Download - Chemical Equations and Reactions
Chemical Equations
and Reactions
Some Definitions Chemical reaction = The process by
which one or more substances are changed into one or more different substances
Chemical equation = Represents a reaction (with symbols and formulas) the identities and relative molecular or molar amounts of the reactants and products in a reaction
Indications of a Chemical Reaction 1.1. Evolution of energy as heat and Evolution of energy as heat and
lightlight
2.2. Production of a gasProduction of a gas
Indications of a Chemical Reaction 3.3. Formation of a precipitateFormation of a precipitate
A solid that is produced as a result of a chemical reaction in solution and that
separates from the solution
4. Color Change4. Color Change
Characteristics of Chemical Equations
1. The equation must represent known facts: all reactants and products must be identified
2. The equation must contain the correct formulas for the reactants and products: use knowledge of writing formulas with oxidation states
Assigning unknown oxidation numbers to multi atom elements
For example: Cr2O72- is Cr = +6 O = -2
Characteristics of Chemical Equations
3. The law of the conservation of mass must be satisfied Balancing equations --- YAY!! Same # of atoms of each element must appear
on each side of a correct chemical equation
*Memorize
symbols on
page 266
Word EquationAn equation which the reactants and
products in a chemical reaction are represented by words
ONLY Qualitative Information Given
Ethane + Oxygen Carbon dioxide + Water
Time to practice writing word equations from a word problem!
Formula EquationAn equation representing the reactants
and products of a chemical reaction by their symbols or formulas (also
including state symbols)ONLY Qualitative Information Given
(Not usually balanced!!)
C2H6 (g) + O2(g) CO2(g) + H2O(l)
WordWord and Formula
Word equationWord equation:
Aluminum + Hydrochloric acid Aluminum chloride + Hydrogen
Formula equation Formula equation (not balanced):
Al(s) + HCl(aq) AlCl3(s) + H2(g)
Correct Chemical EquationBegin with formula equation
Balance using coefficientsNow it is correctly written!!
WrongWrong:Al(s) + HCl(aq) AlCl3(s) + H2(g)
RightRight:2Al(s) + 6HCl(aq) 2AlCl3(s) + 3H2(g)
Balancing Chemical Balancing Chemical EquationsEquations
1. Balance the different types of atoms 1 at a time
2. 1st balance the atoms of elements that are combined and that appear only once on each side of the equation
3. Balance polyatomic ions that appear on both sides of the equation as single units
4. Balance H and O atoms after atoms of all other elements have been balanced
5. Check by final count
Balancing from Word Balancing from Word ProblemProblem
1. 1st figure out the word equation
2. Then write the formula equation from the word equation
3. Balance the equation following the rules from previous slide
PracticePractice: Nitrogen dioxide gas reacts with water to form aqueous nitric acid and
nitrogen monoxide gas.
Significance of a Chemical Significance of a Chemical EquationEquation
1. The coefficient of a chemical reaction indicate relative, not absolute, amount of reactants and products Smallest possible amounts
2. The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients Figure out grams from moles to get total of product
3. The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction
5 Types of Chemical Reactions
1.Synthesis (or Composition)2.Decomposition3.Single-displacement (or
Replacement)4.Double-displacement5.Combustion
Synthesis ReactionsSynthesis Reactions2 or more substances combine
AA(element or compound) + XX (element or compound) AXAX
(Compound) Elements with oxygen and sulfur (forms oxides
and sulfides)
CaO(s) + HH22OO(l) Ca(OH)Ca(OH)22(s)
8Ba(s) + SS88(s) 8BaS8BaS(s)
Metals with Halogens (usually forming ionic compounds)
2K(s) + Cl2(g) 2KCl(s)
Reactions with OxidesOxides of active metals + water =
metal hydroxidesOxides of nonmetals + water =
oxyacids
SynthesisSynthesis ReactionsReactions
Reactants: Zn + IReactants: Zn + I22 Product: Zn IProduct: Zn I22
SynthesisSynthesis ReactionsReactions
Decomposition Decomposition ReactionsReactions
Single compound produces 2 or more simpler
substances
AXAX (Compound) A A(element or compound) + XX (element or
compound)
Decomposition Decomposition ReactionsReactions
Binary Compounds Electrolysis: decomposition by
electric current 2H2O(l) 2H2(g) + O2(g) = LAB!
Carbonates Forming a metal oxide and CO2
Hydroxides Pb(OH)2(s) ----> PbO(s) + H2O(g)
Single-Displacement Reactions
In the case of a positive ion being replaced:
A + BC B + ACOR
In the case of a negative ion being replaced:
A + BC C + BA
For either case we have:element + compound element + compound
Double-Displacement Double-Displacement Reactions Reactions
AB + CD CB + AD
Exchange Partners!Exchange Partners!
Basically:Compound + Compound Compound + Compound
Double-Displacement Double-Displacement Reactions Reactions
Formation of a PrecipitateFormation of a Precipitate
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
Formation of a GasFormation of a Gas
FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)
Formation of WaterFormation of Water
H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)
Double-Displacement Double-Displacement Reactions Reactions
Formation of a PrecipitateFormation of a Precipitate
AgNO3(aq) + KCl(aq) � AgCl� (s) + KNO3(aq)
Combustion Combustion ReactionsReactions
Usually:hydrocarbon + oxygen carbon dioxide and water
Example:Example:
CHCH4(g)4(g) + 2O + 2O2(g)2(g) 2H 2H22OO(g)(g) + + COCO2(g)2(g)
Activity SeriesWhether or not a chemical Whether or not a chemical reaction will really occur!reaction will really occur!
See Handout and/or Page 286 in See Handout and/or Page 286 in your textbook (same thing!)your textbook (same thing!)
Activity Series Practice
11stst can they occur, 2 can they occur, 2ndnd if so write if so write product, then balance:product, then balance:
MgCl2(aq) + Zn(s) NO
Al(s) + H2O(g) Yes (Al2O3(s) + H2(g))