april 22, 2013 agenda: 1 – bellringer & part’n log 2 – cn: hess’s law & reaction...
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April 22, 2013
AGENDA:1 – Bellringer & Part’n
Log2 – CN: Hess’s Law &
Reaction Coordinate Diagrams
3 – Practice Problems4 – Work time
Today’s Goal:Students will be able to
use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams.
Homework1. Hess’s Law HW2. Week 31 make-up
QUIZ must be done by Friday.
3. Week 31 work is due by Friday.
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
5 minutes!
4 MINUTES REMAINING…
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
4 minutes!
3 MINUTES REMAINING…
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
3 minutes!
2 MINUTES REMAINING…
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
2 minutes!
1 MINUTE REMAINING…
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
1 minute!!!
30 seconds Remaining…
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
30 seconds!!!
10 Seconds Remaining…
BELL-RINGER TIME IS
UP!
April 22, 2013
AGENDA:1 – Bellringer & Part’n
Log2 – CN: Hess’s Law &
Reaction Coordinate Diagrams
3 – Practice Problems4 – Work time
Today’s Goal:Students will be able to
use Hess’s Law to calculate changes in enthalpy on reaction coordinate diagrams.
Homework1. Hess’s Law HW2. Week 31 make-up
QUIZ must be done by Friday.
3. Week 31 work is due by Friday.
Monday, April 22
Objective: Students will be able to use Hess’s Law to
calculate changes in enthalpy on reaction coordinate diagrams.
Bell Ringer:Describe each of the following situations
as either exothermic or endothermic reactions:
1. Temperature of the surroundings decreases.
2. Temperature of the surroundings increases.
REVIEW
Notes
Topic: Hess’s Law &Reaction Coordinate
DiagramsDate: 4/22/2013
Hess’s Law
Germain Hess (1802-1850) was a Swiss-born
Russian chemist and physician.
∆H = HProducts – Hreactants
∆H = HP – HR ∆H represents the
Change in Enthalpy over the course of the reaction.
If ∆H is… …POSITIVE The
reaction is ENDOthermic.
…NEGATIVE The reaction is EXOthermic.
Reaction Coordinate Diagrams
Exothermic
Time
En
thalp
hy (
J)
R
P
∆H = -
Endothermic
Time
En
thalp
hy (
J)R
P
∆H = +
Time
En
thalp
y
Time
En
thalp
yExamples
Hess’s Law:∆H = HP – HR
∆H = 600 J – 100 J∆H = + 500 J
endothermic
∆H = HP – HR
∆H = 200 kJ – 1000 kJ∆H = - 800 kJ
exothermic
HR=100J
HP=600J
HP=200kJ
HR=1000kJ
0
200
400
600
800
Time (s)
En
thalp
y (
J)
Cornell Notes (continued)
A chemical reaction had reactants with 200J of energy. To get the reaction started, 600J of energy were added. Then 700J of energy are released to form the products.
Trace the
steps of how to draw a
reaction coordina
te diagram.
R
P
Activation Energy (600J) = energy needed to make the reaction
happen spontaneously
∆H = HP – HR ∆H = 100J – 200J
∆H = -100J exothermic
∆H0
200
400
600
800
Time (s)
En
thalp
y (
J)
0
200
400
600
800
Time (s)
En
thalp
y (
J)
0
200
400
600
800
Time (s)
En
thalp
y (
J)
0
200
400
600
800
Time (s)
En
thalp
y (
J)
Example: Graph to Description
The reactants had J of
energy. An activation
energy of J was
required. The products
then had J of energy.
Overall, the reaction was
__thermic.
0
200
400
600
800
Time (s)
En
thalp
y (
J)
R
P300
400
500
endo∆H = HP – HR
∆H = 500J – 300J∆H = + 200J
endothermic
0
100
200
300
400
Time (s)
En
thalp
y (
J)Example: Graph to Description
The reactants had J of
energy. An activation
energy of J was
required. The products
then had J of energy.
Overall, the reaction was
__thermic.
R
P
350
50
100
exo∆H = HP – HR
∆H = 100J – 350J∆H = - 250J
exothermic
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