Liter-atmospheres to Calories (L⋅atm to cal)

1 liter-atmosphere equals 24.21725621 calories (rounded).

1 liter-atmosphere = 24.21725621 calories

How to convert liter-atmospheres to calories

To convert liter-atmospheres to calories, multiply the number of liter-atmospheres by 24.21725621. The factor is rounded to 10 significant digits. To go the other way, multiply calories by 0.04129286948 (rounded).

calories = liter-atmospheres × 24.21725621

Example: 10 liter-atmospheres = 242.1725621 calories.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Liter-atmosphere (L⋅atm)

ScientificTraditional unit (still used in some regions)

Exactly 101.325 joules, the work of expanding a gas by one liter against one standard atmosphere.

Pressure times volume has the dimensions of energy, which is why gas chemists found it convenient to multiply a pressure in atmospheres by a volume in litres. One litre-atmosphere is 1 atm acting over 1 L, and the figure used here is 101.325 J. The arithmetic is simple: the standard atmosphere is 101,325 Pa, and a litre is 0.001 cubic metre, so the product is 101.325 pascal-cubic-metres, which is joules.

The atmosphere in this definition goes back to the barometer, being first set by a 760 mm column of mercury at 0 degrees Celsius. The tenth General Conference on Weights and Measures in 1954 fixed it as exactly 1,013,250 dynes per square centimetre, with no dependence on any substance. In 1982 IUPAC moved its reference pressure for substance data to 100 kPa. Expressed in thermochemical calories, one litre-atmosphere is about 24.2 cal.

1 liter-atmosphere = 101.325 joules (exactly).

Sources: Wikipedia: Conversion of units of energy; Wikipedia: Atmosphere (unit); Wikipedia: Calorie

Calorie (cal)

ScientificTraditional unit (still used in some regions)

The thermochemical calorie: exactly 4.184 joules, the energy to raise one gram of water by one degree Celsius. Not the same as the food Calorie, which is a kilocalorie.

Latin calor, meaning heat, supplied the name. Nicolas Clement used it in lectures on heat engines between 1819 and 1824, and by 1852 Pierre Favre and Jean Silbermann applied it to the small unit based on a single gram of water warmed by one degree Celsius. Because the specific heat of water varies slightly with temperature, early calories differed from one laboratory to the next. A mean value near 4.1855 J was published for the 15 degree calorie in 1950, with an uncertainty of 0.0005 J.

Chemists settled the matter by definition. The thermochemical calorie is exactly 4.184 J, which is the figure used here, and NIST lists it with that exact value. The calorie is not an SI unit and is regarded as obsolete, since the ninth General Conference on Weights and Measures in 1948 preferred the joule for heat. One thousand of these calories make a kilocalorie, the larger unit used for food, and a slightly larger calorie, the International Table version of 4.1868 J, is used in steam tables.

1 calorie = 4.184 joules (exactly).

Sources: Wikipedia: Calorie; NIST SP 811, Appendix B.8 (energy conversion factors)

Related conversions

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