Chemical Reactions, Balancing Equations, and Polyatomic Ions

Vocabulary practice flashcards covering indications of chemical reactions, equation balancing and notation, common monatomic and polyatomic ions, and the four major reaction types.

Chemical Reaction

A process where substances change into new substances with different properties through the breaking and forming of chemical bonds.

Reactants

The starting substances in a chemical reaction that are changed during the process.

Products

The new substances formed after a chemical reaction takes place.

Chemical Formulas

Combinations of chemical symbols and numbers used to represent the kinds and numbers of atoms in a substance.

Chemical Symbols

One- or two-letter abbreviations used to represent chemical elements.

Coefficients

Numbers written before chemical formulas in an equation to balance a reaction and show how many molecules or moles of a substance are involved.

Release of Light or Heat

Evidence of a chemical reaction where energy is produced, causing the reaction to give off light or become hot.

Evolution of Gas

Evidence of a chemical reaction where gas is produced, usually visible as bubbling; common examples include carbon dioxide, hydrogen cyanide, sulfur dioxide, ammonia, and hydrogen sulfide.

Formation of Precipitate

Evidence of a chemical reaction where a solid suddenly forms when two liquids are mixed.

Change in Temperature

Evidence of a chemical reaction in which the substance or reaction mixture becomes warmer (hotter) or colder.

Color Change

Evidence of a chemical reaction in which a substance changes color because a new substance has formed.

Odor Change

Evidence of a chemical reaction in which a new or different smell is produced during the process.

Aqueous Solution $(aq)$

A notation used in chemical equations to denote a substance that is dissolved in water.

Diatomic Elements

Elements that are naturally found in pairs when alone: bromine ($Br_2$), iodine ($I_2$), nitrogen ($N_2$), chlorine ($Cl_2$), hydrogen ($H_2$), oxygen ($O_2$), and fluorine ($F_2$).

Antoine Lavoisier (1743–1794)

The French chemist who proposed the Law of Conservation of Mass by proving that substances are neither lost nor created during a chemical reaction.

Law of Conservation of Mass

A fundamental scientific law stating that the total mass of the reactants equals the total mass of the products; atoms only rearrange during a chemical reaction, while total mass remains the same.

Balancing by Inspection

A trial-and-error method of balancing chemical equations where the number of atoms of each element is equalized by adjusting coefficients.

Pure Elemental Substance Balancing Rule

The guideline in chemical equation balancing stating that pure elemental substances, such as $H_2$, $N_2$, $O_2$, and $Cu$, should be balanced last.

Unchanged Polyatomic Ion Balancing Rule

The guideline stating that if a polyatomic ion remains unchanged on both sides of an equation, it should be treated and balanced as a single whole unit rather than balancing its individual elements.

Ion

An atom that has gained or lost electrons, resulting in a net electric charge.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Monatomic Ion

An ion consisting of a single atom with an electrical charge, such as $Na^+$, $Cl^-$, or $Mg^{2+}$.

Polyatomic Ion

A group of two or more covalently bonded atoms that carries an overall positive or negative charge and acts as a single unit in reactions.

Ammonium ($NH_4^+$)

A polyatomic cation with a charge of $+1$, notable as the only common positive polyatomic ion.

''-ate'' vs. ''-ite'' Rule

A naming rule for polyatomic oxyanions stating that the ''-ate'' ion always contains more oxygen atoms than the ''-ite'' ion (e.g., sulfate $SO_4^{2-}$ has 4 oxygens, while sulfite $SO_3^{2-}$ has 3).

Parentheses Rule

The convention of placing parentheses around a polyatomic ion formula before adding a subscript whenever more than one of that ion is required in a chemical formula (e.g., $Mg(OH)_2$, $Al_2(SO_4)_3$).

Combination Reaction (Synthesis)

A reaction where two or more simple substances (elements or compounds) combine to form a more complex substance, represented generally as $A + B \rightarrow AB$; also known as a direct combination reaction.

Decomposition Reaction

A reaction that is the reverse of a combination reaction, in which a more complex substance breaks down into simpler substances, represented generally as $AB \rightarrow A + B$.

Single Replacement Reaction

A chemical reaction in which an uncombined element replaces another element in a compound, represented generally as $A + BC \rightarrow AC + B$.

Activity Series of Elements

A list of common metals arranged in decreasing order of their ability to replace other metal ions in aqueous solutions, used to determine if single replacement reactions will occur.

Double Replacement Reaction

A reaction in which the reactants exchange anions and cations to form new compounds ($AB + CD \rightarrow AD + CB$); also known as double decomposition, double displacement, or metathesis reaction.