Chemical Equations

Chemical Equations

Learners can:

• rewrite a chemical reaction as a sentence

• identify the reactants and products of a chemical reaction

Vocabulary: coefficient, product, reactant, yield

Draw

Try your best to make a drawing that represents the Law of Conservation of Mass

Your drawing shouldn't necessarily contain atoms, but it should be an analogy that has similarities to the Law of Conservation of Mass

​What is the point of any math equation?

The answer is not: "To cause misery for 7th grade students"

​How does this relate to the Law of Conservation of Mass?

​Chemists use chemical equations to model the way atoms are rearranged during a chemical reaction. In today's lesson, you will learn:

• the parts of a chemical equation; and

• how to count atoms in a chemical equation.

Anatomy of a Chemical Equation

​Recall that a chemical equation is a model that shows what happens during a chemical reaction. All chemical equations have common characteristics.

• An arrow in the middle of the equation means yield, or produce. The arrow separates the reaction into the substances that enter the reaction and the substances that exit the reaction. An arrow in a chemical equation is similar to an equal sign in a math equation.

• The substances to the left of the arrow are the reactants. A reactant is an element or compound that enters a chemical reaction. There can be one or many reactants in a chemical equation.

• The substances to the right of the arrow are the products. A product is a substance that is produced by a chemical reaction. There can be one or more products in a chemical reaction.

• A plus sign,+, shows that more than one product or reactant is present. A plus sign in a chemical equation works the same way as a plus sign in a math equation.

​Most chemical equations contain numbers. There are two types of numbers commonly found in chemical equations.

• Subscripts are small numbers to the right of and slightly below the element symbol.

• A coefficient is a full-sized number to the left of a symbol or compound. A coefficient tells you how many of the element or compound are present.

​Coefficients and Subscripts

​O₂

​3O₂

Multiple Choice

Which of the formulas contains a coefficient?

• Zn

• 2HCl

• ZnCl₂

• H₂

A coefficient is a number found to the left of an element symbol or compound. A coefficient tells you how many of the element or compound are present, like a coefficient in a math equation tells you how many of a variable are present. Chemists use coefficients to make sure chemical equations follow the law of conservation of mass.

​A chemical equation is like a chemistry sentence. When you read the formulas and symbols from left to right, a chemical equation tells you what happens during a chemical reaction.

Remember the following when you read an equation like a sentence.

• If an element or compound does not have a coefficient, assume that the coefficient is 1.

• A plus sign means and or combines with.

• The arrow means yields or produces.

​You can read the equation as the sentence: One molecule of N2 combines with three molecules of H2 to produce two molecules of NH3.

Multiple Choice

Which sentence correctly describes the equation?

• One unit of Zn₂HCl yields one unit of H₂ZnCl₂.

  
  

• One atom of zinc combines with two units of HCl to yield one molecule of H₂ and one unit of ZnCl₂.

• One unit of zinc yields two units of HCl, two units of hydrogen, and two units of ZnCl.

• One unit of zinc and hydrogen yields two units of HCl and ZnCl₂.

Chemical Reactions Video

Counting Atoms in Equations

​In an upcoming lesson, you will learn how to balance equations. To balance a chemical equation, you will count the number of each atom in both the products and the reactants. Now you will count the number of atoms of each element in each of the substances in the chemical equation:

​What elements are present in this chemical equation?


Periodic Table

Categorize

Options (3)

8

16

4

Match each element to the number of atoms of that element that are found in the formula $$4C_2H_4O$$

Carbon

Hydrogen

Oxygen

​When you find a coefficient before an element or compound, multiply the coefficient by the subscript to find the total number of atoms of each element.

​A balanced chemical equation has equal numbers of atoms of each element in both the reactants and the products.

​Is this balanced?


We will continue with this tomorrow!