Science 1206 Chapter 4 - Classifying Compounds and

Chemical Reactions4.1 - Types of Chemical Reactions (pp. 140-153)

Types of Chemical ReactionsIn general, there are 5 major types of chemical reactions:

1) Formation (synthesis) 2) Decomposition3) Single replacement (single displacement)4) Double replacement (double displacement)5) Combustion

Formation reactionsformation reaction - a chemical reaction in which two or more elements combine to produce a compound

Formation reactions - examples1) Sodium and chlorine react to produce sodium chloride

2 Na (s) + Cl2 (g) → 2 NaCl (s)

2) Hydrogen and oxygen react to produce water.

2 H2 (g) + O2 (g) → 2 H2O (l)

Decomposition reactionsdecomposition reaction - a chemical reaction in which a compound breaks down (decomposes) into two or more simpler compounds or elements

Decomposition is essentially the reverse of formation.

Decomposition reactions - examples1) Iron (III) oxide breaks down into iron and oxygen

2 Fe2O3 (s) → 4 Fe (s) + 3 O2 (g)

2) Ammonia decomposes into nitrogen and hydrogen

2 NH3 (g) → N2 (g) + 3 H2 (g)

Single replacement reactionssingle replacement reaction - a chemical reaction in which one element takes the place of another element in a compound

Single replacement reactionsIn the previous diagram, the first equation represents a reaction involving a metal element replacing the metal ion in a compound. The second equation represents a reaction involving a non-metal element replacing the non-metal in a compound.

Ex. 1 Aluminum reacts with a solution of copper (II) chloride to produce copper and aluminum chloride solution.

2 Al (s) + 3 CuCl2 (aq) → 3 Cu (s) + 2 AlCl3 (aq)

Ex. 2 A solution of sodium bromide reacts with chlorine to make sodium chloride solution and bromine.

2 NaBr (aq) + Cl2 (g) → 2 NaCl (aq) + Br2 (l)

Double replacement reactionsdouble replacement reaction - a chemical reaction in which the positive ions of two different compounds exchange places, resulting in the formation of two new compounds

The reactants of a double replacement reaction are often aqueous solutions of ionic compounds.

Double replacement reactions - examples 1) Aqueous solutions of silver nitrate and potassium chromate are mixed,

producing aqueous potassium nitrate and solid silver chromate

2 AgNO3 (aq) + K2CrO4 (aq) → 2 KNO3 (aq) + Ag2CrO4 (s)

2) solutions of copper (I) sulfate and sodium chloride are mixed, making a solution of sodium sulfate and precipitating copper (I) chloride.

Cu2SO4 (aq) + 2 NaCl (aq) → Na2SO4 (aq) + 2 CuCl (s)

Combustion reactionscombustion reaction - a chemical reaction in which a compound or element reacts with oxygen to form compounds called oxides

Another characteristic feature of combustion reactions is that many produce heat and light. The burning of fuels, such as wood, natural gas, and gasoline, to heat buildings and power vehicles involves combustion reactions

For this course, we will deal mainly with hydrocarbon combustion reactions:

CxHy + O2 → CO2 + H2O

In this general equation, CxHy is a general formula for hydrocarbons, with x and y representing integers.

Balancing Hydrocarbon Combustion equations 1. Look at the number of hydrogens in the hydrocarbon compound, and

divide that number by 2.a. If the answer you get is even, you do not need a coefficient in front of the hydrocarbon

formulab. If the answer you get is odd, put the coefficient of 2 in front of the hydrocarbon formula.

2. Balance the carbon atoms first3. Balance the hydrogen atoms next4. Balance the oxygen atoms last, noting on the product side there are

oxygen atoms in both carbon dioxide AND water.

Hydrocarbon combustion - examples1. Octane (C8H18 (l) ) burns in car engines by combining with oxygen,

producing carbon dioxide and water vapour.

2 C8H18 (l) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (g)

2. Methane (CH4 (g)) undergoes combustion.

CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g)

Science 1206 Chapter 4 - Classifying Compounds and

Chemical Reactions4.2 - Acids and Bases (pp.

154-169)

Acids Acid - a chemical that produces hydrogen ions when dissolved in water;a solution with a pH less than 7

The sour taste of edible acids is one distinct physical property of acids. Although some acids are safe to eat as ingredients in food products, such as citric acid and acetic acid, a lot of other acids are not. Many acids are corrosiveand will react with many different substances, including metals.

