Calorie, unit of energy

Table 1.3 gives some commonly used non-SI units for certain quantities, together with conversion factors relating them to SI units. We use these in some examples and problems, except for the calorie unit of energy. This last, however, is frequently encountered. 

Calcination slow heating of a substance without causing it to melt Calorie unit of energy equivalent to the energy required to raise the temperature of one gram of water from 14.5°C to 15.5°C, equivalent to 4.18 J... 

The SI Systeme International d Unites) unit of energy is the joule (J) An older unit is the calorie (cal) Most or game chemists still express energy changes in units of kilocalories per mole (1 kcal/mol = 4 184 kJ/mol)... 

The basic unit of energy used in accelerator physics is the electron volt (eV), which is the energy acquired by an electron when accelerated through a potential difference of one volt. An electron volt is a very small unit compared to an energy unit such as a food calorie (kilocalorie). A kilocalorie is about 26 billion trillion times as large as an eV. Common multiples of eV arc McV (niillion cV), GcV (billion cV), and TcV (trillion eV). 

The joule, symbol J, is the unit of energy in the science connntinity. It is not widely used outside the science community in the United States, but it is elsewhere. For example, in the United States, the energy content of a food product is likely expressed in food calories. This energy could be expressed in joules, and that is being done in many parts of the world. A Diet Coca Cola in Australia is labeled Low Joule rather than Low Cal as in the United States. To obtain a feeling for the size of a joule, consider the following statistics ... 

Measurements of energy are made in terms of absolute joules, but engineering practice has persistently retained the thermochemical calorie as the unit of energy. The two are related by the definition ... 

The most common units of energy that we use in the study of thermodynamics are the joule and the calorie. The joule (J) is ... 

Some Sl-derived units with special names are included in Table 2.2. The standard atmosphere may be used temporarily with SI units it is dehned to be equal to 1.01325 X 10 Pa. The thermochemical calorie is no longer recommended as a unit of energy, but it is defined in terms of an SI unit, joules, symbol J, as 4.184 J [4]. The unit of volume, liter, symbol L, is now defined as Idm. ... 

A unit of energy (symbolized by J) equal to 10 ergs. In the SI system, the joule replaces the calorie, which is equivalent to 4.184 J. Formally, the joule equals the heat generated by an ampere flowing through a 1 ohm resistor over a one second interval. 

For chemical reactions and phase transformations, the energy absorbed or liberated is measured as heat. The principal unit for reporting heat is the calorie, which is defined as the energy needed to raise the temperature of 1 gram of water at l4.5° C by a single degree. The term kilocalorie refers to 1,000 calories. Another unit of energy is the joule (rhymes with school), which is equal to 0.239 calories. Conversely, a calorie is 4.184 joules. The translation of calories to joules, or kilocalories to kilojoules, is so common in chemical calculations that you should memorize the conversion factors. 

Don t forget that both the calorie and Tins, joule are units of energy in published charts, so you will often have to do a conversion to obtain the unit that you want. 

The joule is a rather small unit of energy. It takes approximately 10,000 joules to raise the temperature of a coffee cup of water by 10°C. Often kilojoules (kJ) are used with 1 kJ equal to 1,000 J. Another popular unit is the calorie, abbreviated with a c. A calorie is the amount of heat necessary to raise one gram of water by 1°C. One calorie is equal to 4.18 joules. The physical unit of a calorie should not be confused with a food calorie. A food calorie, symbolized with a capital C, is equivalent to 1,000 calories. When you eat a piece of cake with 400 Calories, you have actually consumed 400,000 calories. 

Fine, but what are the units of energy Well, that depends. The SI unit of energy is the joule (J), but the calorie (cal) and liter-atmosphere (L atm) are also used. Here s how the joule, the calorie, and the liter-atmosphere are related ... 

In the section on Thermochemistry in the International Critical Tables (see Bichowsky1), the values were recorded in joules, in the hope that thermochemists might come to use this fundamental unit in their calculations and writings. But the attempt to break away from the calorie as a unit in thermochemical and thermodynamical calculations proved to be unpopular and apparently hopeless of accomplishment. In order to satisfy the popular demand for the calorie as a unit in calculations and tabulations, and at the same time depart as little as possible from the fundamental unit of energy, the joule, in terms of which all accurate thermochemical measurements are actually made, we have used in this book a defined calorie, that is, one which has no actual relation whatever, except incidentally and historically, to the heat capacity of water. 

I joule = l volt coulomb (the Si-approved unit of energy) l calorie = 4.184 joules (the so-called mechanical equivalent of heat)... 

SI units have been used throughout the book whenever possible. There are no feet, microns, miles, or tons. Molecular dimensions are given uniformly in nanometers rather than in angstrom units (A lA = 0.1 nm). Likewise the calorie and kilocalorie have been replaced by the SI unit of energy, the joule (J 1 calorie = 4.184 J). 

In this book we use kilocalories in place of the presently recommended (SI) joules for units of energy. As of the date of writing, it is not clear just how general the use of the joule will become among chemists. To convert calories to joules (or kcal to kJ), multiply by 4.184. 

The quantity of energy transferred as heat is measured in joules, J. However, a unit of energy still widely used in biochemistry and related fields is the calorie (cal). The original definition of 1 cal was that it is the energy needed to raise the temperature of 1 g of water by 1°C. The modern definition is... 

An older unit of energy that is still common in physical chemistry circles is the calorie. One calorie was defined to be the amount of energy necessary to raise the temperature of 1 g of water from 14.5 to 15.5 °C. Today, one calorie (thermochemical calorie) is defined to be exactly 4.184 J. The ubiquitous food Calorie (note the capitalization) is a kilocalorie or 1000 cal. 

Scientists must talk to one another in common quantities, units, and symbols. The International Union of Pure and Applied Chemistry (IUPAC) has drawn up tables of chemspeak (Mills et. al., 1993). The Systeme International (SI) unit of energy is the joule (J) and that of power is the watt (IV). In terms of SI base units the former is N m and the latter, J s 1. Older textbooks and scientific papers use the calorie (= 4.184 J) but today s scientists must use the multiplier to be correct when quoting earlier work using this antiquated unit. 

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