Temperature and Thermal Energy -

All solids, liquids, and gases are made up of molecules, which are constantly moving. Since molecules are always moving, they have kinetic energy. Kinetic energy is the energy of motion. One way to measure kinetic energy is in terms of temperature. Basically, temperature is the degree of hotness or coldness of a substance, as measured on a scale. Temperature scales usually indicate units of degrees Fahrenheit or degrees centigrade, or Celsius. At the molecular level, temperature is a measure of the average molecular kinetic energy of a substance. Stated another way, temperature is an indication of the average molecular motion in a substance. Another way to look at temperature is in terms of intensity. The faster the molecules of a substance move, the more intense their motion. The greater the intensity, the higher the temperature. Although the molecules in a substance are always moving, some molecules may move faster than others. Boiling water illustrates this principle. When water boils, some of the water molecules move fast enough to overcome the molecular forces holding them together and escape as steam. In general, boiling can be defined as the condition at which the molecules of a heated liquid become active enough to escape the liquid. In the case of water, the temperature has to reach 212 degrees Fahrenheit. Heat is a form of energy called thermal energy. In a sense, heat is the amount of thermal energy, and temperature is the intensity of the thermal energy. Two beakers of water can be used to illustrate the relationship between temperature and thermal energy. One beaker has only half as much water as the other. The temperature in the beaker with less water is 110 degrees Fahrenheit. The temperature in the beaker with more water is 100 degrees Fahrenheit. The beaker with more water contains more thermal energy and, therefore, more heat than the other beaker. Because there is more water, it takes more heat to raise the temperature of the water a given amount than it does to raise the temperature in the beaker with less water. Although the beaker with less water has less thermal energy, its energy is more intense than the energy in the beaker with more water. The average molecular motion in the beaker with less water is faster, so its temperature is higher. The two units generally used to measure heat are the British Thermal Unit, or BTU, and the calorie. A BTU is the amount of energy needed to raise the temperature of one pound of water one degree Fahrenheit. A calorie is the amount of energy needed to raise the temperature of one gram of water one degree Celsius.