Acids Another way chemists have defined acids is according to their behaviour in water. This definition was first proposed in 1884 by the Swedish chemist Svanté Arrhenius (1859–1927). Arrhenius defined an acid as a substance that reacts and releases hydrogen ions, H+(aq), in a water solution (or aqueous solution).

Ex. HCl (aq) → H+(aq) + Cl- (aq)

Bases base - a chemical that produces hydroxide ions when dissolved in water; a solution with a pH greater than 7

Bases are bitter-tasting compounds with a slippery feel. The bitterness of basic compounds is responsible in part for the characteristic taste of coffee, tea, and mustard as well the more unpleasant bitterness of many medicines. Bases also have distinct chemical properties, one of which makes them highly corrosive and, therefore, useful in cleaning products.

Bases According to Arrhenius’s definition, a base is a substance that dissolves in water and releases hydroxide ions, OH‒(aq), into the solution.

Ex. sodium hydroxide

NaOH (aq) → Na+ (aq) + OH-

(aq)

Identifying acids and bases Most acidic and basic substances, when dissolved in water, form clear solutions so you cannot distinguish them by looking. Tasting is also not recommended as acids and bases can be corrosive and/or poisonous.

Acid-base indicator - a chemical that is a characteristic colour when in the presence of an acid or base

Litmus paper is a common indicator used to determine the presence of an acid or a base.

An acid will turn blue litmus paper red

A base will turn red litmus paper blue

Litmus paper can only determine the presence of an acid or a base, not a measure of how acidic or basic it is.

The pH scalepH scale - a numerical scale that is used for identifying a solution as acidic, basic, or neutral. The pH value of a solution is a number that expresses the concentration of hydrogen ions, H+

(aq), in the solution.

The pH scale goes from 0 to 14, with acids being less than 7 and bases being greater than 7. Neutral substances have a pH of 7. The lower the pH value, the more acidic the solution and the higher the concentration of hydrogen ions. The higher the pH, the more basic the solution is and the higher the concentration of hydroxide ions.

The pH scaleThe pH scale is a logarithmic scale; every movement of 1 represents a 10-fold concentration difference of hydrogen ions.

Ex. an acid with a pH of 3 has 10 times more hydrogen ions than an acid with a pH of 4, and 100 times more hydrogen ions than an acid with a pH of 5.

Measuring pH There are a few ways to measure pH. One would be universal indicator paper, which turns various colours based on the pH of the substance.

There are also pH probes and meters which accurately display the pH of the substance.

Acids and bases summary

Recognizing acids from chemical names and formulas (table 4.3, p. 160)Binary acids - acids that consist of hydrogen and one other element

Ex. HCl (aq)

Oxoacid - acids that consist of hydrogen, oxygen and another element

Ex. H2SO4 (aq)

Recognizing acids from chemical names and formulas Although acids are molecular compounds, they behave like ionic compounds and hydrogen will form H+ ions when the compound is dissolved in water.

Acids can have both an IUPAC name and a classical name. The IUPAC name is based on the same guidelines you learned to name ionic compounds, with the word “aqueous” at the start of the name. All classical names have the word “acid.”

Recognizing acids from chemical names and formulasWith classical names, here are some clues to recognize if a substance is a binary acid:

• the name begins with hydro-

• the name ends with -ic

Here are some clues to recognize if a substance is an oxoacid:

• the name of the polyatomic ion is included (but without its -ate or -ite ending)

• the name ends with either -ic -or -ous

Recognizing bases from chemical names and formulasSince many bases are ionic compounds composed of metal ions and hydroxide ions, their names and chemical formulas are written following the same IUPAC guidelines you learned for ionic compounds.

Neutralization reactionsneutralization - a chemical reaction between an acid and a base that results in production of a salt and water (HOH)

Ex. Ca(OH)2 (aq) + H2SO4 (aq) → CaSO4 (s) + 2 HOH (l)

A neutralization reactions is a specific case of a double replacement reaction. It is preferable to write water as HOH as it makes balancing the equation easier.

Neutralization reactionsThe water forms as the hydrogen ions of the acid and the hydroxide ions of the base combine. The other ions form a salt—an ionic compound that can be formed during the reaction of an acid and a base.

