If you'd like to learn more about the specific heat of water at the molecular level, check out this video on the specific heat of water from Khan Academy.
Looking at water, you might think that it's the most simple thing around. Pure water is practically colorless, odorless, and tasteless. But it's not at all simple and plain and it is vital for all life on Earth. Where there is water there is life, and where water is scarce, life has to struggle or just "throw in the towel. Water temperature plays an important role in almost all USGS water science. Water temperature exerts a major influence on biological activity and growth, has an effect on water chemistry, can influence water quantity measurements, and governs the kinds of organisms that live in water bodies.
The people in the photo above are all experiencing different temperatures depending which part of the beach they are on. Those in the water are most likely feeling cooler than those on the sand. This is due to the high specific heat capacity of water. In other words, the same amount of heat energy when applied to sand and water will increase the temperature of the sand. Skip to main content. Search Search. Water Science School.
Specific Heat Capacity and Water. This particular resource used the following sources:. Skip to main content. Search for:. Specific Heat and Heat Capacity. Calorimetry requires that the material being heated have known thermal properties, i. The classical rule, recognized by Clausius and by Kelvin, is that the pressure exerted by the calorimetric material is fully and rapidly determined solely by its temperature and volume; this rule is for changes that do not involve phase change, such as melting of ice.
There are many materials that do not comply with this rule, and for them, more complex equations are required than those below. These experiments mark the foundation of thermochemistry. Constant-volume calorimetry is calorimetry performed at a constant volume. This involves the use of a constant-volume calorimeter one type is called a Bomb calorimeter.
For constant-volume calorimetry:. To find the enthalpy change per mass or per mole of a substance A in a reaction between two substances A and B, the substances are added to a calorimeter and the initial and final temperatures before the reaction started and after it has finished are noted. Multiplying the temperature change by the mass and specific heat capacities of the substances gives a value for the energy given off or absorbed during the reaction:.
Dividing the energy change by how many grams or moles of A were present gives its enthalpy change of reaction. This method is used primarily in academic teaching as it describes the theory of calorimetry. It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself. In addition, the object placed inside the calorimeter shows that the objects transferred their heat to the calorimeter and into the liquid, and the heat absorbed by the calorimeter and the liquid is equal to the heat given off by the metals.
A constant-pressure calorimeter measures the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant. An example is a coffee-cup calorimeter, which is constructed from two nested Styrofoam cups and a lid with two holes, allowing insertion of a thermometer and a stirring rod.
The inner cup holds a known amount of a solute, usually water, that absorbs the heat from the reaction. When the reaction occurs, the outer cup provides insulation.
The measurement of heat using a simple calorimeter, like the coffee cup calorimeter, is an example of constant-pressure calorimetry, since the pressure atmospheric pressure remains constant during the process. Constant-pressure calorimetry is used in determining the changes in enthalpy occurring in solution. An ideal gas has different specific heat capacities under constant volume or constant pressure conditions. This represents the dimensionless heat capacity at constant volume; it is generally a function of temperature due to intermolecular forces.
Macroscopic measurements on heat capacity provide information on the microscopic structure of the molecules. Molecular internal vibrations : When a gas is heated, translational kientic energy of molecules in the gas will increase.
In addition, molecules in the gas may pick up many characteristic internal vibrations. Potential energy stored in these internal degrees of freedom contributes to specific heat of the gas.
Measuring the heat capacity at constant volume can be prohibitively difficult for liquids and solids. That is, small temperature changes typically require large pressures to maintain a liquid or solid at constant volume this implies the containing vessel must be nearly rigid or at least very strong.
It is easier to measure the heat capacity at constant pressure allowing the material to expand or contract freely and solve for the heat capacity at constant volume using mathematical relationships derived from the basic thermodynamic laws. The heat capacity ratio or adiabatic index is the ratio of the heat capacity at constant pressure to heat capacity at constant volume.
It is sometimes also known as the isentropic expansion factor:. For an ideal gas, evaluating the partial derivatives above according to the equation of state, where R is the gas constant for an ideal gas yields:. Julius Robert Mayer : Julius Robert von Mayer November 25, — March 20, , a German physician and physicist, was one of the founders of thermodynamics.
His achievements were overlooked and credit for the discovery of the mechanical equivalent of heat was attributed to James Joule in the following year. It is a simple equation relating the heat capacities under constant temperature and under constant pressure. Calorimeters are designed to minimize energy exchange between the system being studied and its surroundings. They range from simple coffee cup calorimeters used by introductory chemistry students to sophisticated bomb calorimeters used to determine the energy content of food.
Calorimetry is used to measure amounts of heat transferred to or from a substance. The heat supply under constant pressure simultaneously causes an increase in volume, for which a part of the energy is used up. The distinction is of importance only in the consideration of gases and vapors. The specific heat capacity of solids is used primarily in the construction industry for the assessment of the behavior of building material.
In summer, fabrics with high heat capacity keep the rooms cool for a long time. In winter, they keep the heat in the buildings longer.
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