UNIT 8 – CHEMICAL REACTIONS
REACTIONS AND EQUATIONS (pp. 192 - 200)
1. A ______is simply a chemical change. It is the process by which one or more substances are changed into one or more different substances.
2. The original substances are known as ______while the resulting substances are called ______.
3. Evidence of a chemical reaction can come in the form of things you can see, smell and hear. But, this does not mean a reaction has actually taken place. To verify a reaction has occurred one must analyze the products to verify their physical and chemical properties.
4. Chemical reactions release or absorb energy:
5. Atoms are rearranged in a chemical reaction:
6. Particles must collide for a chemical reaction to occur.
WRITING CHEMICAL EQUATIONS (pp. 200 - 207)
1. Reactions can be described with word equations, but it is more convenient to use chemical symbols and formulas for elements and compounds.
2. A correctly written ______describes exactly which and how many atoms are rearranged during the course of a reaction.
3. Atoms and mass are conserved in chemical reactions.
4. Coefficients written in front of the reactants and products indicate the amounts of each that are present.
5. When trying to write a correct equation, ______change the products or reactants either by adding new ones or by changing the subscripts and identities of the formulas in the equation.
6. A ______is a numeral used in a chemical equation to indicate relative amounts of reactants and products.
7. The process of inserting coefficients to satisfy the law of conservation of mass is referred to as ______.
8. Balancing a formula equation turns it into a chemical equation.
SYMBOLS USED IN CHEMICAL EQUATIONS
1. Chemists make use of symbols to write chemical equations. These are:
WRITING A BALANCED EQUATION
1. Write the word equation, showing all of the reactants and products:
2. Write the correct symbols and formulas for all the reactants and products:
3. Count the number of atoms of each element for both sides of the equation:
4. Insert coefficients for atoms of one element at a time so that the law of conservation of mass is satisfied:
5. Repeat step 4 until the law of conservation of mass holds for all of the elements in the equation.
6. Make sure there are equal numbers of atoms of each element on both sides of the equation.
***** Write balanced equations for the following reactions:
a. Chromium (III) sulfate combines with potassium phosphate to form potassium sulfate and chromium (III) phosphate.
b. Calcium hydroxide and hydrochloric acid react to produce calcium chloride and water.
c. Aluminum sulfate and calcium hydroxide react to produce aluminum hydroxide and calcium sulfate.
***** Balance the following equations:
a. ______NaClO3 (s) → ______NaCl (s) + ______O2 (g)
b. _____ Pb(NO3)2 (aq) + _____ NaCl (aq) → _____ PbCl2 (s) + _____ NaNO3 (aq)
c. _____ C3H8 (l) + _____ O2 (g) → _____ CO2 (g) + _____ H2O (l)
d. _____ Al (s) + _____ Fe2O3 (s) → _____ Al2O3 (s) + _____ Fe (s)
OTHER INFORMATION OBTAINED FROM EQUATIONS
1. In addition to information regarding the physical states of the products and reactants, balanced equations can tell the chemist other things.
2. Reaction conditions are indicated by placing information above and below the arrow:
CLASSIFYING CHEMICAL REACTIONS(pp. 235 - 243)
1. Chemists classify chemical reactions in order to organize the many reactions that occur.
2. Knowing the categories of chemical reactions can help one remember and understand them. It can also help one recognize patterns and predict products.
Synthesis Reactions
1. In this type of reaction, two elements combine to produce a new compound:
2. Two compounds can also combine to form one compound:
3. A compound and an element can combine to form one compound:
Combustion Reaction
1. A reaction between an element or compound and oxygen can be classified as a combustion reaction.
2. In a ______oxygen combines with a substance and releases energy in the form of heat and light.
3. Oxygen appears as a reactant in the form ______.
4. Examples are:
Decomposition Reactions
1. A ______is one in which a simple compound breaks down into two or more elements or new compounds:
2. Decomposition reactions often require an energy source such as heat, light or electricity.
3. Examples:
Single-Replacement Reactions
1. A reaction in which the atoms of one element replace the atoms of another element in a compound is called a ______.
2. It looks like:
3. Another type of single-replacement reaction involves a metal replacing the hydrogens in water:
4. The third type of single-replacement reaction involves a halogen replacing another halogen:
5. Sometimes a metal will not always replace another metal in a compound dissolved in water.
6. This is because metals differ in their reactivities. A metal’s reactivity is its ability to react with another substance.
7. Chemists use an ______to be able to know which metals will replace others during a reaction.
8. The more reactive metals are at the top of the list and the less reactive metals are at the bottom. Metals can replace other metals below them on the list, but not vice versa.
