Whether bound or free, water’s chemical formula remains the same, Water is a very small molecule consisting of three atoms – one oxygen atom flanked by two hydrogen atoms (H2O). Water may exist as a gas (steam or humidity), liquid or solid (ice). The distance between the molecules determines these differences, and the distances are influenced by temperature. At very low temperatures, ice forms as the water molecules line up very close together. Elevating the temperature increases the movement of the water molecules against each other, pushing them farther away from each other. When enough heat is applied, ice melts into a liquid. Continued heating transforms liquid water into a gas (steam) by giving the molecules freedom to move even farther apart. The variations of water from solid to liquid to gas are called changes in state, In spite of the obvious differences in these states, they do not involve any changes in the structure of the water molecule.
It takes heat, or its loss, to move the molecules of water through their different states, and this heat is commonly measured in the form of calories, expressed with a lowercase “c”. This unit of measurement is equal to the amount of energy required to raise 1 gram of water 1o Celsius. The energy value of foods are measured in thousands of calories, more accurately expressed as “kilocalories” and represented by the terms “kcal” or “calories” with an uppercase “C”. One kilocalories equals 1,000 calories. In theory, the small “c” calorie is used by chemists, while the large “C” Calorie or more commonly, kilocalories is the more accurate term of referring to the energy value of foods.
It takes more energy to heat water than any other substance presently known. Water’s high specific heat makes it unique compared to other compounds on earth. Given the same amount of heat, a metal pan or the oil in it will become burning hot, while water will become only lukewarm. This important characteristic of water enables animals, including people, with their high water content to withstand the very cold temperatures sometimes found on earth. Water’s specific heat of 1.00 ( 1 calorie will raise 1 gram of water 1oC) is used as the measure against which all other substances are compared. Similarly, water differs from other compounds in the amount of energy it takes to reach its specific freezing, melting and boiling points.