What occurs during a chemical change?

During a chemical change, atoms rearrange to form new substances, which is a fundamental characteristic of chemical reactions. In these processes, the bonds between atoms are broken and formed, resulting in the creation of different molecular structures. This means that the original substances, known as reactants, are transformed into entirely new substances, known as products, with distinct chemical and physical properties.

For instance, when hydrogen gas reacts with oxygen gas, water is formed. This transformation involves the rearrangement of hydrogen and oxygen atoms into a new configuration, thus exemplifying how a chemical change manifests through this process of rearrangement.

The other choices describe incorrect interpretations of chemical changes. For instance, the second option may imply simple combinations without a transformational aspect, while the third suggests a loss of mass and energy, which does not occur in chemical changes, as mass is conserved according to the law of conservation of mass. Lastly, the fourth choice indicates that only physical properties change, which undermines the transformative nature of a chemical change where the substances themselves change at the molecular level. Therefore, the accurate option highlights the essence of chemical changes through atom rearrangement.