Specific heat capacity

From Free net encyclopedia

Template:Material properties (thermodynamics) The specific heat capacity (the symbol c or s, also called specific heat or SHC) of a substance is defined as heat capacity per unit mass. The SI unit for specific heat capacity is the joule per kilogram kelvin, J·kg^-1·K^-1, which is the amount of energy required to raise the temperature of one kilogram of the substance by one kelvin. Heat capacity can be measured by using calorimetry.

The equivalent definition using cgs units is the amount of energy (measured in ergs) required to raise the temperature of one gram of the substance by one degree Celsius (erg/(g·°C)). Other units of specific heat capacity include calories per gram degree Celsius (cal/(g·°C) or cal/(g·K)) and Btu per pound degree Fahrenheit (Btu/(lb·°F)).

The symbols c_p and c_v are often used to denote specific heat capacity at constant pressure and at constant volume.

Substances with low specific heat such as metals require less input energy to increase their temperature. Substances with high specific heat such as water require much more energy to increase their temperature. The specific heat can also be interpreted as a measure of how well a substance preserves its temperature, i.e. "stores" heat, hence the term "heat capacity".

1 Factors that influence heat capacity measurements
2 Table of specific heat capacities
3 Specific heat of building materials
4 See also

[edit]

Factors that influence heat capacity measurements

Temperature: Measuring the heat capacity of water produces different results if the starting point is 20 °C rather than 60 °C. Therefore the temperature at which the measurement was conducted must be specified for the value to be useful.
Intermolecular forces: Strong intermolecular forces combined with a disordered state (such as hydrogen bonding in liquid water) are likely to increase the heat capacity of a substance. In solid substances, heavy atoms tend to increase heat capacity by making quantum vibration modes more accessible by decreasing their spacing. In the case of an ideal gas, intermolecular forces are absent from the system, thus the specific heat capacity is independent of pressure which forces molecules closer together and to interact more often. Helium behaves much like an ideal gas at standard ambient temperature and pressure
For a gas, it is necessary to distinguish between specific heat at constant pressure (usually noted <math>c_p</math>) and at constant volume (usually noted <math>c_v</math>). The former, which is also the most commonly used, applies to a gas evolving at constant pressure (such as a gas being heated in a loose bag which allows free expansion), and the latter applies to a gas evolving at constant volume, such as a gas heated in a sealed container which does not change size. Contant pressure heat capacities are always the larger for a gas, because heat is absorbed to do the work which is done when the gas expands against external pressure, if it is allowed to do so. *Two analogous distinct capacities can also be defined for liquids and solids. The difference between the two is generally not worth considering at normally encountered conditions since liquids and solids are nearly incompressible at these pressures, so that their thermodynamic behavior is not significantly affected. On the other hand, at very high pressures (such as deep in the Earth) pressures can be high enough to not only change volumes of solids and liquids significantly, but also do a great deal of work with a relatively small change in volume. Here the difference between the two kinds of heat capacities again becomes important.

[edit]

Table of specific heat capacities

Substance	Phase	Specific heat capacity J·g^-1·K^-1
Air (dry)	gas	1.005
Air (100% humidity)	gas	≈ 1.030
Aluminium	solid	0.900
Beryllium	solid	1.824
Brass	solid	0.377
Copper	solid	0.385
Diamond	solid	0.502
Ethanol	liquid	2.460
Gold	solid	0.129
Graphite	solid	0.720
Helium	gas	5.190
Hydrogen	gas	14.300
Iron	solid	0.444
Lithium	solid	3.582
Mercury	liquid	0.139
Nitrogen	gas	1.042
Oil	liquid	≈ 2.000
Oxygen	gas	0.920
Silica (fused)	solid	0.703
Water	gas	2.020
	liquid	4.183
	solid (0 °C)	2.060
Standard ambient temperature and pressure used unless otherwise noted. For gases, the value given corresponds to <math>c_p</math>

[edit]

Specific heat of building materials

Usually of interest to builders and solar designers

Substance	Phase	Specific heat capacity J·g^-1·K^-1
Asphalt	solid	0.92
Brick	solid	0.84
Concrete	solid	0.88
Glass, crown	solid	0.67
Glass, flint	solid	0.503
Glass, pyrex	solid	0.753
Granite	solid	0.790
Gypsum	solid	1.09
Marble, mica	solid	0.880
Sand	solid	0.835
Soil	solid	0.80
Wood	solid	1.7

[edit]

Specific heat capacity

From Free net encyclopedia

Contents

Factors that influence heat capacity measurements

Table of specific heat capacities

Specific heat of building materials

See also

Views

Personal tools

Search

Partner sites