In chemistry, the chemical properties of matter are defined as the characteristics through which the matter changes and transforms into other forms according to the ratio of its components. In physical changes, only the physical state of matter changes, not the structure of its constituent particles. Therefore, changes in all states of matter such as melting, freezing, evaporation, condensation, sublimation and condensation, as well as the dissolution of salts and bases in water, are physical changes.
In chemical changes, the connection of atoms to each other and their electronic arrangement changes in the reactants. Of course, in a chemical reaction, atoms are neither created nor destroyed, and only combination, decomposition or rearrangement takes place. The chemical properties of matter are not visible, but they can be recognized through the five senses. Compared to chemical properties, some physical properties of matter are visible. A chemical change may be accompanied by the release of energy in the form of heat, light, or sound, and may result in gas production, precipitate formation, or color change.
For example, we know gold as a light yellow solid metal that can be turned into a flat sheet or can be twisted and made into a wire. However, the melting point, boiling point, specific heat, heat of vaporization, density and other physical properties of gold are not visible, but these properties can be determined after conducting experiments in the laboratory.
Chemical hazards
Flammable materials
Flammable materials are often in the form of aerosols (fine liquid particles dispersed in the air), gas, liquid or solid. In most laboratories, gases, liquids and solids are more important.
OSHA definition of flammable material
A- Gases that produce a flammable mixture at ambient temperature and pressure with a concentration of 13% (by volume) or less in the presence of air.
B- Gases that produce a flammable mixture at ambient temperature and pressure with a concentration higher than 12 percent by volume in the presence of air.
C- Flammable liquids are liquids whose ignition temperature is lower than 37.8 degrees Celsius (100 degrees Fahrenheit).
T- Flammable solids are materials that catch fire due to explosive factors and explosion caused by friction, moisture absorption and spontaneous change of chemical nature and cause serious hazards.
Using the information in the chemical safety data sheet of a chemical is the best reference to determine their flammability. In addition, their flammability is recorded on the label of such materials.
The things that must be observed when working with flammable materials are:
A- Remove combustible materials from the following places:
1- An environment where direct flame and very hot surfaces (Hot Plate) are used.
2- An environment where unreliable mechanical and electrical devices are working. (due to the possibility of sparking)
B. Flammable materials should be kept in special cabinets. These cabinets should be away from sources of flame and heat or kept in a special place intended for this purpose.
C- In order to prevent the generation of electricity, the floor of the laboratories should be covered with materials that do not produce static electricity. Also, in laboratories that deal with flammable chemicals, if there is a refrigerator or a freezer, it should be confirmed by the relevant specialists that there is no risk of sparks and fire by them.
T- Smoking is prohibited in the laboratory.