Chemical Equations & Reactions http://www.unit5.org/chemistry/Equations.html
Feb 12, 2016
Chemical Equations & Reactions
http://www.unit5.org/chemistry/Equations.html
Lecture Outline – Chemical Equations& Reactions
Keys
Lecture Outline – Chemical Equations & Reactions
Lecture Outline – Chemical Equations & Reactions
student notes outlinetextbook questions
http://www.unit5.org/chemistry/Equations.html
textbook questions
text
Chemical Reactions
You should be able to
Classify reactions by type.
Write a balanced molecular equation, complete ionic equation, and a net ionic equation.
Balance oxidation-reduction reactions.
Predict if a precipitate will form using the solubility rules.
Predict products of reactions given the chemical names of thereactants.
Organize Your Thoughts
Chemicalreactions
Chemicalequations
Chemicalequations
• Balancing equations
• Predicting products from reactants
• Synthesis• Decomposition• Single replacement• Double replacement• Combustion
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175
Describing a Chemical Reaction
Indications of a Chemical Reaction
– Evolution of heat, light, and/or sound
– Production of a gas
– Formation of a precipitate
– Color change
Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
change in color change in odor production of newgases or vapor
input or releaseof energy
difficult to reverse
releaseinput
Chemical Equations
Depict the kind of reactantsreactants and productsproducts and their relative amounts in a reaction.
4 Al(s) + 3 O2(g) 2 Al2O3(s)
The numbers in the front are called stoichiometric coefficientsstoichiometric coefficients.
The letters (s), (g), and (l) are the physical states of compounds.
reactantsreactants productproduct
aluminum oxide
Chemical Equations
This equation means:
4 Al(s) + 3 O2(g) 2 Al2O3(s)
4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
4 Al moles + 3 O2 moles yield 2 moles of Al2O3
or
4 g Al + 3 g O2 yield 2 g Al2O3
4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol108 g + 96 g = 204 g
aluminum oxide sandpaper
Chemical Equations
Because the same atoms are present in a reaction at the beginning (reactants)and at the end (products), the amount of matter in a system does not change.
The Law of Conservation of MatterLaw of Conservation of Matter
Kotz web
Chemical Equations
Because of the principle of the conservation of matterconservation of matter,
An equation must be balancedequation must be balanced.
It must have the same number of atoms of the same kind on both sides.
Lavoisier, 1788
Characteristics of Chemical Equations
• The equation must represent known facts.
• The equation must contain the correct formulas for the reactants and products.
• The law of conservation of mass must be satisfied.
Chemical Equations
• Reactants – the substances that exist before a chemical change (or reaction) takes place.
• Products – the new substance(s) that are formed during the chemical changes.
• CHEMICAL EQUATION indicates the reactants and products of a reaction.
REACTANTS PRODUCTS
Word Equations• A WORD EQUATION describes chemical change using
the names of the reactants and products.
Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.
methane + oxygen
Reactant ProductCH4 O2 CO2 H2O+ + 22
carbon dioxide + water
ClCl
ClHH
H
ClClCl
Cl HHHH
H2 + Cl2 HCl H2 + Cl2 2 HCl
reactants products
H Cl
reactants products
H Cl
22
2 22 2
11
(unbalanced) (balanced)
Unbalanced and Balanced Equations
?
Visualizing a Chemical Reaction
Na + Cl2 NaCl
___ mole Cl2 ___ mole NaCl___ mole Na
2
10 5 10
2
10 5 10
Visualizing a Chemical Reaction
Na + Cl2 NaCl 2 2
Meaning of Chemical Formula
Chemical Symbol Meaning Composition
H2O One molecule of water:
Two H atoms and one O atom
2 H2O Two molecules of water:
Four H atoms and two O atoms
H2O2 One molecule of hydrogen peroxide:
Two H atoms and two O atoms
Balancing Chemical Equations
Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product
What is the relationship between conservation of mass andthe fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation?
Determine whether the following equation is balanced.
2 Na + H2O 2 NaOH + H2
2 Na + 2 H2O 2 NaOH + H2
Balancing Chemical Equations
• Write a word equation for the reaction.
• Write the correct formulas for all reactants and products.
• Determine the coefficients that make the equation balance.
Guidelines for Balancing Chemical Equations
1) polyatomic ions first2) even / odd (make all even)
3) H2O Mg(OH)224) single elements last
Example: need 13 oxygen atoms
Multiply by O2 = 13132
“ ”
3X + O2 2Y + Z132
3X + O2 2Y + Z1322
6X + 13 O2 4Y + 2Z
H-OH vs.
?
(NH4)3PO4 + Mg(OH)2 Mg3(PO4)2 NH4OH?
ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxideNH4
1+ OH1-
+ 62 3
Now you try…AlCl3 + Li2CO3 Al2(CO3)3 + LiCl32 6
1) Write a word equation for the reaction.
Write a balanced equation for the reaction between chlorineand sodium bromide to produce bromine and sodium chloride.
2) Write the correct formulas for all reactants and products.
3) Determine the coefficients that make the equation balance.
chlorine + sodium bromide bromine + sodium chloride
Cl2 + NaBr Br2 + NaCl
Cl2 + 2 NaBr Br2 + 2 NaCl
1) Write a word equation for the reaction.
2) Write the correct formulas for all reactants and products.
3) Determine the coefficients that make the equation balance.
aluminum sulfate + calcium chloride calcium sulfate
Al2(SO4)3 + CaCl2 CaSO4 + AlCl3
Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate.
Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3
+ aluminum chloride? ?
CH4 + 2 O2 CO2 + 2 H2O
Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms
Reactants Products
Unbalanced
2 2
catalyst – speeds up reaction
Showing Phases in Chemical Equations
Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s)
Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l)
Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g)
H2O(s) H2O(l) H2O(g)
Additional Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reaction
A reactant or product in the solid state; also used to indicate a precipitate
Alternative to (s), but used only to indicate a precipitate
A reactant or product in the liquid state
A reactant or product in an aqueous solution (dissolved in water)
A reactant or product in the gaseous state
(s)
(l)
(aq)
(g)
Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a gaseous product
Reactants are heated
Pressure at which reaction is carried out, in this case 2 atm
Pressure at which reaction is carried out exceeds normalatmospheric pressure
Temperature at which reaction is carried out, in this case 0 oC
Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction
2 atm
pressure
0 oC
MnO2
Solubility Ionic Equations
Cover the answers, work the problem, then check the answer.
1. Dissolve ammonium nitrate:
2. Precipitate cupric hydroxide:
3. Dissolve chromium thiocyanate:
4. Precipitate lead arsenate:
5. Dissolve silicon permanganate:
6. Precipitate zinc phosphate:
NH4NO3 (s) ---> NH4+1 (aq) + NO3
-1 (aq)
Cu+2 (aq) + 2OH-1 (aq) ---> Cu(OH)2 (s)
Cr(SCN)3 (s) ---> Cr+3 (aq) + 3SCN-1 (aq)
3Pb+2 (aq) + 2AsO4-3 (aq) ---> Pb3(AsO4)2 (s)
Si(MnO4)4 (s) ---> Si+4 (aq) + 4MnO4-1 (aq)
3Zn+2 (aq) + 2PO4-3 (aq) ---> Zn3(PO4)2 (s)