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2. Experiencing Chemical Change. chemical reactions are happening both around you and in you all the timesome are very simple, others are complexin terms of the pieces ? even the simple ones have a lot of interesting principles to learn fromchemical reactions involve changes in the structures of the molecules, and many times we can experience the effects of those changesWhat are some examples of chemical reactions you experience?.
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1. Chapter 7ChemicalReactions
2. 2 Experiencing Chemical Change chemical reactions are happening both around you and in you all the time
some are very simple, others are complex
in terms of the pieces – even the simple ones have a lot of interesting principles to learn from
chemical reactions involve changes in the structures of the molecules, and many times we can experience the effects of those changes
What are some examples of chemical reactions you experience?
3. 3 Chemical Reactions Reactions involve chemical changes in matter resulting in new substances
Reactions involve rearrangement and exchange of atoms to produce new molecules
Elements are not transmuted during a reaction
4. 4 Evidence of Chemical Reactions look for evidence of a new substance
visual clues (permanent)
color change
precipitate formation
solid that forms when liquid solutions are mixed
gas bubbles
large energy changes
container becomes very hot or cold
emission of light
other clues
new odor
whooshing sound from a tube
permanent new state
5. 5 Evidence of Chemical Change
6. 6 Evidence of Chemical Change in order to be absolutely sure that a chemical reaction has taken place, you need to go down to the molecular level and analyze the structures of the molecules at the beginning and end
7. 7 Chemical Equations Shorthand way of describing a reaction
Provides information about the reaction
Formulas of reactants and products
States of reactants and products
Relative numbers of reactant and product molecules that are required
Can be used to determine weights of reactants used and products that can be made
8. 8 Conservation of Mass Matter cannot be created or destroyed
Therefore the total mass cannot change
and the total mass of the reactants will be the same as the total mass of the products
In a chemical reaction, all the atoms present at the beginning are still present at the end
if all the atoms are still there, then the mass will not change
9. 9 The Combustion of Methane methane gas burns to produce carbon dioxide gas and gaseous water
whenever something burns it combines with O2(g)
10. 10 Combustion of Methane methane gas burns to produce carbon dioxide gas and gaseous water
whenever something burns it combines with O2(g)
CH4(g) + O2(g) ® CO2(g) + H2O(g)
11. 11 Combustion of MethaneBalanced to show the reaction obeys the Law of Conservation of Mass it must be balanced
CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)
12. 12 Chemical Equations CH4 and O2 are the reactants, and CO2 and H2O are the products
the (g) after the formulas tells us the state of the chemical
the number in front of each substance tells us the numbers of those molecules in the reaction
called the coefficients
13. 13 Chemical Equations this equation is balanced, meaning that there are equal numbers of atoms of each element on the reactant and product sides
to obtain the number of atoms of an element, multiply the subscript by the coefficient
1 ? C ? 1
4 ? H ? 4
4 ? O ? 2 + 2
14. 14 Symbols Used in Equations symbols used to indicate state after chemical
(g) = gas; (l) = liquid; (s) = solid
(aq) = aqueous = dissolved in water
energy symbols used above the arrow for decomposition reactions
D = heat
hn = light
shock = mechanical
elec = electrical
15. 15 Writing Balanced Chemical Equations Write a skeletal equation by writing the formula of each reactant and product
Count the number of atoms of each element on each side of the equation
polyatomic ions may often be counted as if they are one “element”
Pick an element to balance
if an element is found in only one compound on both sides, balance it first
leave elements that are free elements somewhere in the equation until last
16. 16 Writing Balanced Chemical Equations Find the Least Common Multiple of the number of atoms on each side
the LCM of 3 and 2 is 6
Multiply each count by a factor to make it equal to the LCM
Use this factor as a coefficient in the equation
if there is already a coefficient there, multiply it by the factor
it must go in front of entire molecules, not between atoms within a molecule
Recount and Repeat until Balanced
17. 17 Examples when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
Mg(s) + O2(g) ® MgO(s)
18. 18 Examples Under appropriate conditions at 1000°C ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water
NH3(g) + O2(g) ® NO(g) + H2O(g)
19. 19 Aqueous Solutions Many times, the chemicals we are reacting together are dissolved in water
mixtures of a chemical dissolved in water are called aqueous solutions
Dissolving the chemicals in water helps them to react together faster
the water separates the chemicals into individual molecules or ions
the separate, free floating particles come in contact more frequently so the reaction speeds up
20. 20 Predicting Whether a Reaction Will Occur in Aqueous Solution “forces” that drive a reaction
formation of a solid
formation of water
formation of a gas
transfer of electrons
when chemicals (dissolved in water) are mixed and one of these 4 things can occur, the reaction will generally happen
21. 21 Dissociation when ionic compounds dissolve in water, the anions and cations are separated from each other - this is called dissociation
however not all ionic compounds are soluble in water!
when compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion
22. 22 Dissociation potassium iodide dissociates in water into potassium cations and iodide anions
KI(aq) ? K+1(aq) + I-1(aq)
copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions
CuSO4(aq) ? Cu+2(aq) + SO4-2(aq)
23. 23 Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions
K2SO4(aq) ? 2 K+1(aq) + SO4-2(aq)
24. 24 Electrolytes electrolytes are substances whose water solution is a conductor of electricity
all electrolyte have ions dissolved in water
25. 25 Electrolytes in strong electrolytes, all the electrolyte molecules or formula units are separated into ions
in weak electrolytes, a small percentage of the molecules are separated into ions
in nonelectrolytes, none of the molecules are separated into ions
26. 26 Types of Electrolytes salts = water soluble ionic compounds
all strong electrolytes
acids = form H+1 ions in water solution
sour taste
react and dissolve many metals
strong acid = strong electrolyte, weak acid = weak electrolyte
bases = water soluble metal hydroxides
bitter taste, slippery (soapy) feeling solutions
increases the OH-1 concentration
27. 27 When will a Salt Dissolve? a compound is soluble in a liquid if it dissolves in that liquid
NaCl is soluble in water, but AgCl is not
a compound is insoluble if a significant amount does not dissolve in that liquid
AgCl is insoluble in water
though there is a very small amount dissolved, but not enough to be significant
28. 28 When will a Salt Dissolve? Predicting whether a compound will dissolve in water is not easy
The best way to do it is to do some experiments to test whether a compound will dissolve in water, then develop some rules based on those experimental results
we call this method the empirical method
29. 29 Solubility RulesCompounds that are Generally Soluble in Water
30. 30 Solubility RulesCompounds that are Generally Insoluble
31. 31 Using the Solubility Rules to Predict an Ionic Compound’s Solubility in Water first check the cation, if it is Li+, Na+, K+, or NH4+ then the compound will be soluble in water
regardless of the anion!
if the cation is not Li+, Na+, K+, or NH4+ then follow the rule for the anion
if a rule says the compounds are mostly soluble, then the exceptions are insoluble
but if a rule says the compounds are mostly insoluble, then the exceptions are soluble
note: slightly soluble ? insoluble
32. 32 Determine if Each of the Following is Soluble in Water KOH
AgBr
CaCl2
Pb(NO3)2
PbSO4
33. 33 Determine if Each of the Following is Soluble in Water KOH Soluble, because the cation is K+
AgBr Insoluble, even though most compounds with Br- are soluble, this is an exception
CaCl2 Soluble, most compounds with Cl- are soluble
Pb(NO3)2 Soluble, because the anion is NO3-
PbSO4 Insoluble, even though most compounds with SO42- are soluble, this is an exception
34. 34 Precipitation Reactions many reactions are done by mixing aqueous solutions of electrolytes together
when this is done, often a reaction will take place from the cations and anions in the two solutions exchanging
if the ion exchange results in forming a compound that is insoluble in water, it will come out of solution as a precipitate
35. 35 Precipitation Reactions
36. 36 Precipitation Reactions
37. 37 No Precipitate Formation = No Reaction
38. 38 Process for Predicting the Products ofa Precipitation Reaction Determine what ions each aqueous reactant has
Exchange Ions
(+) ion from one reactant with (-) ion from other
Balance Charges of combined ions to get formula of each product
Balance the Equation
count atoms
Determine Solubility of Each Product in Water
use the Solubility Rules
if product is insoluble or slightly soluble, it will precipitate
if neither product will precipitate, no reaction
39. 39 Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms Write the formulas of the reactants
Na2CO3(aq) + CuCl2(aq) ?
