iiiiiiivv s.panzarella chemical reactions & equations
TRANSCRIPT
I II III IV VS.Panzarella
Chemical Reactions & Equations
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Chemical Equations
A + B C + D
REACTANTS PRODUCTS
• Shows what takes place during a chemical reaction
•Reactant : (substances reacting) on left•Arrow - (→) at center ; yields or produces•Products: (new substances formed) on right
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Coefficients: how many? ; # appears in FRONT of the formula “molecules” for covalent substances
“moles“ of atoms “units” for ionic substances
3CO2
2Mg
4MgO
3 molecules of carbon dioxide
2 moles of magnesium
4 units of magnesium oxide
Phases: • solid (s), liquid (l), gas (g), aqueous (aq)
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Example:
Names of reactants: methane & oxygen Names of products: carbon dioxide & water
CH4 + 2O2 CO2 + 2H2O
How many of each (coefficient):
__CH4 ____O2 ____CO2 ___H2O
Ratio of coefficients: ___: ____: ___: ___
reactants products
1 2 1 2
11 2 2
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Expressing Chemical Equations
Word: carbon + oxygen yields carbon dioxide
Remember your diatomic gases: (BrINClHOF)
C + O2 → CO2
Formula
→+Diagram:
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Exothermic & Endothermic Processes – see RB pg 34 table 2.5
Exothermic: release energy; surrounding temp increases; NRG on the product side A + B → AB + energy
- CH4 + 3 O2 → CO2 + 2 H2O + energy
Endothermic: absorb energy; surrounding temp decreases; NRG on the reactant side
AB + energy→ A + B
- H2O(s) + energy → H2O (l)
Endothermic video http://www.youtube.com/watch?v=5RJLvQXce4A
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Law of Conservation of Mass/Matter/NRG
Matter is neither created nor destroyed in chemical reactions. In any chemical total numbers & kinds of atoms must remain unchanged in the reaction.
For chemical equations, this is called a balanced equation.
Charge, energy, mass, and # atoms are conserved (unchanged) in balanced reactions
4 H
2 O
4 H
2 O
4 g 32 g
36 g
How well did you focus? Partner How well did you focus? Partner Chat…Chat… Obtain a plastic baggie containing a substance. List 2 physical observations of the substance. Feel the outside of the baggie. Note the temperature.
Add some water to the baggie and seal mixing the two substances. List 2 physical observations of the substance. Feel the outside of the baggie. Note the temperature. When finished dispose of the baggie into the garbage.
SUMMARYSUMMARY:: All reactions involve heat (energy). The substance in the baggie is NH4Cl(s) .
When mixed with water, the solid dissolves forming NH4Cl(aq) . The reaction for this is as such:
NHNH44ClCl(s) (s) NH NH44+ +
(aq) (aq) + Cl+ Cl - -
(aq) (aq)
REFLECTIONREFLECTION: answer on a separate sheet of paper: answer on a separate sheet of paper1. Was the reaction endothermic or exothermic? Explain/give evidence to
support your answer.2. Would the term “heat” go on the reactant side or the product side of the
equation?3. According to Reference Table I, was your answer correct? What is the
amount of heat involved per 1 mole of substance produced? (Hint – look for this reaction)
4. In terms of entropy ( s), does it increase, decrease or RTS as the reaction proceeds from reactant to product? (Hint – look at phases)
5. Would this substance when placed in water conduct electricity? Support your answer.
When finished check your homework answers on the side overhead screen.
HH22OO
Chemical Change – chemical composition changes
Physical Change – chemical composition remains the same
Examples :Ripping, tearing, breakingBoiling, melting, freezing, vaporing a substance (a phase change)dissolving
Examples :Burning, rusting, oxidizingFlammable, explosive, reacting
Signs of a Chemical ReactionSigns of a Chemical ReactionEvolution of heat and light Evolution of heat and light Formation of a gasFormation of a gasFormation of a precipitate (solid)Formation of a precipitate (solid)Color changeColor change
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I II III IV VS.Panzarella
II. Balancing Equations
Chemical Reactions
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A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!