In most cases (not all) , the salt formed by a neutralization reaction is soluble in water and will not form a precipitate. Whether the acid is added to the base or the base is added to the acid, the removal of both hydrogen ions and hydroxide ions from a solution as they form molecules of water causes the pH of the mixture to approach 7. If the right amounts of acid and base react, the resulting solution will be neutral. This is very important for reactions outide of a lab situation (see fig. 4.15, p. 162)

Neutralizing acids in the environment Rainwater is naturally acidic with a pH of 5.6-5.8 because of the CO2 in the air dissolving in water to form carbonic acid. Similar reactions will occur with nitrous oxides and sulfur oxides to lower the pH even lower, resulting in acid precipitation (see table 4.5, p. 163)

In areas with acidic soil, liming or adding crushed limestone is a technique used to increase the pH of the soil. Limestone is calcium carbonate, and it reacts with the acid to produce water and carbon dioxide and a calcium salt

Ex. H2SO4 (aq) + CaCO3 (s) → CaSO4 (s) + H2O (l) + CO2 (g)

Salts formed from neutralization reactionsDifferent salts have a variety of applications. For example, they are used to make batteries, explosives, and fertilizers. Also, minerals such as calcium, iron, and magnesium are present in multivitamin and mineral tablets as salts. Various salts are also essential parts of cells, tissues, and organs in plants and animals.

Throughout history, table salt has been considered of great value. It was once used to pay wages and wars were fought over control of its trade. Typical sources for table salt are seawater, salt lakes, and rock deposits.

Salts formed from neutralization reactionsAnother commercially important salt is magnesium acetate. Mixtures of magnesium acetate and calcium acetate are used as road salt in the removal of ice from roadways during winter. These salts cause less rusting of vehicles than other de-icing salts, such as calcium chloride and sodium chloride. Also, they are not as damaging to the environment.

Science 1206 Chapter 4 - Classifying Compounds and

Chemical Reactions4.3 - Rates of Chemical Reactions

(pp. 170-177)

Reaction ratereaction rate - the speed at which reactants are converted to products in a chemical reaction

Every chemical reaction proceeds at a definite rate under a specific set of conditions. However, you can speed up or slow down the rate of a chemical reaction by changing those conditions.

Factors that affect reaction rate:

- Temperature- Surface area- Concentration- Presence of a catalyst

Temperature and reaction rateIncreasing temperature, in a lot of cases, will speed up the rate of the reaction. If there is to be a reaction, the particles of the reactant (atoms, molecules, or ions) must come into contact. They must also come into contact with enough energy to allow the reaction to occur. Heating causes the particles of the reactants to move more quickly, resulting in more collisions and more energy. This increases the frequency of collisions that result in reactions.

Surface area and reaction ratesurface area - a measure of how much area of an object is exposed

Increasing the surface area of the reactants causes the reaction to proceed faster.

Ex. crushing a tablet into a powder allows it to react faster; splitting a large junk of wood into smaller pieces allows it to burn faster

With more particles of reactant exposed, the more frequently a collision between reactants that results in a reaction will occur. When fewer particles are exposed, successful collisions between reactant particles become less frequent.

Concentration and reaction rateConcentration means the amount of solute that is dissolved in a certain volume of solution. A higher concentration of one or more reactants increases reaction rate; a lower concentration decreases it.

For products to be formed in a chemical reaction, the reactants must collide with each other with sufficient energy and in the correct orientation. A greater concentration of reactant particles present increases the chance that collisions among reactants will occur. The more collisions there are, the greater the reaction rate.

Catalysts and chemical reactionscatalyst - a substance that increases the rate of a chemical reaction without being used up or changed after the reaction has taken place

Catalysts make some reactions possible and speed other reactions up by lowering the energy needed for them to occur. Energy is needed to break the bonds of reactants in any chemical reaction. One way to increase the rate of a reaction involves lowering the energy needed to break the bonds.

Catalysts and chemical reactionsThere are millions of catalysts—some exist naturally and some are designed and made by people. Your body contains thousands of different biological catalysts, called enzymes. Enzymes are proteins that speed up reactions in living cells. Without enzymes, the reactions would not occur at a fast enough rate to sustain life. Each enzyme in your body is specialized to perform its own function.

Cars have a device called a catalytic converter, used to reduce pollution. It converts carbon monoxide to carbon dioxide and nitrogen oxides into nitrogen gas and oxygen gas by way of metal catalysts like platinum, rhodium, and palladium.