Calorie
calorie | |
---|---|
Unit of | energy |
Symbol | cal |
Conversions | |
1 cal in ... | ... is equal to ... |
joules | 4.182 J |
The calorie is a
with 330 large caloriesIn
In physics and chemistry, the word calorie and its symbol usually refer to the small unit, the large one being called kilocalorie (kcal). However, the kcal is not officially part of the International System of Units (SI), and is regarded as obsolete,[2] having been replaced in many uses by the SI derived unit of energy, the joule (J),[9] or the kilojoule (kJ) for 1000 joules.
The precise equivalence between calories and joules has varied over the years, but in thermochemistry and nutrition it is now generally assumed that one (small) calorie (thermochemical calorie) is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J or 4.184 kJ.[10][11]
History
The term "calorie" comes from
The same term was used for the "small" unit by Pierre Antoine Favre (chemist) and Johann T. Silbermann (physicist) in 1852. This unit was used by U.S. physician Joseph Howard Raymond, in his classic 1894 textbook A Manual of Human Physiology.[15] He proposed calling the "large" unit "kilocalorie", but the term did not catch on until some years later.
In 1879, Marcellin Berthelot distinguished between gram-calorie and kilogram-calorie, and proposed using "Calorie", with capital "C", for the large unit.[2] This usage was adopted by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887, in an influential article on the energy content of food.[2][13]
The small calorie (cal) was recognized as a unit of the
(first suggested by Clausius in 1864, under the name ergon, and officially adopted in 1882).In 1928, there were already serious complaints about the possible confusion arising from the two main definitions of the calorie and whether the notion of using the capital letter to distinguish them was sound.[16]
The joule was the officially adopted SI unit of energy at the ninth General Conference on Weights and Measures in 1948.[17][9] The calorie was mentioned in the 7th edition of the SI brochure as an example of a non-SI unit.[10]
The alternate spelling calory is a less-common, non-standard variant.[12]
Definitions
The "small" calorie is broadly defined as the amount of energy needed to increase the temperature of 1 gram of water by 1 °C (or 1 K, which is the same increment, a gradation of one percent of the interval between the melting point and the boiling point of water).[4][5] The actual amount of energy required to accomplish this temperature increase depends on the atmospheric pressure and the starting temperature; different choices of these parameters have resulted in several different precise definitions of the unit.
Name | Symbol | Conversions | Definition and notes |
---|---|---|---|
Thermochemical calorie | calth | ≡ 4.184 J | The amount of energy equal to exactly 4.184 J (joules) and 1 kJ ≈ 0.239 kcal.[18][19][20][11][a] |
4 °C calorie | cal4 | ≈ 4.204 J
≈ 0.003985 BTU ≈ 1.168×10−6 kW⋅h ≈ 2.624×1019 eV |
The amount of energy required to warm one gram of air-free water from 3.5 to 4.5 °C at standard atmospheric pressure.[b] |
15 °C calorie | cal15 | ≈ 4.1855 J
≈ 0.0039671 BTU ≈ 1.1626×10−6 kW⋅h ≈ 2.6124×1019 eV |
The amount of energy required to warm one gram of air-free water from 14.5 to 15.5 °C at standard atmospheric pressure. CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.[18]
|
20 °C calorie | cal20 | ≈ 4.182 J
≈ 0.003964 BTU ≈ 1.162×10−6 kW⋅h ≈ 2.610×1019 eV |
The amount of energy required to warm one gram of air-free water from 19.5 to 20.5 °C at standard atmospheric pressure.[b] |
Mean calorie | calmean | ≈ 4.190 J
≈ 0.003971 BTU ≈ 1.164×10−6 kW⋅h ≈ 2.615×1019 eV |
Defined as 1⁄100 of the amount of energy required to warm one gram of air-free water from 0 to 100 °C at standard atmospheric pressure.[b] |
International Steam Table calorie (1929) |
≈ 4.1868 J
≈ 0.0039683 BTU ≈ 1.1630×10−6 kW⋅h ≈ 2.6132×1019 eV |
Defined as 1⁄860 "international" watt hours = 180⁄43 "international" joules exactly.[c] | |
International Steam Table calorie (1956) | calIT | ≡ 4.1868 J
≈ 0.0039683 BTU = 1.1630×10−6 kW⋅h ≈ 2.6132×1019 eV |
Defined as 1.163 mW⋅h = 4.1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).[18] |
- ^ The 'Thermochemical calorie' was defined by Rossini simply as 4.1833 international joules in order to avoid the difficulties associated with uncertainties about the heat capacity of water. It was later redefined as 4.1840 J exactly.[22]
- ^ standard atmospheric pressurecan be taken to be 101.325 kPa.
- ^ The figure depends on the conversion factor between "international joules" and "absolute" (modern, SI) joules. Using the mean international ohm and volt (1.00049 Ω, 1.00034 V),[21] the "international joule" is about 1.00019 J, using the US international ohm and volt (1.000495 Ω, 1.000330 V) it is about 1.000165 J, giving 4.18684 and 4.18674 J, respectively.
The two definitions most common in older literature appear to be the 15 °C calorie and the thermochemical calorie. Until 1948, the latter was defined as 4.1833 international joules; the current standard of 4.184 J was chosen to have the new thermochemical calorie represent the same quantity of energy as before.[19]
Usage
Nutrition
In the
In the European Union, on nutrition facts labels, energy is expressed in both kilojoules and kilocalories, abbreviated as "kJ" and "kcal" respectively.[27]
In China, only kilojoules are given.[28]
Food energy
The unit is most commonly used to express food energy, namely the specific energy (energy per mass) of metabolizing different types of food. For example, fat (triglyceride lipids) contains 9 kilocalories per gram (kcal/g), while carbohydrates (sugar and starch) and protein contain approximately 4 kcal/g.[29] Alcohol in food contains 7 kcal/g.[30] The "large" unit is also used to express recommended nutritional intake or consumption, as in "calories per day".
