Grade 10 Chemistry Knowledge area Chemical change Physical

Grade 10 Chemistry Knowledge area: Chemical change

Physical and chemical change 1. 1. 2 Chemical change A chemical change results in a new substance being formed, which differs from the original substance(s) in composition as well as in chemical and physical properties. Chemical changes • Types of reactions studied: 1. synthesis reaction: 2. decomposition reaction. Definition

Physical and chemical change • Large amounts of energy are needed to: - break very strong covalent bonds (in molecular substances); - break very strong electrostatic forces (in ionic substances). • Reactions may be, but are not always, reversible reactions.

Physical and chemical change Changes that occur during a chemical change • Chemical composition changes. • Chemical bonds are broken. • Atoms and ions are rearranged. • The initial number of atoms stays the same, but not necessarily the number of molecules. • New chemical bonds are formed. • New substances are formed.

Physical and chemical change Examples 2 Aℓ(s) + 2 Aℓ 6 HCℓ(aq) 6 H 6 Cℓ 2 AℓCℓ 3(aq) + 2 Aℓ 6 Cℓ 3 H 2(g). 6 H

Physical and chemical change Chemical change Molecular substances Forces between atoms (covalent: intramolecular) break. Ionic substances Strong electrostatic forces (ionic bonds) between the ions break. Energy is absorbed. Atoms are rearranged. Ions are rearranged. New molecules form or existing molecules break up. Energy is released. New bonds form. New substance(s) form(s).