A process in which substances are transformed into new substances with different properties.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
A chemical change, or chemical reaction, breaks existing chemical bonds and forms new ones, so that atoms are rearranged into new substances with different properties. Clear signs of a reaction include the production of a gas, a colour change, the formation of a precipitate, the release or absorption of heat or light, and the emergence of a new odour. The products cannot be turned back into the original substances by simply reversing the physical conditions. Chemical equations describe these changes by listing reactants and products in balanced form. Combustion, corrosion and digestion are all chemical changes.
Key ideas: A chemical change forms new substances with different formulas by breaking and making bonds. Evidence includes a gas, a precipitate, a color change, a temperature or light change, or an odor, though none is absolute proof. It is written as a balanced equation, and atoms are conserved while molecules are not.
Common mistakes and connections: Color change or bubbles can occur in physical processes (boiling gives bubbles, dissolving CuSO4 gives color), so look for a new substance. Students also assume all chemical changes are irreversible, but many are reversible equilibria. This leads to conservation of mass, stoichiometry and thermochemistry.
In a chemical change colliding particles with enough energy break bonds and form new substances; raising temperature increases such successful collisions. The interactive lesson shows this as a live animation or chart.
Iron rusts to form iron(III) oxide, a new compound that cannot simply be melted back into iron.
A process in which substances are transformed into new substances with different properties.
Chemical Change is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Mixture, Pure Substance, Physical Change.
The next topics in Atomic Structure & Periodicity are Law of Conservation of Mass and Law of Definite Proportions.
Yes. The interactive lesson includes a self-check question on Chemical Change, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Chemical Change is topic 8 of 115 in Atomic Structure & Periodicity.