Unit A: Matter and Chemical Change Science 24 Mrs. Sample

3.1 Word Equations

What You’ve Learned So Far:  Chemical reactions can be simple (like powering a space shuttle) or complex (like taking an antacid)  Chemical changes can be obvious (like burning a candle) or less noticeable (like the reaction that makes a cake rise)  They can occur immediately (like explosives) or more slowly (like the ripening of a banana)

Writing Word Equations Word equations are always written in the same format:  The left side of the equation lists all the reactants  The right side of the equation lists all the products  An arrow points from the reactants to the products. It shows that something is produced during the reaction. all reactants  all products

Writing Word Equations  All the reactants and all the products in a word equation are separated by a plus sign reactant 1 + reactant 2  product 1 + product 2

3.2 Types of Reactions zeheZh5Es&list=UUPMnnlWR9-NB_Uk5RTGkIXA

Types of Reactions  There are four main types of reactions that we will study in this section. You have already learned about two of them.  Simple composition  Simple decomposition  Combustion  Neutralization

Simple Composition Reactions  In a simple composition reaction, two or more simple elements combine to form a compound. Whenever you see two elements as reactants, you know that the reaction is a simple composition reaction. The more elements there are, the more complex the compound is.

Example  The burning of magnesium is a simple composition reactionburning of magnesium  magnesium + oxygen  magnesium oxide

Simple Composition Reactions  Most simple composition reactions are exothermic, meaning that some form of energy is released. It is wise to know about this type of chemical reaction before trying it in a laboratory.

Simple Decomposition Reactions  In a simple decomposition reaction, a compound breaks down into its more simple parts, elements. Whenever you see a compound 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.electrolysis  water + energy  hydrogen gas + oxygen gas

Simple Decomposition Reactions  Most decomposition reactions are endothermic, meaning that energy is absorbed.  It is useful to know about this type of chemical reaction before trying it in a laboratory.

Predicting Products  Please work through “Predicting Products” (workbooks page 7/8) independently.  For more background on Sir Humphry Davy, read page 45 of your textbook.

Combustion Reactions  As you have learned, the two necessary reactants in a combustion reaction are oxygen and fuel.

Petroleum Products  Oil and natural gas are fossil fuels. This means that they come from the accumulated remains of plants and animals from prehistoric times.  Fossil fuels form very slowly, 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  Petroleum products are used for more than fuels. They are also used to create a variety of everyday items, including synthetic fibres, cosmetics and tires.

Did You Know?  76 L of petroleum can provide the gasoline to drive a vehicle 485 km, or it can produce 24 shirts, 5 m 2 of carpeting material, 2 car tires, 30 m of 1.3 cm diameter rope, 12 windbreakers, 2 tents, 4 sleeping bags, 6 duffel bags, 1 blanket, 4 sweaters, and 15 parkas!

Neutralization Reactions  In a neutralization reaction, an acid reacts with a base to produce a form of salt and water.

3.3 Formulas for Common Compounds

Chemical Names and Formulas  When you write word equations, you are using the chemical names for each of the reactants and products.  When you look on the periodic table, you will see both the chemical names and chemical symbols for each element.

Chemical Symbols  Each element has a unique symbol to identify it. Some chemical symbols consist of one capital letter, and others consist of one capital letter and one lower case letter.

Compound Names  Most chemical compounds are named according to the major elements they contain.  Information about the chemical composition and structure of a compound is given by its chemical formula.  For example, the compound zinc sulfide has the chemical formula ZnS.

Naming Compounds  The rule for naming compounds is: ________________ ____________ide metal non-metal Example: ZnS zinc sulfide

Naming Compounds  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.  (s) – the material is in solid state  (l) – the material is in liquid state  (g) – the material is in gas state  (aq) – the material is in solution

Common Names  Many chemical compounds are often identified by a common name. These names are  Easier to use  Older – they existed before the chemical naming system was created.  Examples:  sodium chloride (salt)  dihydrogen monoxide (water)  nitrous oxide (laughing gas)  Other examples?

The Pieces of a Chemical Formula

Some Common Chemicals  Choose five compounds from this list.  Identify the chemical symbols present in each compound, and write down the names of the elements present.

Chemical Names and Formulas  If the chemical name is given, write down the chemical formula.  If the chemical formula is given, write down the chemical name.  Use your periodic table to help you!

3.4 Chemical Equations

Chemical Equations  Up to this point, you have observed a number of changes occurring during chemical reactions. These include:  Colour changes  Odour changes  Energy changes  Gas bubbles formed  Precipitate formed

Chemical Equations Something that is more difficult to observe is what happens to the masses of the reactants and products in a reaction. This question was explored and answered by a French chemist named Antione Lavoisier in the 1700s.

Antoine Lavoisier Lavoisier 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

The Law of Conservation of Mass  Lavoisier concluded that the atoms in a chemical reaction were just rearranged, not destroyed. This conclusion is known as the Law of Conservation of Mass.

The Law of Conservation of Mass In a chemical reaction, matter is not created or destroyed.

Staying Balanced  When chemists write chemical equations, they do not usually use word equations.  When dealing with chemicals, this method is not exact enough.

How to Build a House 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 make sure we have equal numbers of all elements on both sides of the equation.

Balancing Chemical Equations  do.edu/en/simulati on/balancing- chemical- equations do.edu/en/simulati on/balancing- chemical- equations