calorie - wikipedia, the free encyclopedia

CalorieFrom Wikipedia, the free encyclopedia

This article is about the units of energy. For other uses, see Calorie (disambiguation).

The name calorie is used for two units of energy.

The small calorie or gram calorie (symbol: cal) is the approximate amount of energy needed to raisethe temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.[1]

The large calorie, kilogram calorie, dietary calorie, nutritionist's calorie, nutritional calorie,Calorie (capital C)[2] or food calorie (symbol: Cal) is approximately the amount of energy needed toraise the temperature of one kilogram of water by one degree Celsius. The large calorie is thus equal to1000 small calories or one kilocalorie (symbol: kcal).[1]

Although these units are part of the metric system, they have been superseded in the International System ofUnits by the joule. One small calorie is approximately 4.2 joules (so one large calorie is about 4.2 kilojoules).The factor used to convert calories to joules at a given temperature is numerically equivalent to the specificheat capacity of water expressed in joules per kelvin per gram or per kilogram. The precise conversion factordepends on the definition adopted.

In spite of its non-official status, the large calorie is still widely used as a unit of food energy. The smallcalorie is also often used for measurements in chemistry, although the amounts involved are typicallyrecorded in kilocalories.

The calorie was first defined by Nicolas Clément in 1824 as a unit of heat,[3] and entered French and Englishdictionaries between 1841 and 1867. The word comes from Latin calor meaning "heat".

Contents

1 Definitions2 Usage

2.1 Nutrition2.2 Chemistry

3 See also4 References

Definitions

The energy needed to increase the temperature of a given mass of water by 1 °C depends on the atmosphericpressure and the starting temperature. Accordingly, several different precise definitions of the calorie havebeen used.

The pressure is usually taken to be the standard atmospheric pressure (101.325 kPa). The temperatureincrease can be expressed as one kelvin, which means the same as an increment of one degree Celsius.

Calorie - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Calorie

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Name Symbol Conversions Notes

Thermochemicalcalorie

calth ≡ 4.184 J

≈ 0.003 964 BTU≈ 1.163 × 10−6 kWh≈ 2.611 × 1019 eV

the amount of energy equal to exactly 4.184joules [4][5][6][7]

4 °C calorie cal4 ≈ 4.204 J

≈ 0.003 985 BTU≈ 1.168 × 10−6 kWh≈ 2.624 × 1019 eV

the amount of energy required to warm one gramof air-free water from 3.5 to 4.5 °C at standardatmospheric pressure.


≈ 0.003 9671 BTU≈ 1.1626 × 10−6 kWh≈ 2.6124 × 1019 eV

the amount of energy required to warm one gramof air-free water from 14.5 to 15.5 °C at standardatmospheric pressure. Experimental values of thiscalorie ranged from 4.1852 J to 4.1858 J. TheCIPM in 1950 published a mean experimentalvalue of 4.1855 J, noting an uncertainty of0.0005 J.[4]


≈ 0.003 964 BTU≈ 1.162 × 10−6 kWh≈ 2.610 × 1019 eV

the amount of energy required to warm one gramof air-free water from 19.5 to 20.5 °C at standardatmospheric pressure.

Mean calorie calmean ≈ 4.190 J

≈ 0.003 971 BTU≈ 1.164 × 10−6 kWh≈ 2.615 × 1019 eV

1⁄100 of the amount of energy required to warmone gram of air-free water from 0 to 100 °C atstandard atmospheric pressure.

International Steamtable calorie (1929)

≈ 4.1868 J

≈ 0.003 9683 BTU≈ 1.1630 × 10−6 kWh≈ 2.6132 × 1019 eV

1⁄860 international watt hours = 180⁄43

international joules exactly.[note 1]

International SteamTable calorie(1956)

calIT ≡ 4.1868 J

≈ 0.003 9683 BTU≈ 1.1630 × 10−6 kWh≈ 2.6132 × 1019 eV

1.163 mW·h = 4.1868 J exactly. This definitionwas adopted by the Fifth International Conferenceon Properties of Steam (London, July 1956).[4]

The figure depends on the conversion factor between international joules and absolute (modern) joules. Using themean international ohm and volt (1.000 49 Ω, 1.000 34 V[8]), the international joule is about 1.000 19 J, using theUS international ohm and volt (1.000 495 Ω, 1.000 330 V) it is about 1.000 165 J, giving 4.186 84 J and4.186 74 J, respectively.

