Chemistry 11 Unit Test Notes

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Chemistry 11- Reactions

CHEMISTRY 11-REACTIONS

12-04-02 Unit Test Notes

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Chemistry 11- ReactionsU N I T T E S T N O T E S

Table of Contents

UNDERSTANDING REACTIONS ........................................................................................................................... 1

CHEMICAL REACTIONS ..................................................................................................................................................................... 1

WORD EQUATIONS ............................................................................................................................................. 1

TYPES OF REACTIONS ......................................................................................................................................... 2

COMBUSTION .................................................................................................................................................................................. 2

SYNTHESIS ....................................................................................................................................................................................... 2

DECOMPOSITION............................................................................................................................................................................. 3

SINGLE DISPLACEMENT .................................................................................................................................................................... 3

DOUBLE DISPLACEMENT ................................................................................................................................................................... 4Precipitation Reactions ............................................................................................................................................................ 4

Reactions Producing a Gas ..................................................................................................................................................... 4

Neutralization Reactions ......................................................................................................................................................... 4

BALANCING EQUATIONS .................................................................................................................................... 5

PRACTICAL APPLICATIONS ................................................................................................................................. 5

EXTRACTING METALS ....................................................................................................................................................................... 5

CORROSION AND PROTECTION....................................................................................................................................................... 5

FAMILIAR ALLOYS............................................................................................................................................................................. 5


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Page 1

UNDERSTANDING REACTIONSReactions occur all around us today, whether they are physical or chemical. It is important to

recognize the difference between a physical and a chemical change. The following graphic displays clues

that will result in a chemical reaction.

Chemical Reactions

WORD EQUATIONSOnce we have gathered enough information to prove that the reaction was chemical we must

represent it with an equation, the first step to representing a chemical reaction is writing a word equation.

The word equation consists of the name of the reactants and products. For example,

+ +The equation does not require balancing or the correct chemical formula for the respective

compounds. It is important to make sure that reactants are on the left side, while the products are on the

right side of the arrow.

The products of the reaction will be a different colour than the reactants.Change in Colour

The product of the reactions will change in smell.Change in Odour

The products will be in a gaseous form.Formaiton of Gas

The products will form a solid.Formation of Solid

Energy will be given off as heat .Release or Absorption of Heat


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TYPES OF REACTIONSIdentifying chemical reactions is very simplistic, however it is key to understand reaction before

they occur. This is known as predicting reactions. Reactions can be predicted by their reactants, for

example some reactants will results in a combustion reaction, while some will result in a double

displacement reaction. The following types of reactions are the most common.

Combustion

Combustion reactions are easily recognized by the production of heat energy or a flame.

The reaction can only occur if there are three things present, oxygen gas, a fuel source and heat.

The resultants of this reaction will always be a common oxide of the fuel source compound.

Consider the general form and the example.

+ ! + In the general form AB represents a compound or the fuel source, while AO is a common

oxide of Element A, and BO is a common oxide of element B. Now consider the example.

! + ! ! + !

As displayed in the example, Carbons common oxide is Carbon Dioxide, while

Hydrogens common oxide is DiHydrogen Monoxide. The reactants of the reaction can now be

easily predicted for any combustion reaction. If the fuel source is an element not a compound the

reactants will just be the common oxide of just the element.

Synthesis

Synthesis reactions are the most simple of reactions they take place between two elements

as the reactants. The result of the reaction is the formation of an ionic or molecular compound ofthe two elements. Consider the general form, and the example.

+

In the general form A and B both represent single elements or in case of a HOFBrINCl, the

compound gas. AB represents the compound either ionic or molecular by the reactants. Consider

the example.

! + ! 2

In the example, Oxygen gas, and Nitrogen gas come together to come the molecular

compound Nitrogen Monoxide. In a circumstance where a molecule is to reactant with an elementan synthesis reaction is also possible, however only in certain cases. Consider the example.

