April 17, 2012

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April 17, 2012

AGENDA:

1


Bell Ringer & Part. Log

2


Review HW

3


CN: Thermodynamics &
Hess’s Law

4


Work Time:
Thermodynamics & Hess’s
Law

Today’s Goal:

Students will be able to calculate
enthalpy using Hess’s Law.


Homework

1.
Thermodynamics & Hess’s
Law

2.
Extra Credit Work from
WEEK 30 is due Friday

Cornell Notes


Topic:

Thermodynamics & Hess’s Law


Date:

4/17/2012


Measuring energy:

Universe =
Surroundings

+
System


Surroundings



Surroundings

System

Heat





Heat


Endothermic


Exothermic

Review
from
yesterday

Cornell Notes

Heat Curve

= shows how temperature of the
surroundings

are changing during a chemical
reaction.



Diagram
Heat
Curves.

Temperature

Time

Exothermic

Temperature

Time

Endothermic

Temp. of
surroundings
will
increase
.

Temp. of
surroundings
will
decrease
.

Cornell Notes


Enthalpy “energy” (H)

= a measure of the
amount of heat “energy” in a
system

at
constant pressure


Hess’s Law:


H =
H
products



H
reactants

(Joules, J)

(


= “change in”)








Describe
enthalpy
& Hess’s
Law.

Enthalpy (J)

Time

Endothermic

Enthalpy (J)

Time

Exothermic

Cornell Notes


Reaction Coordinate Diagram

= shows
changes in enthalpy (heat) of a
system
.


Describe
Reaction
Coordinate
Diagrams.

Reactants have
more heat than
products

Products have
more heat than
reactants.

R

R

P

P


H =
+


H =
-

Cornell Notes

Summarize
what you
have
learned
today.


Thermodynamics



= study of
heat

movement



Energy (system) is
inverse

to temperature
(surroundings).


Enthalpy

Time

Enthalpy

Time

Examples

Hess’s Law:


H = H
P



H
R



H = 600 J


100 J


H = + 500 J





endothermic



H = H
P



H
R



H = 200 kJ


1000 kJ


H =
-

800 kJ





exothermic


H
R
=100J

H
P
=600J

H
P
=200kJ

H
R
=1000kJ