Post on 26-Mar-2015
transcript
BALANCING EQUATIONS &
CHEMICAL REACTIONS
Evidence of Chemical Change
Changes in Energy (E) Release of E as heat Release of E as light Production of sound Reduction or increase of
temperature Absorption or release of
electrical Energy
Formation of new substances
Formation of a gas Formation of a
precipitate Change in color Change in odor
Conservation of Mass
Law of Conservation of Mass In any physical or chemical reaction, mass
is neither created nor destroyed; it is conserved!
Reactants Products
Same number of atoms on both
sides of the equation!
Balancing Equations
In every balanced equationeach side of the equation
has the same number of atoms of each element
Important stuff!
Four abbreviations are used to indicate physical states of chemicals: shown as subscripts in the chemical equation
(s) = solid(l) = liquid(g) = gas(aq)= aqueous solution
(dissolved in water)
Symbols over the arrow indicate the conditions of the reaction
HeatPressureTemperatureCatalystReversible reaction
Balance this equation…
NaNO3 + CrCl3 NaCl + Cr(NO3)3
How would you “write” it?
Combination Reactionor Synthesis Reaction
Two or more simple substances react to form a more complicated one
A + B AB
Fe + S FeS
Combination Reactions
We can predict the products of ionic compounds by thinking about the charge!
Al (s) + O2 (g)
Cu (s) + S(s)
Are there 2 possible products to this reactionsHow would we “say” these equations?
Decomposition Reaction
A decomposition reaction is the opposite of a composition reaction - a complex molecule breaks down to make simpler ones.
AB A + B
2 H2O 2 H2 + O2
Decomposition Reactions
Harder to predict the products…always remember your diatomics.
Water is often a product!
HgO(s)
NH4NO3
Decomposition Reactions
HgO(s) 2HgO(s) 2Hg(l) + O2 (g)
NH4NO3 NH4NO3 N2O + 2H2O
The only way to really know is to do the reaction!!
Single Replacement
This is when one element trades places with another element in a compound.
A + BC AC + B
Mg + 2H2O Mg(OH)2 + H2
Single Replacement Reactions
Easy to predict the products. Look at the ions… remember that a cation has to bond to an anion!!
Don’t forget about diatomics!
Zn(s) + H2SO4(aq)
Na(s) + H2O
OOPS! Did we balance them?
Single Replacement Reactions
Zn(s) + H2SO4(aq) Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)
Na(s) + H2O Na(s) + H+OH-
(l) 2Na(s)+ 2H+OH-
(l) 2NaOH + H2(g)
Single Replacement Reactions
Reactivity of a metal makes a difference!
If a metal is more reactive than the metal it is displacing a rxn will occur. If the metal is less reactive than the metal it is displacing, a rxn will not occur.
Metal Reactivity
Increases down a group
Decreases across a period
Brainiacs-- Metal Reactivity
Reactivity in Single Displacement
Cs + KMnO4 CsMnO4
Will this occur??
Na + KMnO4 NaMnO4 + KWill this occur?
Double Replacement Reaction
This is when the anions and cations of two different molecules switch places, forming two entirely different compounds
AB + CD AD + CB
Pb(NO3)2 + 2KI PbI2 + 2KNO3
Double Replacement Reactions
Generally take place between two ionic compounds in aqueous solution
Pb(NO3)2 + 2KI PbI2 + 2KNO3
Double Replacement Reactions
2NaCl + H2SO4
Double Replacement Reactions
Ca(OH)2(aq) + 2HCl(aq) )
Combustion Reactions
A combustion reaction is when oxygen combines with another compound or element producing energy.
When hydrocarbons (C?H?) combust, water, carbon dioxide and energy are produced.
C10H8 + 12 O2 10 CO2 + 4 H2O + Energy
Combustion of Naphthalene
Combustion Reactions
Combustion of propane:
C3H8 + O2
Combustion of methane:
CH4 + O2
Combustion of butene (this one is tricky!)
C4H6 + O2
Teacher Demo Extraordinaire!
What is a flame video- Science Friday
http://www.sciencefriday.com/video/06/08/2012/what-is-a-flame.html
Recap: 5 Types of Reactions
1. Combination
2. Decomposition
3. Single Replacement
4. Double Replacement
5. Combustion
Warm Up: Predict the products, balance and classify the following reactions.
Li + MgCl2
C6H12 + O2
Ca(NO3)2 + NaOH
Types of Rxns Lab
Take about 10 minutes to do the prelab questions on the lab. Most of the answers should be in your CB notes.
Warm Up-
Balance the following combustion equations:
C4H4 + O2 CO2 + H2O
C3H6 + O2 CO2 + H2O
C7H14 + O2 CO2 + H2O
Types of Reaction Lab
a. Synthesis: Mg + O2
b. Decomposition CuCO3
c. Single Replacement Zn + HCl
d. Double Replacement PbNO3 + KI
Finish the lab
You have 20 minutes to get it done!
Be sure that all your questions are answered!
Debrief Types of Rxns Lab
Types of Reaction Lab
Synthesis: Mg + O2
Did the mass of the system change after the reaction took place?
Did you detect the presence of ammonia gas?
Endothermic or exothermic?
Types of Reaction Lab
Decomposition CaCO3
What evidence indicates a chemical reaction.
How do you know that carbon dioxide was formed?
Endothermic or exothermic?
Types of Reaction Lab
Single Replacement
Zn + HCl
What evidence did you see?
What was in the little tube– how do you know?
Endothermic or exothermic?
Types of Reaction Lab
Double Replacement
PbNO3 + KI
What evidence did you see?
Endothermic or exothermic?
Work on classifying the types of reactions on your balancing WS.
When you finish, you can start working on the back side of the Current Mole WS…. The front side should be complete!
Warm Up
Balance and classify the following reactions:
1.Zn + H2SO4 → H2 + Zn(SO4)2
2.CaCl2 + NaNO3 → Ca(NO3)2 + NaCl
3.C3H8 + O2 → CO2 + H2O
You should have most of these WS done!
1.Balancing equations WS– classified rxn type
2. Mole Practice WS…
Finish both of these… turn them in!
Work on the Review!
Due the beginning of class on Monday!
Test after we go over the review!!
Warm Up
Balance and classify the following reactions:
1.Na + H2CO3 → H2 + Na2CO3
2. NaF + Ca(NO3)2 → NaNO3 + CaF2
3. C5H12 + O2 → CO2 + H2O
Warm Up- part 2
Determine the molar mass of MgF2
Convert 5.7 g of magnesium fluoride to moles.
Convert 6.3 g of magnesium fluoride to molecules.
Warm Up Quiz
1. Determine the molar mass of Na3PO4
2. How many moles in 10.6g of Na3PO4
3. How many atoms in 0.50 mol Al?
4. How many atoms in 3.6 g of carbon?
Warm Up
Balance and classify the following reactions:
1.K + H3PO4 → H2 + K3PO4
3. CH12 + O2 → CO2 + H2O