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Do Now - April 20+8, 2009
1. You have 2 minutes to list the 4 types of chemical reactions. After you are finished, write your objectives and wait for further instructions.
Do Now - April 20+8, 2009
1. List the 4 types of chemical reactions.2. List 2 characteristics of combustion
reactions.3. Using the following reaction, answer
the following questions:1) Is the equation balanced?2) Will this reaction actually
occur?3 Ni + 2 AuBr3 3 NiBr2 + Au
Agenda• Do Now/Announcements• Double-Replacement Reactions• What is energy?• Energy Diagrams: Endo/Exothermic• Foldable Work Time• Exit Ticket
Objectives
•SWBAT relate the law of conservation of energy to chemical reactions.
•SWBAT distinguish between endothermic and exothermic reactions using descriptions, chemical equations, and graphs.
Single Replacement
Example: Zn + CuCl2
ZnClCl Cu +
AB + C AC + B
ClCl Zn Cu+
•Such experiments reveal trends. The activity series ranks the relative reactivity of metals.•It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom.Q: Which of these will react?
1. Fe + CuSO4 2. Ni + NaCl 3. Li + ZnCO3 4. Al + CuCl2
Cu + Fe2(SO4)3Yes, Fe is above CuNR (no reaction)
No, Ni is below Na
Zn + Li2CO3Cu + AlCl3
Yes, Al is above Cu
KNaLiCaMgAlZnFeNiSnPbHCuHgAgAu
Yes, Li is above Zn
Reactivity of Halogens• The same goes for halogens• More active halogens will replace less
active halogens• List also on page 288• Q: Which of these will react?
5. F2 (g) + 2 NaBr (aq)
6. I2 (g) + 2 KCl (aq)
F
Cl
Br
I
Yes, F is above Br
2 NaF (aq) + Br2 (l)
NR (no reaction)
No, I is below Cl
Single-ReplacementPractice Problems
Predict the products of the following reactions.
Fe (s) + CuSO4 (aq)
Br2 (l) + MgCl2 (aq)
Mg (s) + AlCl3 (aq)
KNaLiCaMgAlZnFeNiSnPbHCuHgAgAu
4. Double Replacement
It’s like exchanging partners!• A reaction which involves an exchange of
ions between two compounds
compound + compound new compound + new compound
AX + BY AY + BX
KNOW THIS!
4. Double Replacement
AX + BY AY + BXA and B are cations (positively
charged)X and Y are anions (negatively
charged)You can see the anions have switched
places and are now bonded to the other cations in the reaction
Examples of Double Replacement Reactions
Ca(OH)2(aq) + 2 HCl(aq) CaCl2(aq) + 2 H2O(l)
Ions: Ca+2, OH-1, H+1, Cl-1
WATER IS FORMED!
2 NaOH(aq) + CuCl2(aq) 2 NaCl(aq) + Cu(OH)2(s)
Ions: Na+1, OH-1, Cu+2, Cl-1
SOLID IS FORMED - PRECIPITATE
KCN (aq) + HBr (aq) KBr (aq) + HCN (g)
Ions: K+1, CN-1, H+1, Br-1
GAS IS FORMED
Double Replacement
Example: MgO + CaS
AB + CD AD + CB
SOMg Ca
+O S
Mg Ca+
Double Replacement Practice Problems
• Page 291
Objectives
•SWBAT relate the law of conservation of energy to chemical reactions.
•SWBAT distinguish between exothermic and endothermic reactions using descriptions, chemical equations, and graphs.
Energy
•Energy is the ability to do work or produce heat
UNITS: kilojoules (kJ)
Two forms: 1) Potential
2) Kinetic(page 489)
Potential Energy
Potential energy is due to composition or position of an object
In chemistry, this has to do with types of atoms, number and types of bonds, and arrangements of atoms.
(page 489)
Kinetic Energy
• Kinetic energy is the energy of motion
• In chemistry, this describes the motion of particles (page 490)
Law of Conservation of Energy
• The Law of Conservation of Energy states that in any chemical reaction, energy can be converted from one form to another, but it cannot be created or destroyed (page 490)Energy Reactants = Energy
Products
Chemical Potential Energy
• Chemical potential energy is energy stored in a substance because of its composition (page 490)
• Example: C8H18 <-- Octane (gasoline)– Gasoline burns (combusts) and
produces heat
Energy in Chemical Reactions
• In every molecule, there is energy stored in the bonds– It takes energy to keep the atoms
together
•Since the molecules change during a chemical reaction, the amount of energy keeping them together changes
• More energy might be needed or extra energy might be let go
Endothermic Reactions
•When MORE energy is needed to keep the new molecules together energy is absorbed from somewhere else
•The energy goes INSIDE the molecules•Taking away energy to put it in molecules
makes the reaction area feel COLD•This is called an endothermic reaction
– Endo- means inside•THINK: Endo- and in
Endothermic Reactions
•Using the notes you just took, write a good definition for endothermic reaction
Exothermic Reactions•When LESS energy is needed than before
the extra energy is released •The extra energy goes OUTSIDE the
molecules•The energy is used to make the
molecules move faster, which makes the reaction area feel HOT
•This called an exothermic reaction– Exo- means outside
•THINK: Exo- and exit
Exothermic Reactions
•Using the notes you just took, write a good definition for exothermic reaction
Exit Ticket
• Write your own definitions for endothermic/exothermic reactions