The temperature of 2.0 L of water
increases from 5.0° C to 25° C.
How much does its volume
increase?
ǻV = ViȕǻT
ǻT = 25°C í 5.0°C = 20 C°
ǻV = (2.0 L)(2.07×10í^4 1/C°)(20 C°)
ǻV = 0.0083 L
18.12 - Specific heat
Specific heat: A
proportionality constant that
relates the amount of heat
flow per kilogram to a
material’s change in
temperature.
Specific heat is a property of a material; it is a
proportionality constant that states a relationship between the heat flow per kilogram of
a material and its change in temperature.
A material’s specific heat is determined by how much heat is required to increase the
temperature of one kilogram of the material by one kelvin. A material with a greater
specific heat requires more heat per kilogram to increase its temperature a given
amount than one with a lesser specific heat. In spite of its name, specific heat is not an
amount of heat, but a constant relating heat, mass, and temperature change.
The specific heat of a material is often used in the equation shown in Equation 1. The
heat flow equals the product of a material’s specific heat c, the mass of an object
consisting of that material, and its change in temperature. The illustration in Equation 1
shows how specific heat relates heat flow to change in temperature. As you can see
from the graph, lead increases in temperature quite readily when heat flows into it,
because of its low specific heat.
In contrast, water, with a high specific heat, can absorb a lot of energy without changing
much in temperature. Temperatures in locations at the seaside, or having humid
atmospheres, tend to change very slowly because it takes a lot of heat flow into or out of the water to accomplish a small change in
temperature. Summer in the desert southwest of the United States is famous for its blazing hot days and chilly nights, while on the east coast
of the country the sweltering heat of the day persists long into the night. Materials with large specific heats are sometimes informally called
“heat sinks” because of their ability to store large amounts of internal energy without much temperature change.
Above, you see a table of some specific heats, measured in joules per kilogram·kelvin. The specific heat of a material varies as its temperature
and pressure change. The table lists specific heats for materials at 25°C to 30°C (except for ice) and 10^5 Pa pressure, about one atmosphere.
Specific heats vary somewhat with temperature, but you can use these values over a range of temperatures you might encounter in a physics
lab (or a kitchen).
Specific heat of a material
Relates heat and temperature change,
per kilogram