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3/20/18
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Vocabulary1. Potential energy in the reactant2. Potential energy in the product3. Heat of reaction4. Catalyst5. Activation energy6. Activated complex7. Reactants 8. Products
Homework # 10.2Potential Energy Diagrams WS Aim: How can we represent the relationship
between the potential energy of the reactants and product of a chemical reaction?
H2O2
Pb(NO3)2 + KI PbI2 + KNO3
How do you prepare a chicken soup?
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Reactants Product
Chicken Soup
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Heat of reaction is the amount of heat given off or absorbed in a chemical reaction.
Reactants Products2H2 + O2 à 2 H2O + 571.6 KJ
∆H = HProducts - HReactants
∆H = PEP - PER
Open your reference table I, look at the first reaction and what information can you get from
there?
Type of chemical reaction: Combustion
What is an exothermic reaction?
• Exothermic reaction: release heat
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Table I How do you write a thermochemical equation?
CH4(g) +2O2(g) à CO2(g) + 2 H2O (l) + 890 KJ
Exothermic reaction
ΔH is written as a product
How do you write the thermochemical equation?
H2(g) + I2 (g) + 53.0 KJ à 2 HI(g)
ΔH is written as a reactant
53.0 KJ + H2(g) + I2 (g) à 2 HI(g)
Potential and Kinetic Energy Changes during a Collision
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KE is Converted to PE
KE PE
KE PE 2. Potential Energy Diagrams
Energy released or absorbed by a chemical reaction can be represented by a potential energy diagram.
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/activa2.swf
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3. Exothermic Reactions: See table I
CH4(g) + 2O2(g) à CO2(g) + 2H2O(l) + 890.4 KJ
Products: • decrease in potential energy.• increase in kinetic energy• released heat• ∆ H = negative
Where do compounds store energy?
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants Activated Complex Products
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Reactants
Activated Complex
ProductsPE
1. Is this an endothermic or an exothermic reaction?
2. What observable evidence indicates that a chemical reaction is taking place?
14KMnO4 + 4C3H5(OH)3 à 7K2CO3 + 7Mn2O3 + 5CO2 + 16H2O
H2OKNO3(s) + 34.89 KJ K+(aq) + NO3
-‐ (aq)
Products: • increase in potential energy.• decrease in kinetic energy: cold• absorbed heat• ∆ H = positive
Ammonium thiocyanate is mixed with barium hydroxide.
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A drop of water is placed on a block of wood. The bottom of the beaker becomes cold enough to freeze the water and stick to the wood.
1. Is this an endothermic or an exothermic reaction? Support your answer.
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Potential and Kinetic Energy Changes during a Collision
Reactants
Activated Complex
Products
Many cold packs used for treating sprains and aches are really just a bag of ammonium nitrate and water. When an athlete or sportsperson hurts themselves they mix the contents of the bag together and put it on the painful part of their body. The endothermic reaction takes heat out of their body …... this 'freezes' the painful area.
The smallest amount of energy needed to start a reaction: spark, flame, bunsen burner, and high temperature. Eac
Eac
Forward Reaction Reverse Reaction
A B
Eac = activation energy
PE
F.R.
R.R.
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PEPPER • Exothermic
H = PEP -‐ PER = PEP<PERA<B
• EndothermicH = PEP -‐ PER= PEP>PER A>B
6. Activated Complex
• The activated complex is the short-‐lived and unstable intermediate species located at the highest of the activation energy.
Reactants
Activated Complex
Products
7. Catalyst
• Speed up the reaction and lowers the activation energy.
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Eac
Catalyzed Reaction
Eac
Eac : ACTIVATION ENERGY
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• Ba(OH2) . 8 H2O (s) + 2 NH4SCN (s) = Ba(SCN) (aq) + 2 NH3 (aq) + 10 H2O
• When the solids become liquid, set the flask on a moist piece of wood. Hold until the water freezes and flask sticks to wood. Lift the flask to show its hold on the wood.
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