Unit 2: Chemical Formulas, Equations, and Reactions

Coefficient

A number in front of a chemical formula in an equation that indicates how many molecules of each reactant and product are involved in a reaction.

Subscript

A number in a chemical formula that tells the number of atoms in a molecule or the ratio of elements in a compound

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yields or produces; indicates a chemical reaction

chemical formula

A combination of chemical symbols and numbers to represent a substance

Chemical equation

a way to describe a chemical reaction using chemical formulas and other symbols

Reactants

A starting material in a chemical reaction

Products

Ending materials in a chemical reaction.

precipitate

A solid that forms from a solution during a chemical reaction.

physical change

A change in a substance that does not change its identity

chemical change

A change in matter that produces one or more new substances

Evidence for a chemical change

production of gas (bubbles), formation of a precipitate, unexpected temperature change, color change, fire, a new product.

open system

A system in which matter can enter from or escape to the surroundings.

closed system

A system in which no matter is allowed to enter or leave

Law of Conservation of Mass

Matter is not created nor destroyed in any chemical or physical change