Determine the ions present when each reactant dissociates
(Na+ + CO32-) + (Cu+2 + Cl-) ?
Exchange the Ions
(Na+ + CO32-) + (Cu+2 + Cl-) ? (Na+ + Cl-) + (Cu+2 + CO32-)
40. 40 Write the formulas of the products
cross charges and reduce
Na2CO3(aq) + CuCl2(aq) ? NaCl + CuCO3
Balance the Equation
Na2CO3(aq) + CuCl2(aq) ? 2 NaCl + CuCO3
Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms
41. 41 Determine the solubility of each product
NaCl is soluble
CuCO3 is insoluble
Write an (s) after the insoluble products and a (aq) after the soluble products
Na2CO3(aq) + CuCl2(aq) ? 2 NaCl(aq) + CuCO3(s) Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms
42. 42 Ionic Equations equations which describe the chemicals put into the water and the product molecules are called molecular equations
2 KOH(aq) + Mg(NO3)2(aq) ® 2 KNO3(aq) + Mg(OH)2(s)
equations which describe the actual dissolved species are called ionic equations
aqueous electrolytes are written as ions
soluble salts, strong acids, strong bases
insoluble substances and nonelectrolytes written in molecule form
solids, liquids and gases are not dissolved, therefore molecule form
2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) ® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)
43. 43 Ionic Equations ions that are both reactants and products are called spectator ions
2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) ® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)
44. 44 Acid-Base Reactions also called neutralization reactions because the acid and base neutralize each others properties
in the reaction of an acid with a base, the H+1 from the acid combines with the OH-1 from the base to make water
the cation from the base combines with the anion from the acid to make the salt
acid + base ???salt + water
2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2(aq) + 2 H2O(l)
the net ionic equation for an Acid-Base reaction is
H+1(aq) + OH-1(aq) ? H2O(l)
as long as the salt that forms is soluble in water
45. 45 Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Write the formulas of the reactants
HNO3(aq) + Ca(OH)2(aq) ?
Determine the ions present when each reactant dissociates
(H+ + NO3-) + (Ca+2 + OH-) ?
Exchange the ions, H+1 combines with OH-1 to make H2O(l)
(H+ + NO3-) + (Ca+2 + OH-) ? (Ca+2 + NO3-) + H2O(l)
46. 46 Write the formulas of the products
cross charges and reduce
HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2 + H2O(l)
Balance the Equation
may be quickly balanced by matching the numbers of H and OH to make H2O
coefficient of the salt is always 1
2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2 + 2 H2O(l) Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide
47. 47 Determine the solubility of the salt
Ca(NO3)2 is soluble
Write an (s) after the insoluble products and a (aq) after the soluble products
2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2(aq) + 2 H2O(l)
Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide
48. 48 Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Dissociate all aqueous materials to get complete ionic equation
not H2O
2 H+(aq) + 2 NO3-(aq) + Ca+2(aq) + 2 OH-(aq) ? Ca+2(aq) + 2 NO3-(aq) + H2O(l)
Eliminate spectator ions to get net-ionic equation
2 H+1(aq) + 2 OH-1(aq) ? 2 H2O(l)
H+1(aq) + OH-1(aq) ? H2O(l)
49. 49 Gas Evolving Reactions Some reactions form a gas directly from the ion exchange
K2S(aq) + H2SO4(aq) ? K2SO4(aq) + H2S(g)
Other reactions form a gas by the decomposition of one of the ion exchange products into a gas and water
K2SO3(aq) + H2SO4(aq) ? K2SO4(aq) + H2SO3(aq)
H2SO3 ? H2O(l) + SO2(g)
50. 50 Compounds that UndergoGas Evolving Reactions
51. 51 Process for Predicting the Products ofa Gas Evolving Reaction Determine what ions each aqueous reactant has
Exchange Ions
(+) ion from one reactant with (-) ion from other
Balance Charges of combined ions to get formula of each product
Check to see if either product is H2S
Check to see if either product decomposes, if so rewrite as H2O(l) and a gas
see table
Balance the Equation
Determine Solubility of Other Product in Water
52. 52 Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves Write the formulas of the reactants
Na2SO3(aq) + HNO3(aq) ?
