Introduction to Chemical Equations Deirdre L Davenport

Chemistry Category 3: Bonding and Chemical Reactions The student will demonstrate an understanding of how atoms form bonds and can quantify the changes that occur during chemical reactions. (C.8) Science concepts. The student can quantify the changes that occur during chemical reactions. The student is expected to (D) use the law of conservation of mass to write and balance chemical equations; and Readiness Standard

Atoms are neither created nor destroyed during any chemical reaction. Chemical changes merely rearrange the atoms. The statement above is supported by: Law of conservation of mass/matter; Law of definite proportions Law of multiple proportions

Basic Information There is the distinction between chemical reactions and chemical equations. A chemical reaction is what really happens. For example, when magnesium burns, a shiny, lustrous piece of flexible metallic ribbon is heated in the presence of a colorless, transparent gas and changes into a white-to-grey, opaque, crumbly, powdery solid. That is a chemical reaction. The chemical equation is a way of representing that reaction by using formulas to represent each of the chemicals involved.

Types of Chemical Equations There are three types of equations with which you need to become familiar: word equations skeleton equations balanced equations

Word Equations The first of the three types of equations are word equations. Word equations are simply a shorthand way of writing down what chemicals were the reactants and products in the chemical reaction. For example magnesium reacts with oxygen to become magnesium oxide: “magnesium + oxygen → magnesium oxide”

Skeleton Equations Skeleton equations, are equations in which we have substituted chemical formulas for the chemical names. Skeleton equations are frequently called unbalanced equations. This skeleton equation shows that magnesium reacts with oxygen to form magnesium oxide “Mg + O 2 → MgO”

Balanced Equations Balanced equation shows how mass is conserved because it shows how atoms are conserved. Balanced equations take into account what substances are involved in the reaction and how much of each is involved in the reaction.

Chemical reactions are represented in a concise way by chemical equations. The reacting substances, called reactants, are located on the left side of the arrow. The substances formed, called products, are located on the right side of the arrow. In a chemical equation, the + sign is read as “react with” and the arrow is read as “produces or yield.”

Numbers in front of the formulas are coefficients, indicating the relative number of molecules or ions of each kind involved in the reaction. Coefficients of 1 are never written - they are understood. Numbers to the lower right of chemical symbols in a formula are subscripts, indicating the specific number of atoms of the element found in the substance. Subscripts are NEVER changed to balance an equation. Subscripts of 1 are never written - they are understood.

As a review... Students can play this SHORT question and answer game “Introduction to Equations” as a review.