Chemical Reactions & Equations – Key Vocabulary

A set of vocabulary flashcards summarising essential terms from the chapter on Chemical Reactions and Equations.

Chemical Reaction

A process in which one or more substances (reactants) are converted into new substances (products) with different properties.

Reactant

A starting substance that undergoes change during a chemical reaction; written on the left side of a chemical equation.

Product

A substance formed as a result of a chemical reaction; written on the right side of a chemical equation.

Word Equation

A representation of a chemical reaction using the names of reactants and products, e.g., Magnesium + Oxygen → Magnesium oxide.

Chemical Equation

A concise symbolic representation of a chemical reaction using chemical formulae.

Skeletal Equation

An unbalanced chemical equation that shows the correct formulas of reactants and products but unequal numbers of atoms.

Balanced Chemical Equation

An equation in which the number of atoms of each element is the same on both sides, satisfying the law of conservation of mass.

Law of Conservation of Mass

Principle stating that mass is neither created nor destroyed in a chemical reaction; total mass of reactants equals total mass of products.

Hit-and-Trial Method

A technique for balancing equations by adjusting coefficients until atom counts on both sides match using the smallest whole numbers.

Physical-State Symbols

Notations indicating the state of a substance: (s) solid, (l) liquid, (g) gas, (aq) aqueous.

Combination Reaction

A reaction in which two or more reactants combine to form a single product, e.g., CaO + H₂O → Ca(OH)₂.

Decomposition Reaction

A reaction in which a single compound breaks down to form two or more simpler substances.

Thermal Decomposition

Decomposition initiated by heat, such as CaCO₃ → CaO + CO₂ on heating.

Photolytic Decomposition

Breakdown of a compound by light energy, e.g., 2AgCl → 2Ag + Cl₂ in sunlight.

Electrolysis

Decomposition of a substance by passing an electric current through it, as in the electrolysis of water.

Exothermic Reaction

A reaction that releases heat energy to the surroundings.

Endothermic Reaction

A reaction that absorbs energy from the surroundings, usually as heat.

Displacement Reaction

A reaction in which a more reactive element displaces a less reactive element from its compound, e.g., Fe + CuSO₄ → FeSO₄ + Cu.

Double Displacement Reaction

A reaction where two compounds exchange ions to form two new compounds, often producing a precipitate.

Precipitation Reaction

A double displacement reaction that yields an insoluble solid (precipitate) from aqueous solutions.

Oxidation

Process involving gain of oxygen or loss of hydrogen by a substance.

Reduction

Process involving loss of oxygen or gain of hydrogen by a substance.

Redox Reaction

A reaction in which oxidation and reduction occur simultaneously.

Corrosion

Gradual deterioration of a metal by reaction with its environment, such as rusting of iron.

Rancidity

Spoilage of fats and oils due to oxidation, leading to unpleasant taste and odor.

Quick Lime (CaO)

Calcium oxide; produced by heating limestone and used in cement manufacture and whitewashing.

Slaked Lime (Ca(OH)₂)

Calcium hydroxide; formed when quick lime reacts with water, used for whitewashing.

Respiration (Chemical Context)

Exothermic biological oxidation of glucose to release energy: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

Photosynthesis (Equation)

Endothermic process where plants convert CO₂ and H₂O to glucose and O₂ using sunlight and chlorophyll.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed, often written above the reaction arrow.