Chemistry and physics
In other scientific contexts, the term "calorie" and the symbol "cal" almost always refers to the small unit; the "large" unit being generally called "kilocalorie" with symbol "kcal". It is mostly used to express the amount of energy released in a chemical reaction or phase change, typically per mole of substance, as in kilocalories per mole.[32] It is also occasionally used to specify other energy quantities that relate to reaction energy, such as enthalpy of formation and the size of activation barriers.[33] However, it is increasingly being superseded by the SI unit, the joule (J); and metric multiples thereof, such as the kilojoule (kJ).[citation needed]
The lingering use in chemistry is largely due to the fact that the energy released by a reaction in
See also
- Basal metabolic rate
- Caloric theory
- Conversion of units of energy
- Empty calorie
- Food energy
- A calorie is a calorie
- Nutrition facts label
- British Thermal Unit
References
- ^ ISBN 9780122004001
- ^ a b c d e f Allison Marsh (2020): "How Counting Calories Became a Science: Calorimeters defined the nutritional value of food and the output of steam generators Archived 2022-01-21 at the Wayback Machine" Online article on the IEEE Spectrum Archived 2022-01-20 at the Wayback Machine website, dated 29 December 2020. Accessed on 2022-01-20.
- ^ a b "Definition of Calorie". Merriam-Webster. 1 August 2017. Retrieved 4 September 2017.
- ^ a b "Cambridge Dictionary: calorie". Retrieved 9 November 2019.
- ^ a b "Definition of calorie noun from the Oxford Advanced American Dictionary". Retrieved 9 November 2019.
- ^ a b c U. S. Food and Drug Administration (2019): "Calories on the Menu - Information for Archived 2022-01-20 at the Wayback Machine". Online document at the FDA Website Archived 2013-09-15 at the Wayback Machine, dated 5 August 2019. Accessed on 2022-01-20.
- ^ a b c U. K. National Health Service (2019): "What should my daily intake of calories be? Archived 2022-01-21 at the Wayback Machine". Online document at the NHS website Archived 2020-05-02 at the Wayback Machine, dated 24 October 2019. Accessed on 2022-01-20.
- ^ a b Conn, Carole; Len Kravitz. "Remarkable Calorie". University of New Mexico. Retrieved 1 March 2019.
- ^ a b Bureau International des Poids et Mesures (2019): The International System of Units (SI) Archived 2022-01-20 at the Wayback Machine, 9th edition.
- ^ a b Bureau International des Poids et Mesures (1998): The International System of Units (SI) Archived 2022-01-20 at the Wayback Machine, 7th edition.
- ^ a b United Nations Food and Agriculture Organization (2003): "FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors Archived 2010-05-24 at the Wayback Machine". Accessed on 21 January 2022.
- ^ a b ""Calorie."". Merriam-Webster.com Dictionary. Retrieved 2024-03-20.
- ^ PMID 18086303.
- ^ a b JL Hargrove, "history of the calorie in nutrition", J Nutr 136/12 (December 2006), pp. 2957–2961.
- ^ Joseph Howard Raymond (1894): A Manual of Human Physiology: Prepared with Special Reference to Students of Medicine Archived 2022-01-21 at the Wayback Machine. W.B. Saunders, 376 pages.
- S2CID 4068300.
- ^ "Resolution 3 of the 9th CGPM (1948): Triple point of water; thermodynamic scale with a single fixed point; unit of quantity of heat (joule)", BIPM. Archived 2021-06-14 at the Wayback Machine.
- ^ a b c International Standard ISO 31-4: Quantities and units, Part 4: Heat. Annex B (informative): Other units given for information, especially regarding the conversion factor. International Organization for Standardization, 1992.
- ^ . Retrieved 21 January 2013.
both the IT calorie and the thermochemical calorie are completely independent of the heat capacity of water.
- ISBN 9780878192342. Retrieved 8 March 2014.
- ISBN 0-86542-615-5. Archived(PDF) from the original on 2003-10-16. Retrieved 31 August 2013.
- FAO (1971). "The adoption of joules as units of energy".
- ^ Nutrition, Center for Food Safety and Applied (7 March 2022). "Changes to the Nutrition Facts Label". FDA.
- ^ "Prospects improve for food energy labelling using SI units". Metric Views. UK Metric Association. 24 February 2012. Retrieved 17 April 2013.
- ^ "SI Conventions". National Physical Laboratory. Retrieved 8 February 2016.
- ISBN 978-0-323-40206-4.
- ^ "EU Regulation No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers". EUR-Lex. Retrieved 18 April 2022.
- ^ USDA (2013). "China, General Rules for Nutrition Labeling of Prepackaged Foods" (PDF). Retrieved 18 April 2022.
- ^ "How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?". Scientific American. Retrieved 8 September 2017.
- ^ "Calories - Fat, Protein, Carbohydrates, Alcohol. Calories per gram". Nutristrategy.
- PMID 16389240.
- ^ Zvi Rappoport ed. (2007), "The Chemistry of Peroxides", Volume 2 page 12.
- ISBN 9780120954407. Retrieved 5 September 2017.