Determine the ions present when each reactant dissociates
(Na+1 + SO3-2) + (H+1 + NO3-1) ?
Exchange the Ions
(Na+1 + SO3-2) + (H+1 + NO3-1) ? (Na+1 + NO3-1) + (H+1 + SO3-2)
53. 53 Write the formulas of the products
cross charges and reduce
Na2SO3(aq) + HNO3(aq) ? NaNO3 + H2SO3
Check to see either product H2S - No
Check to see of either product decomposes – Yes
H2SO3 decomposes into SO2(g) + H2O(l)
Na2SO3(aq) + HNO3(aq) ? NaNO3 + SO2(g) + H2O(l) Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves
54. 54 Balance the Equation
Na2SO3(aq) + 2 HNO3(aq) ? 2 NaNO3 + SO2(g) + H2O(l)
Determine the solubility of other product
NaNO3 is soluble
Write an (s) after the insoluble products and a (aq) after the soluble products
Na2SO3(aq) + 2 HNO3(aq) ? 2 NaNO3(aq) + SO2(g) + H2O(l) Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves
55. 55 Other Patterns in Reactions the precipitation, acid-base, and gas evolving reactions all involved exchanging the ions in the solution
other kinds of reactions involve transferring electrons from one atom to another – these are called oxidation-reduction reactions
also known as redox reactions
unlike the others, many of these reactions are not done by dissolving the reactants in water
56. 56 Oxidation-Reduction Reactions We say that the element that loses electrons in the reaction is oxidized
and the substance that gains electrons in the reaction is reduced
you cannot have one without the other
57. 57 Reactions of Metals with Nonmetals(Oxidation-Reduction) metals react with nonmetals to form ionic compounds
ionic compounds are solids at room temperature
the metal loses electrons and becomes a cation
the metal undergoes oxidation
the nonmetal gains electrons and becomes an anion
the nonmetal undergoes reduction
In the reaction, electrons are transferred from the metal to the nonmetal
2 Na(s) + Cl2(g) ? NaCl(s)
58. 58 Oxidation-Reduction Reactions any reaction that has an element that is uncombined on one side and combined on the other is a redox reaction
uncombined = free element
2 CO + O2 ? 2 CO2
2 N2O5 ? 4 NO2 + O2
3 C + Fe2O3 ? 3 CO + 2 Fe
Mg + Cl2 ? MgCl2
any reaction where a cation changes charge is redox
CuCl + FeCl3 ? FeCl2 + CuCl2
SnCl2 + F2 ? SnCl2F2
59. 59 Combustion Reactions Reactions in which O2(g) is a reactant are called Combustion Reactions
Combustion reactions release lots of energy
Combustion reactions are a subclass of Oxidation-Reduction reactions
60. 60 Combustion Products to predict the products of a combustion reaction, combine each element in the other reactant with oxygen
61. 61 Classifying Reactions one way is based on the process that happens
precipitation, neutralization, formation of a gas, or transfer of electrons
62. 62 Classifying Reactions another scheme classifies reactions by what the atoms do
63. 63 Synthesis Reactions also known as Composition or Combination reactions
two (or more) reactants combine together to make one product
simpler substances combining together
2 CO + O2 ® 2 CO2
2 Mg + O2 ® 2 MgO
HgI2 + 2 KI ® K2HgI4
64. 64 Decomposition Reactions a large molecule is broken apart into smaller molecules or its elements
caused by addition of energy into the molecule
have only one reactant, make 2 or more products
65. 65 Decomposition of Water
66. 66 Displacement Reactions also known as single-displacement reactions
Reactions that involve one anion being transferred from one cation to another
X ÅYq + A ® X + AÅYq
Zn(s) + 2 HCl(aq) ? ZnCl2(aq) + H2(g)
Fe2O3(s) + Al(s) ? Fe(s) + Al2O3(s)
2 Na(s) + 2 H2O(aq) ? 2 NaOH(aq) + H2(g)
67. 67 Displacement of Copper by Zinc
68. 68 Double Displacement Reactions two ionic compounds exchange ions
may be followed by decomposition of one of the products to make a gas
X ÅYq (aq) + A ÅBq (aq) ® XB + AY
precipitation, acid-base and gas-evolving reactions are also double displacement reactions