Glossary
Acid-base reactions
Chemical reactions involving the transfer of protons (H⁺ ions) from an acid to a base, or the formation of a coordinate covalent bond.
Example:
The reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH) to form salt and water is a common acid-base reaction.
Arrow (→)
A symbol in a chemical equation that indicates the direction of the reaction, pointing from reactants to products.
Example:
In C + O₂ → CO₂, the arrow shows that carbon and oxygen react to form carbon dioxide.
Balancing equations
The process of adjusting coefficients in a chemical equation so that the number of atoms of each element is equal on both the reactant and product sides, adhering to the law of conservation of mass.
Example:
To represent the formation of water, you must use balancing equations to get 2H₂ + O₂ → 2H₂O, ensuring atom count is conserved.
Chemical Change
A change that results in the formation of new substances with different chemical properties and compositions.
Example:
Baking a cake involves a chemical change as ingredients transform into a new substance with different properties.
Coefficients
Numbers placed in front of chemical formulas in a balanced equation, indicating the relative number of moles or molecules of each substance involved in the reaction.
Example:
In 2H₂ + O₂ → 2H₂O, the coefficient '2' in front of H₂O means two molecules of water are formed.
Combustion Reactions
A rapid reaction, often producing heat and light, typically involving a hydrocarbon or organic molecule reacting with oxygen to produce carbon dioxide and water.
Example:
Burning propane (C₃H₈) in a grill is a combustion reaction that releases energy.
Decomposition Reactions
A type of chemical reaction where a single compound breaks down into two or more simpler substances.
Example:
Heating calcium carbonate (CaCO₃) to produce calcium oxide (CaO) and carbon dioxide (CO₂) is a decomposition reaction.
Double Replacement Reactions
A type of chemical reaction where the positive and negative ions of two reacting compounds exchange places to form two new compounds.
Example:
Mixing solutions of silver nitrate and sodium chloride results in a precipitate of silver chloride and sodium nitrate, a classic double replacement reaction.
Formulas
Chemical representations that show the types of atoms and their ratios in a compound or molecule.
Example:
H₂O is the chemical formula for water, indicating two hydrogen atoms and one oxygen atom.
Limiting reactant
The reactant in a chemical reaction that is completely consumed first, thereby determining the maximum amount of product that can be formed.
Example:
If you have 10 hot dogs but only 8 buns, the buns are the limiting reactant for making hot dog meals.
Molar mass
The mass of one mole of a substance, expressed in grams per mole (g/mol), numerically equivalent to the atomic or molecular weight.
Example:
The molar mass of water (H₂O) is approximately 18.02 g/mol, meaning one mole of water weighs 18.02 grams.
Neutralization
A specific type of acid-base reaction where an acid and a base react to form water and a salt, often resulting in a solution with a pH close to 7.
Example:
When you take an antacid for heartburn, it performs a neutralization reaction with stomach acid.
Physical Change
A change that alters the form or appearance of a substance but does not change its chemical composition or identity.
Example:
When you melt an ice cube, it becomes liquid water, but it's still H2O, demonstrating a physical change.
Precipitation
The formation of an insoluble solid (precipitate) from a solution during a chemical reaction, often observed as cloudiness or a solid settling out.
Example:
When lead(II) nitrate and potassium iodide solutions are mixed, a yellow solid of lead(II) iodide forms, which is a precipitation event.
Products
The new substances formed as a result of a chemical reaction, typically written on the right side of a chemical equation.
Example:
When baking soda and vinegar react, the carbon dioxide gas produced is a product.
Reactants
The starting substances in a chemical reaction that undergo transformation, typically written on the left side of a chemical equation.
Example:
In the reaction 2H₂ + O₂ → 2H₂O, hydrogen and oxygen are the reactants.
Redox
Short for reduction-oxidation, these reactions involve the transfer of electrons between chemical species, where one species is oxidized (loses electrons) and another is reduced (gains electrons).
Example:
In a battery, the flow of electrons from one electrode to another is driven by a redox process.
Single Replacement Reactions
A type of chemical reaction where one element replaces another element in a compound.
Example:
When a piece of zinc metal is placed in a copper(II) sulfate solution, the zinc replaces copper, forming zinc sulfate and copper metal, a single replacement reaction.
Solubility rules
A set of guidelines used to predict whether an ionic compound will dissolve in water (be soluble) or form a precipitate (be insoluble).
Example:
According to solubility rules, most chlorides are soluble, but silver chloride (AgCl) is an exception and will precipitate.
Synthesis Reactions
A type of chemical reaction where two or more simple reactants combine to form a single, more complex product.
Example:
The formation of rust (Fe₂O₃) from iron and oxygen is a synthesis reaction.
Titration
A quantitative analytical method used to determine the concentration of an unknown solution (analyte) by reacting it with a solution of known concentration (titrant).
Example:
A chemist might use titration to find the exact concentration of acetic acid in a sample of vinegar.