� Specific heat- the amount of heat required to raise the temperature of one gram of a given
substance by one degree Celsius
� Because different substances have different compositions, each substance has its own
specific heat
Calculating Heat Evolved and Absorbed
� The temperature of water increases and decreases because of the specific heat of water,
but there are other factors that are important.
� Ex: An architect builds a house that is to be run by solar energy.
� The heat from the sun is stored in a solar pond which is made of 14,500 kg. of granite rock
and 22,500 kg. of water.
� The granite and the rock absorb the sun�s energy during daylight hours, but they lose
energy during the nighttime when there is no heat.
� The specific heat of water and granite indicate how much heat one gram of each substance
absorbs or releases when the temperature changes by 1degreesC.
� At the same temperature, 100 grams of water or granite absorb or release 100 times as
much heat as one gram. For the same 100 grams, increasing the temperature by 20
degrees Celsius requires so times as much heat as increasing the temperature one degree.
� The heat absorbed or released by a substance depends on specific heat, the mass of the
substance, and the amount by which the temperature changes.
� This relationship is expressed q = c x m x change in T
q = the heat absorbed or released
c = the specific heat of the substance
m = the mass of the sample in grams
change in T = the change in temperature in o Celsius
� change in T is the difference between the final temperature and the initial temperature or,
T final � T initial.
Example: (Solar Pond)
- the mass of the water is 22,500 kg which is equal to 2.25 x 10 to the 7 g
- the mass of the granite is 14,500 kg which is equal to 1.45 x 10to the 7 g
- For one day, the change in temperature is 22 degrees C
- The specific heat of water is 4.184 J/(g x degrees C) and the specific heat of granite is
0.803 J/(g x degrees C)
- Do the specific heats of each substance separately
- Use the formula shown above
For Water:
q = 4.184 J/(g x degrees C) x (2.25 x 107 g) x (22 degrees C) = 2.1 x 109 J
For Granite:
q = 0.803 J/(g x degrees C) x (1.45 x 107 g) x (22 degrees C) = 2.6 x 108 J
- You find the total amount of heat absorbed or released by adding the two quantities
qtotal = qwater + qgranite
qtotal = (2.1 x 109 J) + (2.6 x 108 J) = 2.4 x 109 J
- The solar pond will absorb 2.4 million kJ of heat during the day and release 2.4 million kJ
during the night
Using the Sun�s Energy
� The Sun is an inexhaustible source of energy, but it only shines for a fraction of the day
� Because of the variability of the sun, effective storage is critical
� Solar ponds take up a lot of space and can lose heat into the atmosphere
� Another method of storage is using hydrates which undergo and endothermic process with
the solution dissolves in the water of hydration
� At night, the hydrate re-crystallizes with the release of the absorbed solar energy
� Photovoltaic cells are a more promising approach to harnessing the sun�s energy in which
electronic devices convert solar radiation directly to electricity
� Although photovoltaic cells are the most efficient, they are costly and therefore not
commonly used
� The specific heat of a substance is a measure of how efficiently the substance absorbs heat
