Chemical reaction

High School

Definition

A process in which substances called reactants are transformed into new substances called products by the breaking and forming of chemical bonds. Reactions are often accompanied by signs such as colour change, gas production, or a change in temperature.

Worked examples

\(2\)H\(_2 + \)O\(_2 \)→\( 2\)H\(_2\)O\(\)

Hydrogen and oxygen (reactants) combine to form water (product) by breaking H-H and O=O bonds and forming new H-O bonds.

Mixing baking soda and vinegar produces bubbles of carbon dioxide gas.

The gas production is a visible sign that a chemical reaction is occurring between the reactants.

Iron rusting in moist air forms reddish-brown iron oxide.

The colour change from metallic grey to reddish-brown shows iron has reacted with oxygen to form a new substance.

Common mistakes

Dissolving sugar in water is a chemical reaction → Dissolving sugar is a physical change, not a chemical reaction No new substance forms; the sugar can be recovered by evaporating the water.
The total mass decreases when gas is produced in a reaction → Mass is conserved; the gas still has mass even if it escapes Atoms are rearranged but not created or destroyed, so total mass stays constant.
All reactions produce heat → Some reactions absorb heat (endothermic) while others release it (exothermic) Temperature change can go either direction depending on whether energy is released or absorbed.

Where you'll use it next

Chemical reactions are foundational for studying stoichiometry, reaction rates, equilibrium, and thermochemistry in chemistry, and for understanding metabolism, photosynthesis, and cellular respiration in biology.

Found in 1 StudyPug lesson

Master the Basics of Chemical Reactions

Chemistry 11

Dive into the world of chemical reactions with our engaging video introduction. Understand how atoms rearrange, form new bonds, and create entirely new substances. Build a strong foundation for advanced chemistry concepts.

11th Grade11th