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B. Helpful Tips
Balance one element at a time. Update ALL atom counts after adding
a coefficient. If an element appears more than
once per side, balance it last. Balance polyatomic ions as single
units. “1 SO4” instead of “1 S” and “4 O”
Al + CuCl2 Cu + AlCl3
Al
Cu
Cl
1 1
1 1
2 3
2
3
6
3
33 2
C. Balancing Example
Aluminum and copper(II) chloride react to form copper and aluminum chloride.
2
2
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I II III IV VS.Panzarella
Chemical Reactions
III. Types of Chemical Reactions
Target: I can recognize the types of chemical reactions
TASK 1: Individual Read silently pages 37-40 in your review book. Complete the section on page 7 in your guide (PREFERABLY IN PENCIL) that is based on the reaction tag you have.
TASK 2 : Square OFF (teams of 4)nTaking turns, “teach” your type of reaction to the group so they can complete the reactions #1-4 on page 7. nGuide pg 8 - complete #1-20. Each person in the group should be prepared to explain and/or answer questions from the teacher upon completion.
TASK 3: Teacher Check for understanding & Reaction #5 : Combustion
TASK 4: Independent Homework: Review book pg 40 #59
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A. Combustion
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
the burning of any substance in O2 to produce heat
A + O2 B + H2O
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Na(s)+ O2(g)
C3H8(g)+ O2(g) 5 3 4
A. Combustion
Products: contain oxygen hydrocarbons form CO2 + H2O
CO2(g)+ H2O(g)
Na2O(s) 4 2
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B. Synthesis or Direct Combination
the combination of 2 or more substances to form a compound
only one product
A + B AB
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B. Synthesis
H2(g) + Cl2(g) 2 HCl(g)
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Al(s)+ Cl2(g) AlCl3(s)2 3 2
B. Synthesis
Products: ionic - cancel charges
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C. Decomposition
a compound breaks down into 2 or more simpler substances
only one reactant
AB A + B
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C. Decomposition
2 H2O(l) 2 H2(g) + O2(g)
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KBr(l) K(s) + Br2(l) 2 2
C. Decomposition
Products: binary - break into elements
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D. Single Replacement
one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-)
A + BC B + AC
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D. Single Replacement
Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)
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Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)
D. Single Replacement
Products: metal metal (+) nonmetal nonmetal (-) free element must be more active (check activity
series-Table J)
Br2(l)+ NaCl(aq) N.R.
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AB + CD AD + CB
E. Double Replacement
ions in two compounds “change partners” cation of one compound combines with
anion of the other
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E. Double Replacement
Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)
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Pb(NO3)2(aq)+ KI(aq) PbI2(s)+ KNO3(aq)
E. Double Replacement
Products: switch negative ions one product must be insoluble (check
solubility table)
NaNO3(aq)+ KI(aq) N.R.
2 2
I II III IV V
IV. Stoichiometry
• Study of QUANTITATIVE relationships between
substances to determine the PROPORTIONS in a chemical
relationship
The COEFFICIENTS of the FORMULAS in the balanced equation indicate the relative number of moles, molecules and volume (at STP) 0 OC & 1 atm
When working with chemical equations it is assumed that:
1. The reaction is a forward reaction (no side reactions).
2. The reaction goes to completion. 3. The reactants are completely used.
LIMITING REACTANT- LIMITS THE AMOUNT OF PRODUCT FORMED
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• Remember: Law of Conservation of Mass- • MASS and ENERGY are conserved in
EVERY chemical reaction (so is the charge)
1) Determining Mole Ratio (doesn’t give mass ratio)• Use the coefficient to get a mole
ratio:
2 C2H6 + 7 O2 4 CO2 + 6 H2O
• Mole ratio: • This means that 2 moles of C2H6
combine with 7 moles of O2 to produce 4 moles of CO2 and 6 moles of water.
2). Problem Solving using Stoichiometric calculations - start with the given (use factor label method or set up as a proportion)
I have 5 eggs. How many cookies can I make?
3/4 c. brown sugar1 tsp vanilla extract
2 eggs2 c. chocolate chips
Makes 5 dozen cookies.
2 1/4 c. flour1 tsp. baking soda
1 tsp. salt1 c. butter
3/4 c. sugar
5 eggs 5 doz.
