Glossary
Balancing chemical equations
The process of adjusting coefficients in a chemical equation so that the number of atoms for each element is equal on both the reactant and product sides, adhering to the Law of Conservation of Mass.
Example:
To correctly represent the formation of water, one must engage in balancing chemical equations to ensure 2H₂ + O₂ → 2H₂O.
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 the balanced equation 2H₂ + O₂ → 2H₂O, the '2' in front of H₂ and H₂O are coefficients, showing two molecules of each are involved.
Combustion reactions
Chemical reactions that involve a rapid reaction between a substance (often a hydrocarbon) and an oxidant, usually oxygen, producing heat and light. Common products are carbon dioxide and water.
Example:
The burning of propane in a grill, producing CO₂ and H₂O, is a classic example of a combustion reaction.
Decomposition reaction
A type of chemical reaction where a single compound breaks down into two or more simpler substances.
Example:
Heating hydrogen peroxide to produce water and oxygen gas (2H₂O₂ → 2H₂O + O₂) is a typical decomposition reaction.
Hydrocarbon
An organic compound composed solely of hydrogen and carbon atoms. They are commonly used as fuels in combustion reactions.
Example:
Methane (CH₄), the primary component of natural gas, is a simple hydrocarbon.
Law of Conservation of Mass
A fundamental principle stating that matter is neither created nor destroyed in any chemical reaction. The total mass of the reactants must equal the total mass of the products.
Example:
When 10 grams of ice melt into 10 grams of water, the mass remains constant, illustrating the Law of Conservation of Mass.
Reaction mechanisms
The step-by-step sequence of elementary reactions that describe how an overall chemical reaction occurs.
Example:
Understanding the reaction mechanisms of atmospheric pollutants helps scientists predict their impact on ozone depletion.
States of matter (s, l, g, aq)
Abbreviations used in chemical equations to denote the physical state of reactants and products: solid (s), liquid (l), gas (g), and aqueous (aq, dissolved in water).
Example:
In the reaction 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g), the states of matter indicate sodium is solid, water is liquid, sodium hydroxide is aqueous, and hydrogen is a gas.
Stoichiometry
The quantitative study of the relationships between reactants and products in chemical reactions, using balanced equations to calculate amounts of substances.
Example:
Using stoichiometry, a chemist can calculate the exact amount of oxygen gas needed to completely react with a given mass of methane.
Subscripts
Small numbers written below and to the right of an element's symbol in a chemical formula, indicating the number of atoms of that element within one molecule or formula unit.
Example:
In the formula H₂O, the '2' is a subscript, signifying that there are two hydrogen atoms in each water molecule.
Synthesis reaction
A type of chemical reaction where two or more simple substances combine to form a more complex product.
Example:
The formation of ammonia from nitrogen and hydrogen (N₂ + 3H₂ → 2NH₃) is a common industrial synthesis reaction.