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CHAPTER 6Chemical Reactions and Equations
Warm-up
Who can recall what the 4 pictures were on the intro slide for this chapter?
Fire
Test tube with a blue solid substanceTwo flasks (one with a blue liquid and one with a yellow liquid)
Smoke trail
What do all of these things have to do with chapter 6?
They all show signs of a chemical change
Indications of a Chemical Change
Chemical ChangeThe change of one or more substances into new substances by the rearrangement of atoms.
4𝐹𝑒(𝑠 )+3𝑂2 (𝑔)→2𝐹𝑒2𝑂3(𝑠 )
Change in energy
Formation of a Precipitate(two liquids combine and a solid is produced)
Formation of a gas
Change in color
Parts of a Chemical Equation
Reactants
Physical States(solid, liquid, gas or aqueous)
Coefficients
Products
4𝐹𝑒 3 (𝑠)𝑂2(𝑔)(𝑠) 2𝐹𝑒2𝑂3+¿ →
Writing Equations
Word EquationsUsing the names of chemicals to describe chemical reactions
𝑠𝑜𝑙𝑖𝑑𝑠𝑜𝑑𝑖𝑢𝑚+ h𝑐 𝑙𝑜𝑟𝑖𝑛𝑒𝑔𝑎𝑠→ 𝑠𝑜𝑙𝑖𝑑𝑠𝑜𝑑𝑖𝑢𝑚 h𝑐 𝑙𝑜𝑟𝑖𝑑𝑒
Chemical EquationsUsing chemical formulas and numbers to describe chemical reactions
𝑁𝑎( 𝑠)+𝐶𝑙2 (𝑔)→𝑁𝑎𝐶𝑙( 𝑠)Hopefully you noticed that this equation defies the Law of Conservation of Matter. It is not balanced. Once you master writing equations, you will also learn how to balance equations.
Practice ProblemsUse your ion tables
Solid copper + fluorine gas = solid copper (II) fluoride
Re-write the following chemical equation in words
Re-write the following word equation as a chemical equation
aqueous calcium chloride + Aqueous lithium chromate
aqueous lithium chloride
Solid calcium chromate +
Cu(s) + F2(g) CuF2 (s)
+ energy
2𝐻2𝑂(𝑙)+𝒆𝒏𝒆𝒓𝒈𝒚→2𝐻2 (𝑔)+𝑂2 (𝑔)
EnergyWhen chemical reactions take place, energy is either absorbed or released in the process
An endothermic reaction
An exothermic reaction
Warm up
Watch the following video to complete the warm up
http://www.youtube.com/watch?v=R6bBs2D0cpA
Write the following chemical equation for the reaction that occurred in the video:
Aluminum + iodine = aluminum iodide
You should be able to answer the following questions:
What are the reactants?What are the products?What was the indication that a chemical change took place?Was this an endotherm or exothermic reaction?
Physical States of ElementsMetalso Metals are always represented by their symbols from the
periodic table, with no subscripts
o All metals, with the exception of mercury are solid and will have an (s) following their symbols in an equation
Cu(s)
Non-metalso Are often diatomic (Br,I,N,Cl,H,O,F) so they will
have a subscript of 2.o Most of these diatomic elements will be a gas
except iodine (s) and bromine (l)
Cl2(g)
Physical States of Ionic CompoundsIonic Compoundso Their physical state will be
o (aq) = aqueous if they can dissolve in water (soluble)o (s) = solid if they can’t (insoluble)
Use this table to determine the solubility of ionic compounds:
More Practice ProblemsWhat would be the physical states of the following substances if written in a chemical equation?
PbI2 __________ KNO3 ____________
KI __________ Pb(NO3)2 ____________
Write the following equation with physical states:
Lead (II) nitrate combines with potassium iodide to form potassium nitrate and lead (II) iodide.
(s)
(aq)
(aq)
(aq)
Pb(NO3)2(aq) + KI(aq) KNO3(aq) + PbI2(s)
Warm-up
Watch the following video to see what happenshttp://www.youtube.com/watch?v=BhO8kGrc4dg
Write the chemical equation for the reaction:(Use a solubility table to predict the physical states of each compound)
potassium iodide + lead (II) nitrate = potassium nitrate and lead (II) iodide
Did you write the correct physical state for each compound in the reaction?
Balancing Chemical EquationsWhy?To demonstrate the Law of Conservation of Mass which states:
In a chemical reaction mass is neither created or destroyed
Antoine Lavoisier
What must be conserved?The number and type of atoms
2𝑁𝑎(𝑠 )+𝐶𝑙2 (𝑔)→2𝑁𝑎𝐶𝑙(𝑠 )
2 sodium atom + 2 chlorine atoms = 2 sodium atoms + 2 chlorine atoms
How to Balance a Chemical Equationo Make sure that both sides of an equation have an
equal number of each type of atom represented.
o Balance equations by adding coefficients.
o Never mess with subscripts
NaBrMgClMgBrNaCl ________ 22
Na
Cl
Mg
Br
Strategies for Balancing Chemical Equations1. The even/odd combination
Make the subscript of one, the coefficient of the other and vice versa.
