# Thermodynamics

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27 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

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Thermodynamics

Unit 10

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2

Thermodynamics

Thermo = heat

Dynamics = motion

Thermo + dynamics

=
Heat
(
Energy) Transformations

Review:

What is the difference between
heat

and
temperature
?

Heat (q):

Temperature:

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3

A FORM of energy

Flows from Hot

Cold

Measured in Joules

Measurement of
KE

Motion of
the particles

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4

Thermodynamics

You can measure heat energy (q) by
measuring the change in temperature:

m = Mass of substance in grams

c = Specific heat

D
T = Change in T = T
f

T
i

q = mc
D
T

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5

Thermodynamics

Specific Heat (c):

Energy needed to raise the temperature of 1
gram of a substance by 1
o
C.

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Thermodynamics

For Water:

c = =
4.184 J

g
o
C

This means it takes 4.184 Joules
of heat to raise 1 gram of
water 1
o
C.

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Thermodynamics

Examples:

How many joules would you need to raise the
temperature of 10.0 g of water from 12.3
o
C to
25.8
o
C?

q = ?

m = 10.0 g

c = 4.184 J/g
o
C

T
i

= 12.3
o
C

T
f

= 25.8
o
C

D
T = 25.8
-
12.3 = 13.5
o
C

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Thermodynamics

q = mc
D
T

q = (10.0g)(4.184 J/g
o
C)(25.8
o
C

12.3
o
C)

q = (10.0)(4.184)(13.5)

q =564.8

= 565 J

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9

Thermodynamics

-
425 Joules are released by an unknown amount
of water while cooling from 78.5
o
C to 45.6
o
C.
How many grams of water are present?

q =
-
425 J

m = ?

c = 4.184 J/g
o
C

T
i

= 78.5
o
C

T
f

= 45.6
o
C

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10

Thermodynamics

q = mc
D
T

-
425 J = m(4.184 J/g
o
C)(45.6
o
C

78.5
o
C)

-
425 = m(4.184)(
-
32.9)

-
425

=
m(
-
137.6)

-
137.6
-
137.6

m = 3.0888 g

= 3.09 g

Thermodynamics

Law of Conservation of Energy

Energy (Heat) cannot be created or
destroyed!

Remember heat flows from
hot

objects to
cold

objects.

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11

-
q
lost
= q
gained

Thermodynamics

Endo

chemical absorbs or takes in
energy or heat

** +q

Exo

chemical produces or gives off
energy or heat

**
-
q