How are chemical and physical changes different on a molecular level?
Physical changes do not involve molecules.
Chemical changes do not affect bonding between atoms.
Physical changes cause new molecules to form.
Chemical changes involve the breaking of bonds in molecules.
Chemical and physical changes differ on a molecular level in the following ways:
1. Physical changes do not involve molecules: Physical changes typically involve a change in the state or phase of matter, such as freezing, melting, or evaporating. These changes do not alter the chemical composition of the substance, meaning there is no rearrangement of atoms or molecules. For example, when water freezes into ice, the molecules of H2O remain the same, just arranged in a different structure.
2. Chemical changes do not affect bonding between atoms: Chemical changes, on the other hand, involve the rearrangement of atoms and the formation or breaking of chemical bonds. During a chemical change, new substances with different properties are formed. For instance, the combustion of methane (CH4) in the presence of oxygen (O2) produces carbon dioxide (CO2) and water (H2O). In this process, the molecules of methane and oxygen are chemically transformed into the molecules of carbon dioxide and water through the breaking and forming of chemical bonds.
3. Physical changes cause new molecules to form: Physical changes typically do not cause new molecules to form. Instead, they involve changes in the physical properties of substances, such as shape, size, or phase, without altering the chemical composition. An example of a physical change is the cutting of a piece of paper into smaller pieces – no new molecules are formed, only the physical state, size, and shape of the paper are altered.
4. Chemical changes involve the breaking of bonds in molecules: In chemical changes, the breaking and formation of chemical bonds occur. Breaking bonds requires input of energy, while forming bonds releases energy. This process involves the rearrangement of atoms to create new substances with different chemical properties. For example, the digestion of food involves the chemical breakdown of complex molecules into simpler molecules through the breaking of bonds, allowing the body to absorb nutrients.