2 eggs= 12.5 dozen cookies
Ratio of eggs to cookies
A) Mole-Mole and volume-volume Problems (gases only at STP)
REMEMBER moles and volume are directly related: 1 mol = 22.4 L
Example #1: mol-molHow many moles of water will be produced from the complete combustion of 3 moles of ethane (C2H6 )?
2 mol C2H6 3 mol C2H6
= 6 mol H2O
x mol H2O= 9 mol H2O
2 C2H6 + 7 O2 4 CO2 + 6 H2O? mol3 mol
EquationProblem
How many liters of ethane can be completely oxidized by a reaction with 63 liters of oxygen gas?
2 L C2H6 X L C2H6
= 7 L O2
63 L O2
= 18 L O2
2 C2H6 + 7 O2 4 CO2 + 6 H2O
? L 63 L
EquationProblem
Ex. #2 vol-vol
Ex #3: mol-molAssuming at STP, how many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen. (this is called the Haber Process)
1 mol N2
X mol N2
= 2 mol NH3
5.5 mol NH3
= 2.75 mol N2
N2 + 3 H2 2 NH3? mol .60 mol
Ex #4: vol –mol Using the above equation, how many liters of nitrogen are needed to produce 5.5 moles of NH3?
x 22.4 L = 61.6 L N2
1 mol N2
2 mol NH3 .60 mol NH3
= 1 mol N2 x mol N2
= .3 mol N2
Stoichiometry Steps1. Write a balanced equation.2. Identify known & unknown.3. Line up conversion factors.
Mole ratio - moles moles Molar mass - moles grams Molar volume - moles liters gas
Core step in all stoichiometry problems!!
• Mole ratio - moles moles
4. Check answer.
Conversion factors in stoich
Molar Mass(g/mol)
6.02 1023
particles/mol
MASSIN
GRAMSMOLES
NUMBEROF
PARTICLES
LITERSOF
SOLUTION
Molar Volume (22.4 L/mol)
LITERSOF GASAT STP
Molarity (mol/L)
Ex #1. How many grams of silver will be formed from 12.0 g of copper?
Cu + 2AgNO3 → 2Ag + Cu(NO3)2
12.0 g Cu x 1 mol Cu = .19 moles Cu 64 g/mol Cu
? g = ? mol
a. g-mol
B). Mass-Mass Problems (convert g→ mol→ mol→ g)
b. mol-mol ratio 1 mol Cu = 2 mol Ag = 10.5 mol Ag .19 mol Cu x mol Ag
c. mol-g 10.5 mol Ag x 108 g Ag = 1134 g Ag 1 mol Ag
Ex #2. What mass of silver nitrate is required to liberate 54 g of silver?
Cu + 2 AgNO3 → Cu(NO3) 2 + 2 Ag
54 g Ag x 1 mol Ag = .5 moles Ag 108 g/mol Ag
a. g-mol
B). Mass-Mass Problems (convert g→ mol→ mol→ g)
b. mol-mol ratio2 mol AgNO3 = 2 mol Ag = .5 mol AgNO3 X mol AgNO3 .5 mol Ag
c. mol-g.5 mol AgNO3 x 170 g AgNO3 = 85 g AgNO3
1 mol AgNO3
x g = ? mol
54 g = ? mol
3Wa4 + 12Ch + 16Ma 4Wa3Ch3Ma4
3 cups of water 12 tablespoons of chocolate 16 marshmallows Produce 4 servings of Hot Chocolate
Using the balanced equation and the factor label method determine the amount of water, chocolate and marshmallows needed to produce 1 serving.
Group Activity: Limiting Reactants
3Wa4 + 12Ch + 16Ma 4Wa3Ch3Ma4
1 serving x 1 serving x 3 c. water3 c. water = ¾ c water = ¾ c water
4 servings4 servings
1 serving x 1 serving x 12 T chocolate12 T chocolate = 3 T chocolate = 3 T chocolate
4 servings4 servings
1 serving x 1 serving x 16 marshmallows16 marshmallows = 4 marshmallows = 4 marshmallows
4 servings4 servings