Specific heat measures the amount of thermal energy needed to raise the temperature of a substance by a certain amount. It is expressed in joules and is important in science, engineering, and climate. Heat energy and temperature are different concepts. Specific heat and heat capacity are often confused, but the former is independent of the amount of substance, while the latter is dependent on it. Water has a high specific heat, which is essential for stabilizing the Earth’s climate.
Specific heat is a measure used in thermodynamics and calorimetry that indicates the amount of thermal energy required to raise the temperature of a given mass of a particular substance by a certain amount. Although several different scales of measurement are sometimes used, this term usually refers specifically to the amount required to raise 1 gram of a substance by 1.8°F (1° Celsius). It follows that if twice as much energy is added to a substance, its temperature should increase twice as much. Specific heat is usually expressed in joules, the unit typically used in chemistry and physics to describe energy. It is an important factor in science, engineering and understanding the earth’s climate.
Heat and temperature
Heat energy and temperature are two different concepts and understanding the difference is important. The first is a quantity in thermodynamics that describes the amount of change a system can cause to its environment. The transfer of this energy to an object causes its molecules to move more rapidly; this increase in kinetic energy is what is measured, or experienced, as an increase in temperature.
Specific heat and heat capacity
These two properties are often confused. The first is the number of joules required to raise the temperature of a given mass of a substance by a few units. It is always given “per unit of mass”, for example 0.45 j/g°C, which is the specific heat of iron, or the number of joules of heat energy required to raise the temperature of one gram of iron by one degree Celsius. This value is therefore independent of the amount of iron.
Heat capacity – sometimes called “thermal mass” – is the number of joules required to raise the temperature of a particular mass of material by 1.8°F (1°Celsius), and is simply the specific heat of the material multiplied by its mass. It is measured in joules per °C. The heat capacity of an iron object weighing 100 g would be 0.45 X 100, with a value of 45 j/°C. This property can be thought of as the ability of an object to store heat.
The specific heat of a substance is more or less true over a wide range of temperatures, i.e. the energy required to produce a one degree increase in a given substance varies only slightly with its initial value. It does not apply, however, when the substance undergoes a change of state. For example, if heat is continuously applied to a quantity of water, there will be an increase in temperature based on the specific heat of the water. Once the boiling point is reached, however, there will no longer be any increase; instead, the energy will go into producing water vapor. The same is true for solids when their melting point is reached.
An outdated measure of energy, the calorie, is based on the specific heat of water. A calorie is the amount of energy required to raise the temperature of one gram of water by 1.8°F (1°C) at normal air pressure. It is equivalent to 4,184 joules. Slightly different values can be given for the specific heat of water, as it varies slightly with temperature and pressure.
effects
Different substances can have very different specific heats. Metals, for example, tend to have very low values. This means they heat up quickly and cool down quickly; they also tend to expand significantly as they get hotter. This has implications for engineering and design: expansion of metal parts in structures and machinery often has to be accounted for.
Water, on the other hand, has a very high specific heat: nine times that of iron and 32 times that of gold. Due to the molecular structure of water, a large amount of energy is required to raise its temperature by even a small amount. It also means that hot water takes a long time to cool down.
This property is essential for life on Earth, as water has a significant stabilizing effect on global climate. During the winter, the oceans cool slowly and release a significant amount of heat into the environment, which helps keep global temperatures reasonably stable. Conversely, in the summer, a large amount of heat is needed to significantly raise ocean temperatures. This has a moderating effect on the climate. Continental interiors, away from the ocean, experience much greater temperature extremes than coastal regions.
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