Chapter 10 – Introduction to Equations

Writing and Balancing Equations Section 10.1

Chemical Reactions

 One or more substances are rearranged to form different substances C 8 H 18 + O 2 -> CO carbon dioxide and water!

2 + H 2 O + ENERGY LOOK, IT’S A HYDROCARBON!!!!! The products are

Indicators of Chemical Reactions  Animation of Experiment (GIF Format, 321 k)      Temperature Change Color Change Odor Production of Gas Bubbles Production of a Precipitate

Representing Chemical Reactions

Symbol

+ -> (s)

Meaning

Separates two or more reactants or products Separates reactants from products Solid state Liquid state (l) (g) (aq) Gaseous state Water solution    Statements called

equations

are used to describe what happens during a chemical reaction

Reactants

equation are the starting substances found on the left side of the

Products

substances formed during a reaction are the

Word Equations and Skeleton Equations

Word Equations

-Lack important information

Skeleton Equations

-Statements that indicate the reactants and products in a rxn -Describe chemical reactions -Uses chemical formulas to identify reactants and products Fe (s) + Cl 2 (g) -> FeCl 3 (s) Iron (s) + chlorine (g) -> iron (III) chloride (s)

equations: 1. hydrogen (g)

Practice Problems

Write skeleton equations for the following word + bromine (g) -> hydrogen bromide (g) H 2 (g) + Br 2 (g) -> HBr (g) 2. carbon monoxide (g) + oxygen (g) -> carbon dioxide (g) CO (g) + O 2 (g) -> CO 2 (g) 3. potassium chlorate (s) -> potassium chloride (s) + oxygen (g) KClO 3 (l) -> KCl (s) + O 2 (g)

Balancing Equations

Chemical Equations also must obey the Law of Conservation of Mass . The number of atoms that are used in the reactants must equal the number of atoms found in the products. Matter can neither be created nor destroyed . A chemical equation that follows the law of conservation of mass is called a balanced chemical equation .

A Chemical Equation H 2 + O 2 -> H 2 0 A Balanced Chemical Equation Coefficient… -> 2 H 2 + O 2 -> 2 H 2 O

Balancing Chemical Equations

1.

2.

3.

4.

5.

There is a procedure for balancing chemical equations: Write the equation (remember your diatomic molecules) Count the atoms of each element Add or adjust the coefficients (subscripts cannot be changed) Reduce coefficients to lowest possible terms Check your work Hydrogen + Chlorine Yields Hydrochloric Acid H 2 + Cl 2 -> HCl

Balancing Equations Practice

Al + O 2 -> Al 2 O 4Al + O 2 -> 2Al 2 O C 3 H 8 + O 2 C 3 H 8 -> CO 2 + 5O 2 + H 2 O -> 3CO 2 + 4H 2 O KNO 3 -> KNO 2 2KNO 3 + O 2 -> 2KNO 2 + 2O 2 O 2 + CS 2 -> CO 3O 2 2 + CS 2 + SO 2 -> CO 2 + 2SO 2