Post on 25-Dec-2015
Chemical reactions are responsible for just about everything that occurs around us all the time.
How do you know a chemical reaction has taken place when a cake is baked?
What are some other examples of chemical reactions in real life?
MACROSCOPIC CHANES INDICATE A MICROSCOPIC CHANGE
OR CHEMICAL REACTION HAS TAKEN PLACE.
INDICATIONS OF A CHEMICAL REACTION
1. Gas is released (bubbles)
2. Light is released or absorbed
3. Odor is formed
4. Color change
5. Heat is released or absorbed
6. Precipitate is formed (solid from mixed liquids)
• During a chemical reaction energy is either released or absorbed.
• Endothermic reaction: energy is absorbed
• Exothermic reaction: energy is released (explosions)
- seen as heat and or light
CHEMICAL REACTION (same as chemical change)change of one substance into another substance
• original substance can not be recovered
• proper amounts of starting materials are needed, and all must be used to make finished product
• all amounts going in = amounts coming out
ex: building a bicycle
BICYCLE MATERIALSFrame, bolts, screws, nuts, wheels, handlebars,
seat, gears, etc…..
Would the bicycle work properly if there were nuts and bolts left over when it was built?
In chemical reactions the LAW OF CONSERVATION OF MASS
holds true
C + O2 CO2
Same numbers of atoms must beon each side of reaction
MASS IS CONSERVED
activity
CHEMICAL EQUATION• method of using chemical symbols to represent a
chemical reaction on paper
• describes what goes on in a chemical reaction
• easier than writing out words
Ex: 2 mols. of + one mol. of becomes 2 mols. of
hydrogen oxygen water
2 H2 + O2 2 H2O
PARTS OF A CHEMICAL EQUATION reactants “goes to” product
2 H (g) + O (g) ----------------- 2 H2O “becomes”
coefficient physical state subscript
Reactant- chemicals that will react , left side of the arrow
Product- chemicals that are produced, right side of arrow
Physical state- solid, liquid, gas
Arrow- shows direction of reaction and what reactants become
Coefficient- large numbers in front of chemical formulas represent number of atoms of each element in
molecule
Subscript- small number at lower right of chemical symbols represent number of atoms of that element in
molecule
COUNTING ATOMSRules1. Multiply subscript x coefficient
2. If parenthesis is present multiplysubscript of each x subscript x coefficienteach element outside
inside parenthesis parenthesis
3. Add total atoms
COUNTING ATOMS2 H2O H 2 x 2 = 4
O 1 x 2 = 2total 6
3 H2SO4 H 2 x 3 = 6S 1 x 3 = 3O 4 x 3 = 12 total 21
5 C6H12O6 C 6 x 5 = 30
H 12 x 5 = 60O 6 x 5 = 30total 120
Mg(OH)2 Mg 1 x 1 = 1O 1 x 2 x 1 = 2H 1 x 2 x 1 = 2total 5
3 Na(PO4)3 Na 1 x 3 = 3
P 1 x 3 x 3 = 9
O 4 x 3 x 3 = 36
total 48
BALANCING EQUATIONS
When a chemical reaction occurs between reactants there must always be equal number of atoms of
reactants and products.
WHAT LAW DOES THIS DEMONSTRATE?
REACTANT S PRODUCTS
NUMBER = NUMBER
OF ATOMS OF ATOMS
BALANCING EQUATIONS Rules1. Write all the reactants on the left side of arrow,
products on right side of arrow
2. NEVER change subscripts (this will change the reactant substance), ONLY change coefficients
Ex: H2O water H2O2 hydrogen peroxide
3. Find numbers of atoms of each elementEx: 2 H2O O = 2
H = 4
BALANCING EQUATIONSRules, cont.
4. Make sure to add up all sources of same element on each side of arrow
ex: 2 H2O + C2H4O6 do same with products
C 2 = C 2
H 4 + 4 = H 8
O 2 + 6 = O 8
5. Balance equation so that numbers of elements are equal on each side of the arrow (conservation of mass)
6. Simplify (reduce) equation to lowest terms (find common denominator)
ex: 4 NH3 + 2 O2 4 NO3 + 6 H2O (all divisible by 2, so simplify)
2 NH3 + O2 2 NO3 + 3 H2O
STEPS FOR BALANCING EQUATIONS
H2 + O2 H2O 1. List out the atoms on each side of
equation H H O O
2. Count number of each type of atom in reactants
H 2 O 2
3. Count number of each type of atom in products
H 2
O 1
4. Note which atoms are not balanced
H2 + O2 H2O
H 2 H 2
O 2 O 1 5. Select one atom to balance - easiest to start with atom which is by itself on one side - order: metal, nonmetal, save H & O last
H2O + O2 2 H2O
6. update atom counts on each side of equation
H 2 H 4 O 2 O 1
7. continue to update atom counts until both sides have equal numbers of atoms of each element
2H2O + O2 2 H2O BALANCED EQUATION!!!