Iron (III) oxide Iron + Oxygen
232 3402 OFeFe
322 ______ OAlOAl Practice:
Strategies Continued2. Balance groups as a whole if the elements of the group
are only represented in the group on each side of the equation.
MgOHAlAlOHMg __)(____)(__ 32
Mg
OH
Al
MgKClOKClOMg ______)(__ 424 Practice:
Strategies Continued3. Balancing Hydrocarbon Combustion Reactions
The first step is to add a coefficient to the hydrocarbon so that the total number of hydrogens in the molecule is divisible by four. Then, balance the product side of the equation before finishing up with oxygen.
0____0____ 2225 HCOCH C
H
O
Practice: 0____0____ 22262 HCOHC
Strategies Continued4. Splitting Water
When hydroxide shows up on one side of an equation and water is on the other side, split water into H(OH) to balance out hydroxide.
OHMgSOSOHOHMg 23322 ______)(__
Practice: OHAlBrHBrOHAl 233 ______)(__
Things to Keep in Mind• Again, do not mess with subscripts• In the final solution, the coefficients have to be in the
lowest whole number ratio.
• If at first you don’t succeed, try, try again! Most of the solutions to these problems come from trial and error.
OHOH 222 424 OHOH 222 22
Comprehensive Practice Problem Write the equation Note the physical state of each substance Balance the equation
Potassium chromate combines with lead (II) nitrate to form potassium nitrate and lead (II) chromate
Warm-up
If I put all the reactants of the following equation into the left side of the balance and all of the products into the right side, why would the balance look like this?
Types of Chemical Reactions
• 5 General Types• Synthesis• Decomposition• Single displacement• Double displacement• Combustion
You will need to know how to identify these reactions
Combustion
CxHy + O2 CO2 + H20
SynthesisA + B AB
(Two elements combine to form a compound)
DecompositionAB A + B
(One compound splits to form two compounds)
Types of Chemical Reactions – 5 General Formulas
Always the products of these combustion reactions
Reactions Cont.Single Replacement (Single Displacement)
A + BC AC + B (Metals replace metals and non-metals replace non-
metals)
Double Replacement (Double Displacement)
AB + XY AY + XB (Compounds switch partners)
Practice Problems
Identify the type of reaction
)(2)()(32
)(4)(42)(2
)()(2)(
)(2)(2)(2)(104
)(4)()(342)(
342
2
22
0108132
32)(3
)(
gss
aqaqaq
sgs
lggg
ssaqs
OFeOFe
LiClCaCrOCrOLiCaCl
MgOOMg
HCOOHC
BaSOFeSOFeBa
s
Combustion Decomposition Single replacememt
Synthesis Double Replacement
Warm-up
What type of reaction does the picture represent?
What are the reactants in this reaction?
Which one will run out first?
Equilibrium http://www.youtube.com/watch?v=JsoawKguU6A
• Many reactions can change direction.
• These are called reversible reactions.
• When no net change occurs in the amount of reactants and products, a system is said to be in equilibrium.
• A system in which opposite actions are taking place at the same rate, it is said to be in dynamic equilibrium.
• Products and reactants are forming at the same rate.
• Reactants are never fully used up because they are constantly being formed from products.
Reaction Rate http://www.bing.com/videos/search?q=activation+energy+video&mid=CC5874704F3D6F93469CCC5874704F3D6F93469C&view=detail&FORM=VIRE7
• How fast do reactions reach equilibrium?
• The amount of energy the particles must have when they collide is called the activation energy of that reaction.
• The speed of reaction measures how quickly the reactants disappear or how quickly the products appear.
• The amount of substance changed per unit time is the rate of reaction.
Factors that Affect the Rate of a Reaction
Temperature affects the rate of reaction also.The higher the temperature, the faster the reaction; the lower the
temperature, the slower the reaction.
The amount of substance present in a certain volume is called the concentration of the substance.
• Raising the concentration of a reactant will speed up a reaction because there are more particles per volume
• When one reactant is used up, the reaction will stop• The reactant that is used up first is called the limiting reactant
Factors that Affect the Rate of a Reaction
• Presence of a catalyst speeds up the rate of a reaction without being permanently changed of used up itself.
• A catalyst speeds up the reaction by lowering the activation energy.
• Biological catalysts are called enzymes.
• Reactions that have undesirable products sometimes have to be slowed down.
• A substance that slows down a reaction is called an inhibitor.