Mrs. Sample

Holy Cross Collegiate

Science 24

Science 24

Chapter 3: Types of Chemical Reactions

In this chapter you will learn: How to represent chemical

equations using words and chemical formulas

How to identify and describe different types of reactions

How to recognize chemical formulas for some commonly occurring compounds

Why scientists use balanced chemical equations

How the law of conservation of mass applies to chemical reactions

Starting Point Activity: Flame Test DemoSafety Precautions

What safety precautions must we take in order to perform this lab activity?

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Materials

Sodium nitrate Potassium nitrate Calcium nitrate Copper (II) nitrate

Ethanol Watch glasses Matches

Observations

Chemical Observationssodium nitrate

potassium nitrate

calcium nitrate

copper (II) nitrate

Analysis: Give a possible explanation for what you observed in this demo.

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Mid Unit Review and Preview1. List some types of chemical reactions that you know about right now.

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2. What signs or types of evidence indicate that a chemical reaction has taken place? __________________________________________________________________________________

3. Explain, in your own words, the Law of Conservation of Mass. ___________________________________________________________________________________________________________________________

4. Name and draw the four Hazardous Household Product Symbols (HHPS).

5. Predict what happens in each of the following types of reactions: a. Composition _______________________________b. Decomposition ______________________________c. Combustion _______________________________d. Neutralization ______________________________

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3.1 Word EquationsHere is a summary of what you have learned so far:

Chemical reactions can be simple (ex. ___________________________) or complex (ex. ___________________________).

Chemical changes can be obvious (ex. ___________________________) or less noticeable (ex. ___________________________)

They can occur immediately (ex. ___________________________) or more slowly (ex. ___________________________)

Word equations are a simple way for chemists to describe chemical changes. They also help us recognize patterns that many reactions have in common.

Writing Word EquationsWord equations are always written in the same form:

______________________ ______________________

When there are multiple reactants, or multiple products, we separate them with a (+).

reactant 1 + reactant 2 product 1 + product 2

Some Common Chemical ReactionsExample: In a swimming pool, chlorine and water produce hypochlorous acid.

_________________________ _________________________Example: In a limestone cave, carbonic acid and calcium carbonate produce calcium hydrogen carbonate.

_________________________ _________________________Example: When you cook food on a barbecue, propane and oxygen produce water and carbon dioxide and energy.

_________________________ _________________________Page | 3

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3.2 Types of ReactionsSimple Composition ReactionsIn a simple composition reaction, _______________________ simple -______________ combine to form a __________________. Whenever you see __________________ as reactants, you know that the reaction is a simple composition reaction. The more _______________ there are, the more ________________ the compound is.

Example: The burning of magnesium is a simple composition reaction.

_________________________ _________________________

Example: Hydrogen, oxygen and energy combine to create water.

_________________________ _________________________

Example: Hydrogen and nitrogen combine to create ammonia, a cleaning product.

_________________________ _________________________

In a simple composition reaction, the product is always a compound. If we use the letters A and B to represent two different elements, a simple composition reaction is written in this way:

Most simple composition reactions are _____________________, meaning that some form of energy is ____________________. It is wise to know about this type of chemical reaction before trying it in a laboratory.

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Simple Decomposition ReactionsIn a simple decomposition reaction, a _______________________ breaks down into its more simple parts, ________________. Whenever you see a __________________ as the only reactant, you know that the reaction is a simple decomposition reaction.

Example: During electrolysis, water is broken down into hydrogen gas and oxygen gas. Electric energy is needed to drive this reaction. This makes it an endothermic reaction.

_________________________ _________________________

Example: Potassium chloride is broken down to produce potassium and chlorine gas.

_________________________ _________________________

Example: Hydrochloric acid, over time, can decompose into its elements, hydrogen and chlorine.

_________________________ _________________________

In a simple decomposition reaction, the ______________ are always ______________. If we use the letters A and B to represent two different elements, a simple decomposition reaction is written in this way:

Most decomposition reactions are ____________________, meaning that energy is ____________________. It is useful to know about this type of chemical reaction before trying it in a laboratory.

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Combustion ReactionsAs you have learned, the two necessary _______________ in a combustion reaction are ____________ and _____________.

Example: When you light a candle, the candle wax burns in the presence of oxygen to produce carbon dioxide and water. This is an exothermic reaction.