8. Reduce coefficients if possible
4 NH3 + 12 O2 4 NO3 + 6 H2O
ALL COEFFICIENTS ARE DIVISIBLE BY 2 SO SIMPLIFY
2 NH3 + 6 O2 2 NO3 + 3 H2O
Al + Fe2O3 Al2O3 + Fe Al 1 Al 2 unbalanced Fe 2 Fe 1 unbalanced O 3 Fe 1
2 Al + Fe2O3 Al2O3 + Fe Al 2 Al 2 Fe 2 Fe 1 unbalanced O 3 O 3
2 Al + Fe2O3 Al2O3 + 2 Fe
ALL ATOMS EQUAL ON BOTH SIDESEQUATION IS BALANCED !
Mg Cl2 + K2S MgS + KCl Mg 1 Mg 1 Cl 2 Cl 1 unbalanced K 2 Cl 1 unbalanced S 1 S 1
Mg Cl2 + K2S MgS + 2 KCl
Mg 1 Mg 1 Cl 2 Cl 2 K 2 K 2 S 1 S 1
ATOMS ARE EQUAL ON BOTH SIDESEQUATION IS BALANCED !
P4O10 + H2O H2PO4 P 4 P 1 H 2 H 3 O 11 O 4
P4O10 + H2O 4 H2PO4
P 4 P 4 H 2 H 12 O 11 O 16
P4O10 + 6 H2O 4 H2PO4
P 4 P 4 H 12 H 12 O 16 O 16
PbO2 + HCl PbCl2 + Cl2 + H2O Pb 1 Pb 1 Cl 1 Cl 4 H 1 H 2 O 2 O 1
PbO2 + 4 HCl PbCl2 + Cl2 + H2O
Pb 1 Pb 1 Cl 4 Cl 4 H 4 H 2 O 2 O 1
PbO2 + 4 HCl PbCl2 + Cl2 + 2 H2O
Pb 1 Pb 1 Cl 4 Cl 4 H 4 H 4 O 2 O 2
Example of Parenthesis
(NH4)2 Cr2 O7 + Cr2O3 + N2 + H2O
N 2 N 2 Cr 2 Cr 2 H 8 H 2 O 7 O 4
(NH4)2 Cr2 O7 + Cr2O3 + N2 + 4 H2O
N 2 N 2 Cr 2 Cr 2 H 8 H 8 O 7 O 7
EQUATION IS BALANCED !
TYPES OF REACTIONS
Reactions are classified into types because it makes it easier to predict
what will happen during and at the results of that reaction.
Types of ReactionsSynthesis two or more substances or
combine to form a new single product- most exothermic
a + b ab 2H2 (g) + O2 (g) 2H2O
(g) element + element = new
cpd4 Fe (s) + 3 O (g) 2 FeO
(rust)
cpd + cpd = new cpd CO2 (g) + H2 (g) H2CO3
element + cpd = new cpdO2 (g) + CO (g) CO2 (g)
Types of ReactionsDecomposition:
compound breaks down into two or more simpler substances
ab a + b
2H2O (l) 2H2 (g) + O2
NH4NO3 (s) N2O (g) + 2 H2O
- most endothermic
Types of ReactionsSingle displacement:
- one element takes the place of another in a compound
- element can replace first or second part of a compound
- more reactive element will replace less reactive element
a + bc ac + b or
d + bc bd + c
Zn + Cu(NO3)2 Zn(NO3)2 + Cu
ele cpd new cpd new ele
Fe + CuSO4 FeSO4 + Cu
ele cpd new cpd ele
Cl2 + 2NaBr 2NaCl + Br2
Real Life Example of Single Displacement Reaction
Salicylic acid (C7H6O3) Aspirin
(C9H8O4)
Types of ReactionsDouble displacement
positive portions of 2 ionic compounds are interchanged
ab + cd ad + cbAgNo2 + NaCl AgCl +
NaNO3
cpd cpd cpd cpd
Pb(NO3)2 + 2 KCL PbI2 + 2 KNO2
Types of ReactionsCombustion:- Compound usually containing
carbon rapidly combines with oxygen to form one or more oxides (compound containing oxygen)
- called burning- heat is produced
ab + O2 oxide of a + oxide of b
CH4 + 2O2 CO2 + 2H2O
2C2H2 + 5O2 4CO2 + 2H2O + energy
Most reactions fall into these five categories, and some may fall into more than one .
