Chemistry: Chemical Reactions and Balancing Equations

Vocabulary flashcards covering chemical reaction types, the Law of Conservation of Mass, rules and procedures for balancing equations, chemical notation, and state symbols.

Law of Conservation of Mass (Matter)

A fundamental scientific law stating that matter cannot be created or destroyed by chemical or physical processes, meaning the matter in the universe is constant and the total mass of the reactants must equal the total mass of the products.

Balanced Chemical Equation

A chemical equation that shows the exact same number of atoms of each element on both sides, dictating the quantity of reactants required and allowing the prediction of product quantities.

Chemical Reaction (Chemical Change)

A process in which chemical bonds between atoms are broken and new bonds are formed to rearrange atoms into new compounds with different properties.

Reactants

Substances present before a chemical reaction takes place, written to the left of the reaction arrow in a chemical equation.

Products

Substances formed from a chemical reaction, written to the right of the reaction arrow in a chemical equation.

Coefficient

A whole number placed in front of a chemical formula to express how many particles or moles of that substance are present in a balanced equation.

Subscript

A number written within a chemical formula indicating the ratio of atoms in a compound, which must never be changed when balancing an equation.

Mole

An amount of a substance that contains exactly $6.02 \times 10^{23}$ particles of that substance.

Balancing Equations by Inspection

A method of balancing chemical equations by counting atoms on each side, adjusting coefficients one element at a time, treating polyatomic ions on both sides as single units, and reducing coefficients to the lowest whole number ratio.

Reaction Arrow ($\rightarrow$)

A symbol indicating a chemical change that is read as "forms", "produces", or "yields", above which reaction conditions such as heat or catalysts are written.

Plus Sign ($$+$)

A symbol placed between multiple substances on the same side of a chemical equation, read as "and", "combines with", or "reacts with".

Solid State Symbol ($(s)$)

A state of matter notation denoting a solid substance, such as powders, filings, crystals, or insoluble precipitates.

Liquid State Symbol ($(l)$)

A rare state of matter notation at standard temperature and pressure (STP), primarily used for substances like $\text{H}_2\text{O}$, $\text{Hg}$, $\text{Br}_2$, certain alcohols, and oils.

Gaseous State Symbol ($(g)$)

A state notation denoting substances in the gas phase, including vapors, steam, smoke, aerosols, or atomized matter.

Aqueous Solution Symbol ($(aq)$)

A state notation indicating that a substance, such as an acid or an ionic compound, is dissolved in water.

Diatomic Elements

Seven specific nonmetal elements that exist in their elemental form as molecules of paired atoms: $\text{H}_2$, $\text{N}_2$, $\text{O}_2$, $\text{F}_2$, $\text{Cl}_2$, $\text{Br}_2$, and $\text{I}_2$.

Word Equation

A chemical equation written entirely in descriptive words naming the reactants and products rather than using chemical symbols.

Formula Equation

A representation of a chemical reaction using chemical formulas, state symbols, and coefficients to depict the reacting substances and products.

Synthesis (Combination) Reaction

A reaction classification in which multiple reactants combine to form a single product, such as $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$.

Decomposition Reaction

A reaction classification in which a single reactant breaks down into multiple products, such as $2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2$.

Single Replacement Reaction

A reaction where a free element displaces a similar element in a compound or where a metal displaces hydrogen from an acid, categorized as anionic, cationic, or metal plus acid.

Double Replacement Reaction

A reaction classification in which two ionic compounds exchange ions to produce two new ionic compounds.

Acid-Base Neutralization

A specific type of reaction between an acid and a base that produces a salt and water, such as $\text{Sr(OH)}_2 + 2\text{HBr} \rightarrow \text{SrBr}_2 + 2\text{H}_2\text{O}$.

Combustion Reaction

A reaction where a substance—typically a hydrocarbon ($\text{C}_x\text{H}_y$)—burns rapidly in oxygen to produce carbon dioxide ($\text{CO}_2$) and water ($\text{H}_2\text{O}$).