Final answer:
H2 + O2 → H2O + heat represents a chemical change because it involves transforming reactants into a product with new chemical bonds and properties, releasing energy in the process.
Step-by-step explanation:
The reaction H2 + O2 → H2O + heat is an example of a chemical change because it involves the transformation of reactants (hydrogen and oxygen gases) into a different product (water). During this process, the chemical bonds in the reactants are broken, and new bonds are formed to create the product. This kind of change results in the formation of a substance with entirely different properties. The release of heat indicates that the reaction is exothermic, which means energy is released during the formation of new bonds in water molecules.
Burning candle wax and methane are other examples of chemical changes where the structure of the molecules changes, resulting in substances that have different chemical properties from those of the original reactants. Similarly, in the decomposition of hydrogen peroxide, new substances—water and oxygen—are formed via the reorganization of atoms.
The concept of chemical change is important as it signifies a chemical reaction involving energy changes, where bonds are broken and new bonds are formed, and the original substances are converted into different substances with new chemical properties.