Specific Heat
The specific heat of a
substance is the quantity
of heat required to change
the temperature of 1 g of
o
that substance by 1 C.
The units of
specific heat in
joules are:
Joules


 gram oCelcius 


 J 
 g oC 


The units of
specific heat in
calories are:
 calories 
 gram oCelcius 


 J 
 g oC 


The relation of mass, specific heat,
temperature change (Δt), and quantity of
heat lost or gained is expressed by the
general equation:
(
)(
specific heat
of substance
)
mass of
Δt = heat
substance
Example 1
Calculate the specific heat of a solid in
J/goC and in cal/ goC if 1638 J raise the
temperature of 125 g of the solid from
25.0oC to 52.6oC.
(mass of substance)(specific heat of substance)Δt = heat
(g)(specific heat of substance)Δt = heat
heat = 1638 J
 heat 
specific heat = 

 g x Δt 
mass = 125 g
Δt = 52.6oC – 25.0oC = 27.6oC
1638 J

 0.475 J
=
specific heat = 
o
o 
g
C
 125 g x 27.6 C 
Calculate the specific heat of a solid in
J/goC and in cal/ goC if 1638 J raise the
temperature of 125 g of the solid from
25.0oC to 52.6oC.
Convert joules to calories using 1.000 cal/4.184 J
 0.475 J   1.000 cal  0.114 cal
specific heat =  o

 = g oC

 g C   4.184 J 
Example 2
A sample of a metal with a mass of 212
g is heated to 125.0oC and then dropped
into 375 g of water at 240.0oC. If the
final temperature of the water is
34.2oC, what is the specific heat of the
metal?
When the metal enters the water, it begins to cool,
losing heat to the water. At the same time, the
temperature of the water rises. This process continues
until the temperature of the metal and the temperature of
the water are equal, at which point (34.2oC) no net flow
of heat occurs.
A sample of a metal with a mass of 212
g is heated to 125.0oC and then dropped
into 375 g of water at 240.0oC. If the
final temperature of the water is
34.2oC, what is the specific heat of the
metal?
 Calculate the heat gained by the water.
 Calculate the final temperature of the metal.
 Calculate the specific heat of the metal.
A sample of a metal with a mass of 212
g is heated to 125.0oC and then dropped
into 375 g of water at 240.0oC. If the
final temperature of the water is
34.2oC, what is the specific heat of the
metal?
Heat Gained by the Water
temperature rise
of the water
Δt = 34.2oC – 24.0oC = 10.2oC
 4.184 J 
heat
heatgained
lost
o
4
(10.2
C)
=
= (375g ) o
1.60
x
10
J

by the metal
water
 gC 
A sample of a metal with a mass of 212
g is heated to 125.0oC and then dropped
into 375 g of water at 240.0oC. If the
final temperature of the water is
34.2oC, what is the specific heat of the
metal?
Once the metal is dropped into the water, its temperature
will drop until it reaches the same temperature as the
water (34.2oC).
temperature drop
of the metal
Δt = 125.0oC – 34.2oC = 90.8oC
A sample of a metal with a mass of 212 g is
heated to 125.0oC and then dropped into 375
g of water at 240.0oC.
If the final
temperature of the water is 34.2oC, what is
the specific heat of the metal?
The heat lost or gained by the system is given by:
(mass) (specific heat) (Δt) = energy change
heat 

rearrange specific heat = 

 mass x Δt 
specific heat
=
of the metal
 1.60 x 10 J   0.831 J 
 (212g)(90.8oC)    g oC) 


 
4
Energy in
Chemical Changes
In
all
chemical
changes,
matter
either
absorbs
or
releases energy.
Energy Release From
Chemical Sources
Type of Energy
Energy Source
Electrical
Storage batteries
Light
A lightstick. Fuel combustion.
Heat and Light
Combustion of fuels.
Body
Chemical changes occurring within body cells.
Chemical Changes Caused by
Absorption of Energy
Type of Energy
Chemical Change
Electrical
Electroplating of metals. Decomposition of water into
hydrogen and oxygen
Light
Photosynthesis in green plants.
Conservation of
Energy
An energy transformation occurs
whenever a chemical change occurs.

If energy is absorbed during a chemical
change, the products will have more
chemical potential energy than the
reactants.
•
If energy is given off in a chemical
change, the products will have less
chemical potential energy than the
reactants.
H2 + O2 have higher
potential energy than H2O
higher
energy
potential
is absorbed
energy
Electrolysis of Water
4.4
lower
energy
potential
is given
energy
off
Burning of
Hydrogen in Air
Law of
Conservation of
Energy
Energy can be neither created nor destroyed,
though it can be transformed from one form of
energy to another form of energy.