1.


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2. The two definitions most common in older literature appear to be the 15 °C calorie and the thermochemicalcalorie.

Usage

The calorie was first defined specifically to measure energy in the form of heat, especially in experimentalcalorimetry.

Nutrition

In nutritional contexts, the kilojoule (kJ) is the SI unit of food energy, although the kilocalorie is still incommon use.[9] In these contexts, confusingly, the word calorie is very often used for what is actually akilocalorie of nutritional energy. Sometimes, in an attempt to avoid confusion, it is written Calorie (with acapital "C") in an attempt to make the distinction, although this is not universal, and is not widelyunderstood.

In attempts to facilitate comparison, specific energy or energy density figures are often quoted, for example"calories per serving" or "kilocalories per 100 g". Nutritional requirements or intakes are often expressed incalories per day.

Chemistry

In scientific contexts, the term calorie almost always refers to the small calorie. Even though it is not an SIunit, it is still used in chemistry. For example, the energy released in a chemical reaction per mole of reagentis occasionally expressed in kilocalories per mole.[10] Traditionally, this use was largely due to the ease withwhich it could be calculated in laboratory reactions, especially in aqueous solution: a volume of reagentdissolved in water forming a solution, with concentration expressed in moles per liter (1 liter weighing 1 kg),will induce a temperature change in degrees Celsius in the total volume of water solvent, and these quantities(volume, molar concentration and temperature change) can then be used to calculate energy per mole. It isalso occasionally used to specify energy quantities that relate to reaction energy, such as enthalpy offormation and the size of activation barriers. However, its use is being superseded by the SI unit, the joule,and multiples thereof such as the kilojoule.

See also

Basal metabolic rateCaloric theoryConversion of units of energyEmpty calorie

Food energyFrigorieNutrition facts label

ReferencesMerriam-Webster's Online Dictionary Def 1a http://www.merriam-webster.com/dictionary/calorie1.Conn, Carole; Len Kravitz. "Remarkable Calorie". University of New Mexico. Retrieved 30 April 2014.2.Hargrove, James L (2007). "Does the history of food energy units suggest a solution to "Calorie confusion"?".Nutrition Journal 6 (44). doi:10.1186/1475-2891-6-44. Retrieved 31 August 2013.

3.

International Standard ISO 31-4: Quantities and units, Part 4: Heat. Annex B (informative): Other units given forinformation, especially regarding the conversion factor. International Organization for Standardization, 1992.

4.

FAO (1971). "The adoption of joules as units of energy". "The 'Thermochemical calorie' was defined by Rossinisimply as 4.1833 international joules in order to avoid the difficulties associated with uncertainties about the heatcapacity of water (it has been redefined as 4.1840 J exactly)."

5.

Rossini, Fredrick (1964). "Excursion in Chemical Thermodynamics, from the Past into the Future". Pure and6.


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Applied Chemistry 8 (2): 107. doi:10.1351/pac196408020095. Retrieved 21 January 2013. "both the IT calorie andthe thermochemical calorie are completely independent of the heat capacity of water."Lynch, Charles T. (1974). Handbook of Materials Science: General Properties, Volume 1. CRC Press. p. 438.Retrieved 8 March 2014.

7.

International Union of Pure and Applied Chemistry (IUPAC) (1997). "1.6 Conversion tables for units".Compendium of Analytical Nomenclature (PDF) (3 ed.). ISBN 0-86542-615-5. Retrieved 31 August 2013.

8.

"Prospects improve for food energy labelling using SI units". Metric Views. UK Metric Association. 24 February2012. Retrieved 17 April 2013.

9.

Zvi Rappoport ed. (2007), "The Chemistry of Peroxides" (http://books.google.com.br/books?id=4PdYwo25VP8C&pg=PA12), Volume 2 page 12.

10.

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Categories: Units of energy Heat transfer Non-SI metric units

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