9. The halogens are also represented on this activity series and the same top to bottom rule applies.
Activity Series for Metals and Non-metals
Single Replacement Reactions
Name SymbolMetals
Lithium Li+
Sodium Na+
Potassium K+
Rubidium Rb+
Barium Ba+2
Strontium Sr+2
Calcium Ca+2 / Decreasing activity
↓
reacts with water and acids
Magnesium Mg+2
Aluminum Al+3
Manganese Mn
Zinc Zn+2
Chromium Cr+3
Iron Fe
Cadmium Cd+2
Cobalt Co+2
Nickel Ni+2
Tin Sn
Lead Pb / reacts with acids replacing hydrogen
Hydrogen H2
Antimony Sb
Bismuth Bi
Copper Cu
Mercury Hg
Silver Ag+1
Platinum Pt
Gold Au / fairly unreactive
Non-metals
Fluorine F2
Chlorine Cl2
Bromine Br2
Iodine I2
Double-Replacement Reactions
1. A reaction in which an exchange of ions between two compounds takes place is called a ______.
2. It looks like:
3. The anions have switched places and are now bonded to the other cations in the reaction. The positive and negative ions of two compounds switch places.
4. All double-replacement reactions produce a precipitate, a gas or water.
***** Classify each of the following reactions:
Ti (s) + 2Cl2 (g) → TiCl4 (s)
AgNO3 (aq) + LiI (aq) → AgI (s) + LiNO3 (aq)
2C2H2 (g) + 5O2 (g) → 4CO2 (g) + 2H2O (g)
2H2O2 (aq) → 2H2O (l) + O2 (g)
3Mg (s) + 2Cr(NO3)2 (aq) → 3Mg(NO3)2 (aq) + 2Cr (s)
REACTIONS IN AQUEOUS SOLUTIONS (pp. 214 – 223; pp. 226 - 230)
1. Many reactions involve substances dissolve in water. When a substance dissolves in water, a solution forms. A solution is a homogeneous mixture.
2. A solution contains one or more substances called ______dissolved in water. Water is the ______, the most plentiful substance in the solution.
Aqueous Solutions
1. Although water is always the solvent in aqueous solutions, there are many possible solutes.
2. Some solutes are molecular compounds that exist as molecules in aqueous solutions.
3. Other solutes are molecular compounds that form ions when they dissolve in water.
Reactions That Form Precipitates
1. Some reactions that occur in aqueous solutions produce precipitates.
2. To show the details of reactions that involve ions in aqueous solutions, chemists use ionic equations. Ionic equations are ones in which ions in solution are written as ions in the equation.
3. An ionic equation that shows all of the particles in a solution as they realistically exist is called a ______.
4. Notice that some of the ions are both reactants and products and do not participate in the reaction. Ions that do not participate in a reaction are called ______.
5. Ionic equations that include only the particles that participate in the reaction are called ______.
***** Write chemical, complete ionic and net ionic equations for the following reactions that produce precipitates.
a. Aqueous solutions of potassium iodide and silver nitrate are mixed, forming the precipitate silver iodide and aqueous potassium nitrate.
b. Aqueous solutions of aluminum chloride and sodium hydroxide are mixed, forming the precipitate aluminum hydroxide and aqueous sodium chloride.
c. Aqueous solutions of lithium sulfate and calcium nitrate are mixed, forming the precipitate calcium sulfate and aqueous lithium nitrate.
Reactions That Form Water
1. Some reactions in aqueous solution form water which increases the number of solvent particles.
***** Write chemical, complete ionic and net ionic equations for the reactions between the following substances, which produce water and an aqueous salt:
a. Sulfuric acid and aqueous potassium hydroxide.
b. Nitric acid and aqueous ammonium hydroxide.
c. Phosphoric acid and aqueous magnesium hydroxide.
Reactions That Form Gases
1. A third type of double-replacement reaction that occurs in aqueous solutions results in the formation of a gas.
***** Write chemical, complete ionic and net ionic equations for these reactions.
a. Perchloric acid reacts with aqueous potassium carbonate to produce water, aqueous potassium perchlorate and carbon dioxide gas.
b. Sulfuric acid reacts with aqueous sodium cyanide to produce hydrogen cyanide gas and aqueous sodium sulfate.
c. Nitric acid reacts with aqueous calcium sulfide to produce hydrogen sulfide gas and aqueous calcium nitrate.
OXIDATION – REDUCTION REACTIONS
1. 2 Na (s) + Cl2 (g) → 2 NaCl (s)
2. Both reactants have no charge, they are neutral. NaCl is an ionic compound containing Na+ ions and Cl- ions.
3. Reactions like this one, in which one or more electrons are transferred, are called ______reactions, or ______reactions.
