* The chemical properties of a substance are determined by the arrangement of its atoms and the types of bonds between them.

* When two or more substances react, the atoms are rearranged and new bonds are formed, resulting in a new substance with different chemical properties.

* For example, when hydrogen gas (H2) and oxygen gas (O2) react, they form water (H2O). Water has different chemical properties than hydrogen or oxygen, such as the ability to dissolve many substances and to support life.

Physical properties

* The physical properties of a substance are determined by the interactions between its atoms and molecules.

* These interactions include forces such as van der Waals forces, hydrogen bonds, and ionic bonds.

* When two or more substances react, the interactions between the atoms and molecules change, resulting in a new substance with different physical properties.

* For example, when solid sodium (Na) and solid chlorine (Cl2) react, they form sodium chloride (NaCl). NaCl is a white, crystalline solid that is soluble in water, while Na and Cl2 are both gases at room temperature.

**In general, the chemical and physical properties of a substance formed in a reaction are different from the properties of the reactants.

* This is because the reaction changes the arrangement of the atoms and the types of bonds between them.**