The transformations that take place in materials are classified as chemical and physical.
Physical transformations, although perceptible by the change in the material's appearance, occur more fleetingly, not intimately altering the substance's nature.
The chemical transformations, on the other hand, are so intense that they alter the composition of the material, causing the transformation to produce a chemically different substance from what it had at the beginning.
A physical transformation is different from a chemical transformation because: in a new chemical transformation substances are formed, while physical transformation alters the form of the material, but its composition is the same.
Physical transformations
When we change the size or shape of the material it undergoes a change, but it cannot be changed into another.
Looking microscopically, we see that atoms, ions, or molecules go through an agitation or rearrangement, but they are not altered.
We can see this in the physical state changes.
Notice that:
- Solid: the particles remain in fixed positions, so the volume and shape are well defined.
- Liquid: the particles move more freely and, therefore, the liquid has a specific volume, but its shape varies according to the container.
- Gaseous: the particles move in all directions and with great speed, filling the entire container, so the volume and shape are variable.
The most common example we have for physical transformations is the physical states of water.
When we heat water it vaporizes, if we freeze the water it solidifies, and when we put it at room temperature it returns to a liquid state.
Water in different states has its molecules rearranged, but its composition is the same. So we have a physical transformation.
chemical transformations
New substances are created when matter undergoes a chemical transformation. Reagents are turned into products through reactions.
Reactions cause chemical bonds to be broken or formed, but the atoms that participate in the reaction are the same, only rearranged.
We noticed the occurrence of a chemical transformation due to the appearance of light, the appearance of gas bubbles, formation of solid particles, color change and smell perception.
Let's look at this example:
Sodium is an alkali metal and, as a characteristic of this family, it reacts violently with water.
The reaction between sodium and water generates the metal hydroxide and releases hydrogen gas.
Mixing or chemical transformation?
When we mix two substances, a transformation does not always occur.
For example, when we mix iron and sulfur we get a different color mixture of the substances, if observed separately.
By using a magnet, we were able to attract the iron and separate it from the sulfur, due to its magnetism. That is, we mix the two, but they have not lost their initial properties.
However, if we mix iron and sulfur in a defined proportion of 7g and 4g respectively, and put it under heating, a black colored substance is formed, it is iron II sulfide.
In this way, iron can no longer be separated, as it has been transformed into another substance.
We came to the conclusion that: a mixture is a physical phenomenon, whereas a reaction is a chemical phenomenon.
Physical and chemical phenomena
The transformations that the matter suffers when going through some alteration are also called physical and chemical phenomena.
Let's look at these two examples:
water and sugar
Sugar is a covalent compound and when dissolved in water the molecules disperse but do not change their identity. It is a physical phenomenon.
Water and salt
When we put salt in water, the ions dissociate, as shown by the chemical equation:
As it is an ionic and water-soluble compound, sodium chloride undergoes an alteration, breaking down into its ions. It is a chemical phenomenon.
Cations and anions are solvated when the negative pole of water involves the sodium ions (cations) and the positive pole of water involves the chloride ions (anions).
Both nature and human beings are capable of transforming materials. Naturally, fruit rots and iron rusts. But also, we provoke transformations when we boil water or roast meat. These are examples of material phenomena that we witness in our daily lives.
See too: Physical and chemical phenomena
Quiz - Physical and chemical transformations
Now that you know how to differentiate physical and chemical transformations, test your knowledge in the following quiz:
Take advantage of the following exercises to test your knowledge.:
- Exercises on properties of matter
- Exercises on separation of mixtures
- Exercises on homogeneous and heterogeneous mixtures