NH4NO3 (s) N2O (g) + 2 H2O
Combustion- two new products contain oxygen (oxides)
Decomposition- one reactant is broken down into two simpler substances
NATURE OF REACTIONS
Reversible reaction• reaction that changes direction based on energy flow
Moves right: more product is madeMoves left: more reactants are formed
• shown with double arrow each way or one arrow pointing both directions
• reactants do not become used up because as new product is formed
other new products break down and supply new reactants
• reactions will try to reach a state of equilibrium equilibrium – state where no net change in amount of
reactants or products (a stable state)
Equilibrium Example
equilibrium does not mean there are equal numbers of products and reactants, amount of material started with = amount of material in end
Equilibrium Example
Rechargeable Batteries
Dynamic Equilibrium:state where 2 exactly opposite chemical reactions are occurring at the same place, same time, and same rate (speed) where reactions continuously occur
• Two opposing forces are being exerted but they are in a state of balance
• Amounts of all chemical entities are constant but do not have to be the same
ex: tug of war where both teams are pulling eqally against each other
Dynamic equilibrium example:• person rowing boat upstream at exactly same speed
as current - if current speeds up, he has to speed up - if current slows, he has to slow down to
stay in same place
• NET RESULT: boat has NO net movement even though person is still rowing and stream is still flowing
Equilibrium does not mean there are equal numbers of reactants and products
It means:
amount of material = amount of material
started with in end
CaCO3 CaO + CO2
Double arrow shows that reaction can go in either direction
Process of Dynamic Equilibrium1. at first reactions goes to right more quickly until more of
thereactants are used up
2. as more product is formed , the reverse reaction starts to
occur more frequently
3. eventually reaction moves at same speed in either direction
4. EQUILIBRIUM has been achieved
• DYNAMIC because molecules are always moving back and forth
• reactions try to stay at equilibrium because this is a stable state
What happens if you add stress to a reaction?
• If one side pulls harder there is more stress• Other side has to react and pull harder in order to
keep stability (equilibrium)
** same is true of chemical reactions **
Le Chateliers PrincipleIf a change of condition (stress) is applied to a chemical system, the reaction will return to equilibrium by shifting to counteract the stress
3 stresses1. change concentration of reactants or
products2. change temperature3. change pressure in system containing
gases
FACTORS THAT AFFECT DIRECTION OF REACTION
1. addition or removal of reactants or products
• addition of reactants/ removal of products: pushes reaction to right
• addition of products/ removal of reactants:
pushes reaction to left
FACTORS THAT AFFECT DIRECTION OF REACTION
2. addition or removal of energy
- addition: endothermic reactions absorb energy so more product made (reaction moves to right)
- removal: exothermic reactions give off energy to make more reactant (reaction moves to left)
In order for any reaction to occur energy is needed.
Activation energy: amount of energy needed to make atoms collide
ex: H and Oboth highly reactive elementscan coexist in the same container for years if just sitting
quietlyadd spark (energy) and they will cause an explosion
Hindenberg- spark ignited H with O and exploded
Space shuttle- liquid O is fine to go into space, but exploded when heat energy was added due to loss of heat shield shingles
Reaction rate: how fast a reaction occurs
Rate of reaction = amt substance changed/ amount of time
or amt of substance made in an
amt of time
Importance of Reaction Rate• Industry• Kitchen
• Body processes• Nature
FACTORS THAT AFFECT REACTION RATE
1. Temperature
2. Concentration of reactants
3. Catalysts
4. Inhibitors
FACTORS THAT AFFECT REACTION RATE
1. Temperature temperature rate
temperature rate
2. Concentrationconcentration rateconcentration rate
** Higher amounts of substance and temperature will increase numbers of collisions **
limiting reactant: reactant which is depleated first (not the one with the lesser amount)
• concentration of reactants is important because ifwe run out of one of the reactants it can limit and stop
the whole reaction
ex: How many smores can be made with the following?
6 graham crackers3 marshmallows2 pieces of chocolate
Which ingredient is the limiting reactant?
How many bicycles can be made if the following is needed?
1 bicycle = 1 frame + 2 wheels
We have:100 frames120Wheels
Which component is the limiting reactant?
How many bikes can be made?
FACTORS THAT AFFECT REACTION RATE
3. Catalysts: - substance that speeds up a reaction without
being itself changed or used up
- lowers activation energy needed to start reaction
- most powerful catalysts found in nature
ex: enzymes
4. Inhibitors:Substance that slows down a reaction, doesn’t completely stop reaction
Ex: stabalizers in products, retardents