Types of Energy
1. Potential Energy
Energy an object has due to its position
2. Kinetic Energy
Energy an object has due to its motion
http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/
Potential Energy (PE) Types
• Gravitational Potential Energy
• Chemical Potential Energy
• Nuclear Potential Energy
http://chemsite.lsrhs.net/chemKinetics/PhaseChangeEnergy.html
http://chemistry.tutorvista.com/nuclear-chemistry/nuclear-reaction.html
http://www.concord.org/~ddamelin/chemsite/chemKinetics/reactionsAndPotential.html
Kinetic Energy (KE) Types
• Thermal Energy
• Light
• Sound
http://greenhabbing101.com/green-rehab-tip-of-the-week-a-thermal-energy-audit-for-your-greenrehab-project/
http://schools.look4.net.nz/science/biology/plant/photosynthesis
http://mrconsidinescience.blogspot.com/2013/11/energy-transforms.html
Chemistry Universe
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0m/s09-02-enthalpy.html
Endo- and Exo- thermic
or
Energy
http://staff.norman.k12.ok.us/~cyohn/index_files/ThermochemistryNotes_files/image043.jpg
or
Energy
Law of Conservation of Energy
Energy cannot be created nor destroyed, but
it can change form.
How does this apply to reactions?
In an exothermic reaction,
the energy goes from the
system (candle) to the
surroundings mainly as
thermal energy and light, but
energy is not destroyed.
http://www.buzzle.com/articles/exother
mic-reaction-examples.html
PhET
How does this simulation show the Law of
Conservation of Energy?
Energy Transformations
• Energy transformations happen when one
form of energy is changed to another.
EOC Question
Collision Theory
In order for a reaction to occur:
1. Atoms/ions/molecules must first collide.
2. They must have the proper orientation.
3. They must collide with enough energy.
Improper Orientation
Not Enough Energy
http://collegefootball.ap.org/content/mississippi-hopes-build-close-loss
Proper Orientation
Enough Energy
http://www.hardydiagnostics.com/newsletters/2012_December.html
Products
Collision
•Correct Orientation
•Sufficient Energy
No
Rxn
Collision
Rebound
•Incorrect Orientation
•Sufficient Energy
No
Rxn
Collision
•Correct Orientation
•Insufficient Energy
Rebound
Collision Summary Questions
1. What is an “effective collision”?
2. Do all collisions cause a reaction?
3. What can you do in the lab to
make more effective collisions
occur?
Potential Energy Diagrams
Show the PE changes that occur as reactants
become products during a chemical change
http://www.kentchemistry.com/links/Kinetics/PEDiagrams.htm
Endothermic v Exothermic Reactions
What is different between the two types?
Where are the reactants? Products?
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
Endothermic v Exothermic Reactions
What is the same between the two types?
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
PE Diagram Terms
Activation Energy (Ea): minimum amount of
energy input needed for a chemical
reaction to occur.
Activation Energy
Where would the activation energy be
shown in each of these? Why?
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
PE Diagram Terms
Activated Complex:
a temporary,
unstable
arrangement of
atoms after an
effective collision;
where old bonds are
broken and new
bonds are formed
http://www.chem.ox.ac.uk/vrchemistry/chapter15/html/page29.htm
Activated Complex
Where would the activated complex be
shown in each of these?
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
PE Diagram Terms
• Enthalpy Change (ΔH): Difference between
the PE of the products and reactants in a
chemical reaction.
• Energy can be absorbed or released.
Enthalpy Change (ΔH)
+∆H
-∆H
Where would change in enthalpy be shown?
Would ΔH be positive or negative?
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
Enthalpy Change (ΔH)
• An extensive property
• Cannot be measured directly
http://chemistry.about.com/od/photogalleries/ig/Fla
sks-and-Beakers/Flask-of-Pink-Liquid.htm
http://www.alphahatch.com/chicktec-6thermometer-498-p.asp
http://www.vernier.com/products/interfaces/labpro/
Making a PE Diagram
A Potential Energy Diagram can be made
from observed enthalpy changes for a
given reaction.
2H2 + O2 → 2H2O
→
ΔH = -572 kJ
Construct a PE diagram. Include particle
diagrams for reactants, products, and the
activated complex.
PE Diagram for Water Formation
=?
=-572 kJ
http://staff.prairiesouth.ca/~chemistry/chem30/2_kinetics/kinetics3_2.htm
Bonds
Is making new bonds to form products or
breaking old bonds in reactants endothermic?
Practice Question A
What is the energy of:
http://www.kentchemistry.com/links/Kinetics/PEDiagrams.htm
6.
7.
1.
2.
3.
4.
5.
Reactants?
Activated Complex?
Products?
Activation Energy?
Enthalpy Change?
Is this reaction endothermic or
exothermic?
How do you know your answer to #6?
Practice Question C
Identify the following reactions as endothermic
or exothermic, and calculate ΔH if possible.
1.
3.
2.
4.
Practice Question D
Use the information provided to sketch an
energy diagram for the reaction.
PEproducts = 20 kJ
PEreactants = 40 kJ
PEactivated complex = 100 kJ
http://www.kentchemistry.com/links/Kinetics/PEDiagrams.htm
Practice Question E
Use the information provided to sketch an
energy diagram for the reaction.
PEreactants = 40 kJ
PEproducts = 15 kJ
Ea = 10 kJ
http://www.kentchemistry.com/links/Kinetics/PEDiagrams.htm
Practice Question F
Use the information provided to sketch an
energy diagram for the reaction.
PEactivated complex = 400 cal
PEreactants = 100 cal
ΔH = 200 cal
(cal)
http://dmechem.wordpress.com/category/charts-and-diagrams/
Calculating ΔH
ΔH can be calculated based on PE diagrams
or on enthalpy values of products and
reactants.
Before calculating ΔH, the total enthalpy of
products and reactants must be
determined.
2H2 + O2 → 2H2O
0
(kJ)
-572
ΔH = ΔH(2 H2O) – ΔH(2 H2 + O2)
= (-572 kJ)– (0 kJ)
= -572 kJ
2H2 + O2 → 2H2O
Compound
H2 (g)
O2 (g)
H2O (l)
ΔHf°
(kJ/mol)
0
0
-286
To find enthalpy, apply coefficients
ΔH = ΔH(2 H2O) – ΔH(2 H2 + O2)
=(-286 kJ/mol)(2 mol) – {(0 kJ/mol)(2 mol)+(0 kJ/mol)(1 mol)}
= -572 kJ
EOC Question
Practice Question B
Identify the following reactions as
endothermic or exothermic.
1. ΔH = +100 kJ
endothermic
2. ΔH = -5 kJ
exothermic
3. The beaker holding a reaction
exothermic
became hot to the touch.
4. The temperature in the room
dropped by 0.7°C.
endothermic
5. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
ΔH = -215 kcal/mol
exothermic