calorie, abbr. cal, unit of heat energy in the metric system. The measurement of heat is called calorimetry. The calorie, or gram calorie, is the quantity of heat required to raise the temperature of 1 gram of pure water 1°C. The kilocalorie, or kilogram calorie, is the quantity of heat required to raise the temperature of 1 kg of pure water 1°C; it is equal to 1,000 cal. The kilocalorie is used in dietetics for stating the heat content of a food, i.e., the amount of heat energy that the food can yield as it passes through the body; in this context, the kilocalorie is usually called simply the calorie. The amount of heat energy needed to effect a 1°C temperature increase in 1 gram of water varies with temperature (see heat capacity); thus the temperature range over which the heating takes place must be stated to define the calorie precisely. The 15° calorie, or normal calorie, is widely used in chemistry and physics; it is measured by heating a 1-gram water sample from 14.5°C to 15.5°C at 1 atmosphere pressure. The 4° calorie, also called the small calorie or therm, is measured from 3.5°C to 4.5°C (water is most dense at 3.98°C); the large calorie, or Calorie, is equivalent to 1,000 small calories. The average value of the calorie in the range 0°C to 100°C is called the mean calorie; it is 1⁄100 of the energy needed to heat 1 gram of water from its melting point to its boiling point. The calorie may also be defined by expressing its value in some other energy units. The 15° calorie is equivalent to 4.185 joules (J), 1.162×10−6 kilowatt-hours, 3.968×10−3 British thermal units, and 3.087 foot-pounds; the 4° calorie equals 4.204 J; and the mean calorie equals 4.190 J. Two other calories sometimes used are the International Steam Table calorie, equal to 4.187 J, and the thermochemical calorie, equal to 4.184 J. When the calorie is used for precision measurement of heat energy, the particular calorie being used must be specified. The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved. See more Encyclopedia articles on: Physics
Heat
Heat Heat is a way of transferring energy between a system and its surroundings that often, but not always, changes the temperature of the system. Heat is not conserved, it can be either created or destroyed. In the metric system, heat is measured in units of calories, which are defined as the amount of heat required to raise the temperature of one gram of water from 14.5oC to 15.5oC. In the SI system, the unit of heat is the joule.
Heat Capacity The heat capacity of a substance is the amount of heat required to raise the temperature of a defined amount of pure substances by one degree (Celsius or Kelvin). The calorie was defined so that the heat capacity of water was equal to one. 
Specific Heat The specific heat of a substance is the number of calories needed to raise the temperature of one gram by 1oC. Because one degree on the Celsius scale is equal to one Kelvin, specific heats in the metric system can be reported in units of either cal/g-oC or cal/g-K. The units of specific heat in the SI system are J/g-K. Because there are 4.184 joules in a calorie, the specific heat of water is 4.184 J/g-K. The ease with which a substance gains or loses heat can also be described in terms of its molar heat capacity, which is the heat required to raise the temperature of one mole of the substance by either 1oC or 1 K. In the metric system, the units of molar heat capacities are therefore either cal/mol-oC or cal/mol-K. In the SI system the units of molar heat capacities are J/mol-K.
Latent Heat When ice is heated, the heat that initially enters the system is used to melt the ice. As the ice melts the temperature remains constant at 0oC. The amount of heat required to melt the icehas historically been called the latent heat of fusion. Once the ice has melted, the temperature of the water slowly increases from 0oC to 100oC. But once the water starts to boil, the heat that enters the sample is used to convert the liquid into a gas and the temperature of the sample remains constant until the liquid evaporates. The amount of heat required to boil, or vaporize, the liquid has historically been called the latent heat of vaporization.
More than 200 years ago, Joseph Black distinguished between sensible heat and latent heat. Heat that raises the temperature of the system can be sensed, but heat that results in a change in the state of the system from solid to liquid or from liquid to gas is latent. Like the latent image on photograph film that hasn't been developed or latent fingerprints that can't be seen with the naked eye, latent heat is heat that enters the system without changing the temperature of the system.
Heat and The Kinetic Molecular Theory The system is the small portion of the universe in which we are interested, such as the water in a beaker or a gas trapped in a piston and cylinder, as shown in the figures below. The surroundings are everything elsein other words, the rest of the universe.
The system and its surroundings are separated by a boundary. Heat is transferred across the boundary between a system and its surroundings. One of the fundamental principles of the kinetic theory is the assumption that the average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else. A gas becomes warmer if and only if the average kinetic energy of the gas particles increases. Heat, when it raises the temperature of a system, produces an increase in the speed with which the particles of the system move, as shown in the figure below.
First...What is the difference between HEAT and TEMPERATURE?
Specific Heat Capacity (C or S ) - The quantity of heat required to raise the temperature of a substance by one degree Celsius is called the specific heat capacity of the substance. The quantity of heat is frequently measured in units of Joules(J). Another property, the specific heat, is the heat capacity of the substance per gram of the substance. The specific heat of water is 4.18 J/g° C.
q = m x C x DT q = m x C x (Tf - Ti) q = amount of heat energy gained or lost by substance m = mass of sample C = heat capacity (J oC-1 g-1 or J K-1 g-1) Specific Heat Instructional Videos
More High School Examples Highlight Answer Box to reveal answers
Even More Practice Questions
|
The amount of heat required to raise the temperature of 1g of something by 1 c, is called what?
Postagens relacionadas
direito autoral © 2024 mesadeestudo Inc.
