What is mass in chemistry?

We explain the concept of mass from chemistry and what are its units of measurement. In addition, the difference between weight and mass.

1. What is mass in chemistry?

In chemistry , mass (m) or matter is understood as the amount of matter that a body possesses , or in the case of a chemical reaction , the specific amount of matter comprising each of the reagents involved.

All bodies have a mass, whether they are in a solid , liquid or gaseous state , and said mass is composed of atoms, joined by chemical bonds to form more complex structures. The more atoms in a body, the greater its mass.

In most fields of chemistry, mass is considered as a uniform and constant dimension , although in quantum physics it has been theoretically proven that it is not an absolute value, but that it increases according to the speed of the body, as approaches the speed of light (according to Albert Einstein’s studies and relativity).

On the other hand, according to the chemical approach, the mass never varies during a given reaction, as established by the Mass Conservation Law  (also called the Lomonósov-Lavoisier Law). Thus, the exact amount of matter that was at the beginning of the chemical reaction and that obtained at the end must be exactly the same, although it will be organized differently: some will have changed state, another will have been regrouped into different compounds , etc.

2. Units of measure of mass

The International System of Weights and Measures (SI) proposes the kilogram (kg) as the fundamental unit of mass measurement , together with its secondary units, such as gram, milligram, etc. It is usually measured using scales, both traditional and modern electronic dishes.

There is also the unit of mol ( mol ), used to refer to the amount of substance based on its constituent particles . One mole of any substance, thus, is equivalent to the amount of itself that contains as many elementary units, as there are atoms in twelve grams of carbon-12. Thus,

1 mole = 6.0221429 (30). 10 ²³ elementary units.

This unit is essential for chemistry, since it allows to study the reactions from the proportion of the participating materials, many of which cannot ordinarily be weighed.

3. Difference between mass and weight

Although in common life they are considered more or less synonymous, the mass (m) and the weight (p) are different magnitudes. While the mass refers to the amount of matter, the weight has to do with the intensity with which the matter is attracted by a gravitational field . Therefore, the mass is a more or less absolute dimension, while the weight will vary according to the amount of mass and the distance at which the body is from the origin of gravity .

Similarly, the weight being a force is measured in Newtons (N), unlike the mass, and is measured with a dynamometer , instead of a balance.

For example, an astronaut with his space suit on records a mass of 120 kg and a weight of 1200 N, but after being transported to the Moon, where there is much less gravity, its weight decreases to 200 N, while its mass remains intact .