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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.
1.0 kcal 15 (4.2 kJ) calorie (15°C) cal-15 (g-cal-15) cal 15: 1.0 ...
For an overall efficiency of 20%, one watt of mechanical power is equivalent to 18 kJ/h (4.3 kcal/h). For example, a manufacturer of rowing equipment shows calories released from "burning" food as four times the actual mechanical work, plus 1,300 kJ (300 kcal) per hour, [16] which amounts to about 20% efficiency at 250 watts of mechanical output.
The calorie is defined as the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, from a temperature of 14.5 °C, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J .
1 cal / °C⋅g = 1 Cal / °C⋅kg = 1 kcal / °C⋅kg = 4184 J / kg⋅K [20] = 4.184 kJ / kg⋅K . Note that while cal is 1 ⁄ 1000 of a Cal or kcal, it is also per gram instead of kilo gram : ergo, in either unit, the specific heat capacity of water is approximately 1.
The thermochemical calorie is exactly 4.184 J by definition of the International Organization for Standardization (ISO). [4] The thermochemical Btu is calculated by converting from grams to pounds and from Celsius to Fahrenheit. [5] 59 °F (15.0 °C) ≈1,054.80 [6] Used for American natural gas pricing. [3] 60 °F (15.6 °C) ≈1,054.68 [7]
The "grand calorie" (also "kilocalorie", "kilogram-calorie", or "food calorie"; "kcal" or "Cal") is 1000 cal, that is, exactly 4184 J. It was originally defined so that the heat capacity of 1 kg of water would be 1 kcal/°C. With these units of heat energy, the units of heat capacity are 1 cal/°C = 4.184 J/K ; 1 kcal/°C = 4184 J/K.
The "grand calorie" (also "kilocalorie", "kilogram-calorie", or "food calorie"; "kcal" or "Cal") is 1000 small calories, that is, 4184 J, exactly. When heat is measured in these units, the unit of specific heat is usually 1 cal/(°C⋅mol) ("small calorie") = 4.184 J⋅K −1 ⋅mol −1 1 kcal/(°C⋅mol) ("large calorie") = 4184 J⋅K −1 ...