Calorie, definition

A short table of these conversion factors can be found inside the front cover. The American Society for Testing and Materials (ASTM) [10] has prepared a much longer and more useful table, which reveals some additional complexity. For example, there are five different calorie definitions in common use. The largest is 1.002 times the smallest. Only in the most careful work is this small a difference relevant. But if you are doing that kind of work, it is worthwhile to obtain, study, and use the tables in Ref. 10. 

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 ... 

In electrochemistry it is customary to multiply each of those quantities by Avogadro s constant and, when a few additional ions enter the already saturated solution, to speak of the entropy of solution per mole. Let the entropy of one mole of the crystalline solid be denoted by Scr and let Si and S2 denote, respectively, the entropy of the solution before, and after, the entry of the additional solute, both expressed in calories per mole. The total initial entropy is obviously (S + Si) and the final entropy is St. The difference between the final and the initial entropy is by definition AS,at. 

Definition.—The unit quantity of heat is that quantity of heat which raises the temperature of 1 gram of water from 15J° C. to 16 ° C. This is called a calorie. 

Definition.—The heat absorbed in producing a change of physical state or chemical composition of a system, at constant temperature and pressure, is called the latent heat of the given transition, and is measured by the number of calories absorbed during the transition of unit mass of the substance from the initial to the final state. 

Definition.—The Mechanical Equivalent of Heat (J) is the number of ergs of work which, if completely converted into heat, would give rise to one calorie. 

The specific heat capacity commonly has units of J/g-K. Because of the original definition of the calorie, the specific heat capacity of water is 4.184 J/g-K. If the specific heat capacity, the mass, and the change of temperature are all known, the amount of energy absorbed can easily be calculated. 

The ability to strike this kind of balance is a wisdom of the body superior knowledge about calories or food values is not at all necessary, since this feat has doubtless been accomplished millions of times quite unconsciously by people who had no basic nutritional knowledge at all or even the ability or machinery to weigh themselves. What is it that makes it possible to perform this feat We know little about the delicate mechanisms involved we do know definitely that... 

Exothermic Reaction. A reaction in which heat is liberated. It usually proceeds rapidly sometimes explosively. In an endothermic reaction a chemical change proceeds slowly with absorption of a definite number of calories Ref Hackh s (1944), 328-R (Exothermic) 305 R (Endothermic)... 

According to the modern convention, measurable quantities are expressed in SI (System Internationale) units and replace the centimetre-gram-second (cgs) system. In this system, the unit of length is a metre (m, the unit of mass is kilogram (kg) and the unit of time is second (s). All the other units are derived from these fundamental units. The unit of thermal energy, calorie, is replaced by joule (1 J = 107 erg) to rationalize the definition of thermal energy. Thus, Planck s constant... 

With this definition, the quantity of heat q (in calories) is given by... 

The specific heat of any substance is the number of calories required to raise one gram of it 1°C. From our definition of the calorie, it follows that the specific heat of water is 1 cal/g °C. 

Enthalpy-Temperature Relation and Heat Capacity When heal is adsorbed by a substance, under conditions such that no chemical reaction or slate transition occur and only pressure-volume work is done, the temperature. T, rises and the ratio of the heat adsorbed, over the differential temperature increase, is by definition the heat capacity. For a process at constant pressure (following Equation (2)). this ratio is equal to the partial derivative of the enthalpy, and it is called the hear capacity at constant pressure. C,. (usually in calories/degree-mole) ... 

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... 

Consumption of tagatose does not lead to sharp rises in blood glucose or insulin levels and it is, therefore, suitable for diabetic or low glycaemic index foods and drinks. The calorie level is 1.5 g/day and it is also non-cariogenic (oral bacteria only veiy slowly metabolise tagatose). Despite the fact that it is a sugar, and, therefore, should fall outside the FDA definition of tooth-friendly ingredients, the FDA somewhat controversially approved it for use in tooth-friendly products (FDA, 2003). 

The calorie was originally based on 1 g of water. For the purposes of a more exact definition it has been superseded by the joule, so that... 

Other numerical values are exact by definition. For example, the atomic mass scale was established by fixing the mass of one atom of 12C as 12.000 Ou. As many more zeros could be added as desired. Other examples include the definition of the inch (1 in = 2.5400 cm) and the calorie (1 cal = 4.184 00 J). 

How much heat must be added to 1.0 kg of water at 25°C to convert it into steam at 300°C The CP of liquid may be taken as 1 cal/gK = 4.18 J/gK (this is the definition of the calorie.). The heat of vaporization may be obtained from Table 1 of Chapter 3 and gaseous heat capacity data from Table 1 of Chapter 2. 

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