4. Most reactions used for energy production are redox reactions.
Oxidation States
1. The concept of oxidation states provides a way to keep track of electrons in redox reactions.
2. This is particularly useful for redox reactions involving covalent substance.
3. For a covalent bond between two identical atoms, the electrons are split equally between the two.
4. When two different atoms are involved, and the electrons are shared unequally, the electrons are assigned to the atom that has the stronger attraction for the electrons.
5. Oxidation states are assigned according to these rules:
a. An atom in an element is zero.
b. A monatomic ion is the same as its charge.
c. Fluorine is -1 in compounds.
d. Oxygen is usually -2 in compounds except in peroxide (then it is -1).
e. Hydrogen is +1 in its covalent compounds.
6. While uncommon, noninteger oxidation states can exist.
***** Assign oxidation states to all atoms in each of the following compounds:
UO22+
As2O3
HAsO2
Mg2P2O7
Characteristics of Oxidation – Reduction Reactions
1. In some cases the transfer of electrons is very obvious.
2. In other cases the transfer is less obvious.
3. ______is the increase in oxidation state; a loss of electrons.
4. ______is the decrease in oxidation state; a gain of electrons.
***** Identify the substance being oxidized and the substance being reduced.
Cu (s) + 2 Ag+ (aq) → 2 Ag (s) + Cu2+ (aq)
SiCl4 (l) + 2 Mg (s) → 2 MgCl2 (s) + Si (s)
BALANCING OXIDATION – REDUCTION EQUATIONS
1. Difficult to do by simple inspection.
Half – Reaction Method
1. Separate the reaction into two half-reactions, one involving oxidation and one involving reduction.
2. Balance them separately.
3. Add them together.
In Acidic Solution
1. Write separate equations for the oxidation and reduction half-reactions.
2. Balance all the elements except hydrogen and oxygen.
3. Balance oxygen using H2O.
4. Balance hydrogen using H+.
5. Balance the charge using electrons.
6. Multiply one, or both, balanced half-reactions by an integer to equalize the number of electrons transferred in the two half-reactions.
7. Add the half-reactions and cancel identical species.
8. Check that the elements and charges are balanced.
***** Balance the following oxidation-reduction reaction that occurs in acidic solution using the half-reaction method.
Cr2O72- (aq) + Cl- (aq) → Cr3+ (aq) + Cl2 (g)
DIMENSIONAL ANALYSIS (130 - 135)
1.It is a logical approach to problem solving.
2.This technique applies to simple unit conversion problems as well as more complex chemical equations and calculations.
3.These are the steps:
a.Analyze the problem to determine the nature of the answer and its units.
b.Identify the factors that are necessary, either those given in the problem statement or known from previous work.
c.First place the factors containing the DESIRED UNITS of the answer in the proper numerator and/or denominator.
d.Systematically arrange the remaining factors such that all units cancel EXCEPT for the units of the answer.
e.Multiply and divide any numerical coefficients present in the factors and quantities given to obtain a numerical answer to accompany the answer units.
f.Analyze the factors and given quantities to determine the proper number of significant figures for the answer.
g.Inspect the calculated numerical answer to determine if it a REASONABLE answer, that is, if the size of the answer makes sense.
***** A certain person is 172 cm tall. Express this height in decimeters.
***** Convert 1.2L to mL
***** Convert 0.43m to cm.
***** Convert 650g to kg.
***** Calculate the number of meters in 0.200 miles.
***** Convert 0.250 lbs to grams.
***** How long is a 5.0 K race in miles?
***** In a certain part of the country, there is an average of 710 people per square mile and 0.72 telephones per person. What is the average number of telephones in an area of 5.0 km2?
***** The Star of India sapphire weighs 563 carats. What is the weight of the gemstone in grams?
1 carat = 200 mg1 g = 1000 mg
***** An average adult has 5.2 L of blood. What is this volume in gallons?
1 L = 1.057 quarts1 gal = 4 quarts
***** The average mass of a kernel of popcorn is 0.125 g. Determine how many kernels of popcorn are in 0.500 lbs of popcorn.
1 lb = 16.0 oz1 oz = 28.3 g
***** The lethal dose of a certain drug is 1.50 mg/kg of body mass. Determine the lethal dose of the drug needed for a person with a mass of 165 lb.
1 lb = 453.59 g
***** The speed of a migrating loon has been measured to be 14.0 m/s. Determine its speed in mi/hr.
1 mi = 1.6093 km
***** The Toyota Prius, a hybrid electric vehicle, has an EPA gas efficiency rating of 22.0 km/L. What is this rating in mi/gal?
1 mi = 1.6093 km1 gal = 4 qt1 L = 1.0567 qt