_________________________ _________________________

Example: Gasoline (octane) in a car engine and oxygen combust to produce carbon dioxide, water vapour, and energy to propel the car. This is an exothermic reaction.

_________________________ _________________________

Example: The same type of reaction occurs when you light a butane lighter. The word equation in this case is:

_________________________ _________________________

Petroleum ProductsOil and natural gas are ___________________. This means that they come from the accumulated remains of _______________ and ________________ from prehistoric times. Fossil fuels form very _______________, which is why many scientists believe we will run out of them. We use them up much more quickly than they can form.

Petroleum products are used for more than fuels. They are also used to create a variety of every day items, including __________________, ___________________, ____________________ and __________________.

Can you name any others?

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Neutralization ReactionsIn Chapter 2, you looked at some everyday chemical reactions, such as taking an antacid to relieve acid indigestion. This is an excellent example of a neutralization reaction. In a neutralization reaction, an acid reacts with a base to produce a form of salt and water. The word equation for a neutralization reaction is:

acid+base→salt compound+water

Example: When you take an antacid, magnesium hydroxide reacts with the hydrochloric acid in your stomach to produce magnesium chloride and water.

_________________________ _________________________

Example: Hydrochloric acid reacts with sodium hydroxide to create water and table salt (sodium chloride).

_________________________ _________________________

Example: When you combine sodium bicarbonate (baking soda) with acetic acid (vinegar), sodium acetate, water and carbon dioxide are produced.

_________________________ _________________________

You may be surprised to know how many neutralization reactions occur all around you every day. They are involved in many natural, household, and industrial products and processes.

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3.3 Formulas for Common CompoundsChemical Names and FormulasWhen you write word equations, you are using the _________________ names for each of the reactants and products. When you look on the _______________________, you will see both the chemical names and ______________________ for each element.

Chemical SymbolsEach element has a unique symbol to identify it. Some chemical symbols consist of one capital letter…

1

H

6

C

7

N

8

O

… and others consist of one capital letter and one lower case letter.

2

He

11

Na

20

Ca

26

Fe

Chemical Formulas and Compound NamesMost chemical compounds are named according to the major _______________ they contain. Information about the chemical composition and structure of a compound is given by its _____________________. For example, the compound _______________________ has the chemical formula ZnS.

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Naming CompoundsThe rule for naming compounds is:

__________________ __________________ idemetal non-metal

Example: ZnS

__________________ __________________metal non-metal

You could now replace the names of the reactants with their chemical symbols, and the product with its chemical formula. When writing formulas, remember to use a subscript to indicate the state of the material. In this example, we are dealing with solids, which are shown as (s). The chemical equation would look like this:

S8 (s)+8 Zn(s)→8 ZnS(s)

Common NamesNot everyone is a scientist, so many chemical compounds are often identified by a common name. These names are easier to use, and they have existed since before the international naming system was created. You already know many chemicals by their common names. As a student of chemistry, you will learn some chemical names. For instance, the common name for sodium chloride is salt. Water is the common name for dihydrogen monoxide.

What’s In a Name?

H 2O(l)

UNIT 1BLM 1–8

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SKILL BUILDER/REINFORCEMENT Periodic Table

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3.4 Chemical EquationsUp to this point, you have observed a number of changes occurring during chemical reactions. These include ________________, ________________, ________________, and ________________. Something that is more difficult to observe is what happens to the ________________ of the ________________ and ________________ in a reaction. This question was explored and answered by a French chemist names Antoine Lavoisier in the 1700’s.

The Law of Conservation of MassLavoisier carefully measured the masses of all the reactants and all the products in a simple decomposition reaction. To his surprise, the total mass of the reactants was exactly equal to the mass of the products.

solid mercury (II) oxide oxygen gas + liquid mercury 10.0 g 0.7 g 9.3 g

Lavoisier concluded that the ____________ in a chemical reaction were just _____________________, not ___________________. This conclusion is known as the Law of Conservation of Mass.

! The Law of Conservation of MassIn a chemical reaction, matter is not created or destroyed. If you start a reaction with 10 g of reactants, you will end up with 10 g of products.

Staying BalancedWhen chemists write chemical equations, they do not usually use word equations. When dealing with chemicals, this method is not exact enough. Consider the following:

energy + wood + concrete + steel + metal house

There clearly isn’t enough information here. Similarly, for chemical equations, we need to record the quantities of each element, and we need to do make sure we have equal numbers of all elements on both sides of the equation.

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