Looking at the atomic and molecular level when chemical and physical changes occur can give us insight into the differences between the two. Covalent bonds are bonds where electrons are shared between atoms. Chemical changes occur when covalent bonds are broken and new covalent bonds are formed. During physical changes, covalent bonds are not broken and formed. Please give an example of both and elaborate in your response.
An example of a chemical change is the reaction between iron and oxygen, which creates iron (III) oxide. An example of a physical change is ice melting into water.
Chemical changes involve the breaking and formation of bonds between atoms or molecules, and they create a product which may have different physical properties than any of the reactants. In the reaction between oxygen and iron (a combination reaction), a bond is formed between the gaseous oxygen molecule and the solid iron. This creates a new substance: iron (III) oxide, more commonly known as rust. In combination reactions, new bonds are formed between atoms. In decomposition reactions, such as hydrogen peroxide breaking down into water and oxygen, existing bonds are broken. In displacement reactions, such as photosynthesis, old bonds are broken and new ones are formed.
In contrast, physical changes do not result in a new substance being created, and the atoms remain connected in the same way. For example, when ice is heated, it melts. The solid ice and the liquid water have the same chemical formula—H2O. The only difference is that the physical state of the H2O has changed due to temperature. The bonds present are less rigid in water than they are in ice, but they still hold the same atoms in the same places. Physical changes are often easier to reverse than chemical changes.
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