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In this lesson, you will learn how chemical equations are used to represent chemical reactions. You will learn that there are many pieces of information provided in a chemical equation, and you will gain an understanding of how to interpret chemical equations.

What’s a Chemical Equation?

A chemical equation is a short-hand way to represent the components of a chemical reaction. There are several pieces of information provided in a chemical equation for those working with the chemical equation or corresponding chemical reaction.

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You’ve worked with equations in mathematics where an equation is used to represent information such as equalities or inequalities. Chemical equations are different from mathematical equations because the two parts of a chemical reaction represent the ‘before’ and ‘after’ of a chemical reaction. In mathematical equations, an equals sign separates the two parts of the equation. In chemical equations, equal signs are not used. Instead, an arrow is used to separate the two sides of the equation, and it points in the direction that a chemical reaction will proceed.

Chemical Equation Analogy

Think of a chemical equation as a mini recipe to make a new substance. To make a beautiful cake, you need to add the correct amounts and proportions of eggs, flour, sugar, oil, and flavorings.

A chemical equation provides information about the correct proportions of ingredients that are needed to make new substances in chemical reactions.Here’s a recipe for making delicious lemonade:

  • To make a large glass of lemonade, use 1 1/2 cups of water plus ; cup of lemon juice plus ; cup of sugar.

Here’s a ”recipe” for the formation of water from molecular hydrogen and molecular oxygen:

  • 1 mole of oxygen plus 2 moles of hydrogen yields 2 moles of water.

Note that just as a cup is a quantity in a recipe, a mole is a quantity in chemical reactions.To write the equation using the chemical symbols and components of a chemical equation, we would write:

Equation that yields water

As you can see, both the chemical equation and the recipe for lemonade provide adequate information that shows how to create a new product.

Parts of a Chemical Equation

In general, we represent an equation in this way:

Basic form of a chemical equation

We say that there are left and right sides of an equation and that they are separated by an arrow. The arrow can be a right-pointing arrow, a left-pointing arrow, or a double-headed arrow, depending on the chemical species and equilibrium involved in the chemical reaction. You can read the arrow as ”goes to,” ”forms” or ”yields.

”To represent a generic chemical equation, we often use alphabetic letters. We read the equation as ”A plus B yields AB” (or ”A plus B forms AB” or ”A plus B goes to AB”). Note that A and B are reactants, and AB is the product (a newly formed substance in a chemical reaction).There are many different kinds of chemical reactions, and they vary in the number of reactants and products. The diagram shows a schematic of the variety of ways reactants and products can change, or rearrange, in a chemical reaction.


Chemical Equations = Reactions

Examples of reactions

Because a chemical equation represents a chemical reaction, it’s important to understand what a chemical reaction is. You observe chemical reactions taking place every day.

A chemical reaction occurs when matter is rearranged to form a different or new substance.Fry an egg – or cook anything really – and a chemical change takes place. The beautiful night sky on the Fourth of July is an amazing display of chemical reactions taking place.

Burning a log in a campfire is an example of a combustion chemical reaction. Even that old rusty screw on the floor of your garage is the result of a chemical reaction having taken place.We say that a chemical change has taken place in a chemical reaction. To help us understand how the matter was rearranged, we use chemical equations to symbolize what chemical changes have taken place.

Atoms ; Molecules in an Equation

As you’ve learned, the main parts of a chemical equation are the reactants and the products.

Besides these, however, there are other pieces of information represented in a chemical reaction. Additional important information provided in chemical reactions involves the number of atoms and molecules in a chemical reaction, shown with coefficients and subscripts.A number in front of a reactant or product is a coefficient and indicates the number of the species required for the chemical reaction to occur. Chemical equations must be balanced, meaning that the same number of atoms entering into a chemical reaction must come out of the chemical reaction.It is the coefficient placed in front of the reactants and products that balance the chemical components of an equation, and you will learn how to balance chemical equations using coefficients in another lesson.

In the following equation, note that there is a 3 in front of molecular hydrogen and a 2 in front of ammonia. When the coefficient of a chemical species is 1 (as is the case with N2), it is not written in the equation, but understood to be 1.

Equation that yields ammonia

A subscripted number is the number of atoms in a particular chemical species. For example, in this chemical equation, the subscripted 2 indicates that 2 atoms of hydrogen make up molecular hydrogen, and there is one atom of nitrogen and 3 atoms of hydrogen in ammonia.Some chemical reactions need a substance to speed up or catalyze a chemical reaction.

Examples of catalysts are heat, electricity, and certain chemicals or metals such as platinum. In a chemical equation, the requirement for a catalyst in the chemical reaction is written above the arrow.Often, it’s important to know the physical state of a reactant or product. These physical states are represented as follows: For a gas, g is shown; a solid is indicated with s; a liquid with an l; and, an aqueous solution by aq. The abbreviations for the physical states of the chemical components in an equation are always italicized.

This diagram summarizes the components in a chemical equation. You’ll want to become familiar with the information provided in a chemical equation and relate it as a recipe for making new chemical substances.

Equation Diagram

Lesson Summary

We learned that a chemical equation is used to show how products form from reactants.

You learned that the reactants are always on the left side of a chemical equation and that the products are always on the right side of the chemical reaction, and that a chemical equation is analogous to a recipe. We also learned that the number of atoms and molecules undergoing a chemical reaction, the physical states of the reactants and products, as well as whether a catalyst is required in the chemical reaction is all information provided in a chemical equation.As you continue in your study of chemistry, you’ll be exposed to many different chemical reactions and their corresponding chemical equations.

You’ll become an expert in interpreting these because you now have an understanding of the components of chemical equations and how they’re represented.

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