Unit 4: Chemical Reactions

Mr. ChapmanChemistry 20

REVIEWING GRADE 10

Old School Chemistry

In a chemical reaction, substances react with each other to form completely new substances.

There are several common indicators that a person can look at to know that a chemical reaction has occurred.

What is a Chemical Reaction?

Chemical Reactions

1. Heat or light is given off, or heat is absorbed.

2. Colour change

3. A solid is formed

4. A gas is formed

5. The change is difficult to reverse

Indicators of a Chemical Reaction

Observe the two examples of a chemical reaction.

The first chemical reaction is between barium hydroxide and ammonium thiocyanate.

The second reaction is between sucrose and sulfuric acid.

Record your observations after watching the reactions. How many indicators of reactions did you see?

Examples:

A word equation is one way of representing a chemical reaction. A word equation tells you what reacts and what is produced.

Word equations allow chemists to recognize patterns, and to predict what the products of a chemical reaction might be.

Word equations are written in a specific format.

Word Equations

The left side of the equation represents all of the reactants. The reactants are the chemicals that combine to form a new substance.

The right side of the equation contains all of the products. The products are the result of the chemical reaction.

An arrow points from the reactants to the products.

Word Equation Format

First Reaction

Barium hydroxide + Ammonium thiocyanate

Ammonia gas + Water + Barium thiocyanate

Second Reaction

Sucrose + Sulfuric acid Carbon + Water

Word Equations from Examples

Notice that ALL reactants and products are separated by plus signs. We never write a minus sign in an equation, it does not make any sense in chemistry.

All the reactants All the products

reactant 1 + reactant 2 product 1 + product 2

Word Equations

1. Iron reacts with oxygen in the air to form rust, also known as iron (III) oxide. Write a word equation that represents this change.

2. Copper is placed in a beaker of silver nitrate, forming silver metal and copper(II) nitrate. Write a word equation that represents this change.

3. Hydrogen is produced when zinc metal and hydrochloric acid react with each other, and zinc chloride is also formed. Write a word equation that represents this change.

Examples:

Skeleton equations are also used to represent chemical reactions, but instead of using words to present the chemicals, the formulas are used.

Word Equation: hydrogen + oxygen water

Skeleton Equation: H2 + O2 H2O

Skeleton Equations

If you understand how to write a word equation, you can most definitely write a skeleton equation.

Just a couple of notes: The formula of a metal is just the symbol

for that metal. For example, if sodium reacts with water, the formula for sodium is Na.

Remember about the diatomic elements. For example, when oxygen is written as a reactant or product, its formula is O2.

Skeleton Equations

1. Sodium reacts with chlorine to form sodium chloride2. Copper and water are formed when copper (II) oxide reacts

with hydrogen3. Hydrogen and chlorine react to form hydrochloric acid (HCl)4. Lead and sulfur dioxide are formed when lead (II) sulfide

and oxygen react.5. The product of a reaction between aluminum metal and

bromine is aluminum bromide.6. Hydrogen sulfide decomposes to form hydrogen and sulfur

(the formula for sulfur is S8).

7. Lead (II) nitrate and potassium iodide combine to form lead (II) iodide and potassium nitrate.

8. Carbon monoxide and oxygen react to produce carbon dioxide.

9. Hydrogen gas and calcium hydroxide are produced when calcium reacts with water.

Write Some Word & Skeleton Equations