1 ml = 1 cm³, 1 Litre = 10^-3 m³.

1 litre = 1000 ml
1 litre = 1000 cm³
1 litre = 1000 (10^-2m)³
1 litre = 10³ (10^-6m)
1 litre = 10^-3 m³

Temperature

Temperature is a physical quantity that tells us how hot or cold a substance is.

In simple words, it measures the average kinetic energy (motion) of particles in a substance:

• Higher temperature → particles move faster
• Lower temperature → particles move more slowly

There are 3 common scales to measure temperature:

• Degree Celsius
• Degree Fahrenheit
• Kelvin

Relationship:

K = ^oC + 273.15
^of – 32/9 = ^oC/5

Density

The amount of mass per unit volume is known as density.

Density = Mass/Volume

SI Prefix Table