2 + ! 2!In the example, Nitrogen Monoxide reacted with more Oxygen gas, to form Nitrogen

Dioxide, this is not a Single Displacement reaction however it is a Synthesis reactions.

Equation not balanced.


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Decomposition

Decomposition reactions works opposite to synthesis reactions, instead of combining two

elements together into a compound, decomposition reaction break after compounds into either

simpler compounds or the element they were formed with. Consider the general form, and the

example.

+

In the general form AB is a compound, and A and B are the elements. Decomposition

reactions require activation energy and do not just occur on their own. Activation energy is the

energy required to allow a reaction to occur consider the following example.

2! !"!#$%&$' 2! + !In this example Water or DiHydrogen Monoxide can be converted into Hydrogen gas and

Oxygen Gas by electricity (activation energy).

Single DisplacementSingle Displacement reactions occur when an element reacts with a compound to replace a

similar type of element within the compound. The condition for this is that the element must have a

lower electronegativity then the one it is replacing. If the replacing element has a higher

electronegativity (i.e. it is lower on the activity series) than the reaction will not occur. Consider the

general form and example.

+ +

In the general form, A and B are like elements, and BC and AC are compounds. Furthermore A is

higher on the activity series (i.e. It has a lower electronegativity) than B. Now consider the example.

Example 1: + 2 2 + ()!

Example 2: +(!)!

In Example 1, Zinc is higher on the activity series thus it could replace Silver in the in the

reaction. Although, in Example 2 Zinc is not higher than Magnesium on the activity series thus no

reaction occurred. An activity series will be provided on the test.


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Double Displacement

A double displacement reaction occurs between two different molecules. In general there

are three types of double displacement reactions. All of which follow the general form.

+ +

Precipitation ReactionsA precipitation reaction occurs when two aqueous solutions react and form a

precipitate and a dissolved solution. In order to figure out which product compound will be

dissolved which will be a solid, the solubility table will be give on the test.

Reactions Producing a Gas

Reactions, which produce a gas will have the reactant of two aqueous solution or a

solid and an aqueous solution.

Neutralization Reactions

Neutralization Reactions occur when a base reacts with an acid. This will always

result in a salt (aqueous) and water.


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BALANCING EQUATIONSBalancing equations is an art, it comes with practice, however the fundamental steps to balance a

chemical equation are exactly the same.

1. Write out the skeleton equation of the reaction that occurred.a.

Ensure your subscripts are correct.b. Ensure you have the right compounds.

()! + ! +!

2. Start balancing the compounds, leave Hydrogen and Oxygen to the end, consider the polyatomicas one if they are on both side, otherwise balance which element.

()! + 2 ! + 2!3. Balance Oxygen and Hydrogen.4. Write the states of the compounds in the reaction.

()!(!) + 2(!") !(!") + 2!(!)PRACTICAL APPLICATIONS

There are many real world applications, which are related to reactions. There are three major

applications of reactions in the industry.

Extracting Metals

Metals with high reactivity are usually found as compounds rather then the pure metal.

When these metals are extracted the ore is combined with and acid. The compound that is formed

by this is then reacted with a more reactive metal. Thus separating the pure metal with was

combined with acid before.

Corrosion and Protection

Corrosion is serious problem for metals in the industry today, for example iron reacts with

atmospheric oxygen to make Iron (III) oxide or rust. To prevent this problem a layer of less

reactive metal is placed on the iron. Additionally it might be coated with a more reactive metal in

which case the reactive metal will react with oxygen and not harm the iron.

Familiar AlloysWe are all accustomed to hearing stainless steel as a popular choice in kitchens. Stainless

steel is an alloy, which is made up of steel and other elements to make it harder and rust free. To

measure the purity of an alloy the Karat system is used. 24 K means that the metal is100% pure

while, 24 K or 14K mean that it is an alloy and not as pure.

Chemistry 11 Unit Test Notes

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