Conversions Joule-calorie

For chemical reactions and phase transformations, the energy absorbed or liberated is measured as heat. The principal unit for reporting heat is the calorie, which is defined as the energy needed to raise the temperature of 1 gram of water at l4.5° C by a single degree. The term kilocalorie refers to 1,000 calories. Another unit of energy is the joule (rhymes with school), which is equal to 0.239 calories. Conversely, a calorie is 4.184 joules. The translation of calories to joules, or kilocalories to kilojoules, is so common in chemical calculations that you should memorize the conversion factors. 

The only quantity considered here is the enthalpy of formation, A fH°, at 298.15 K. Data are given in units of kJmol-1. The conversion factor 1 thermochemical calorie = 4.1840 joules was used. 

The use of non-SI units is strongly discouraged. For these units there often do not exist standards, and for historical reasons the same denomination may mean sundry units. For example, it is common practice in theoretical chemistry to state energy values in kilocalories. However, to convert a calorie to the SI unit Joule, there exist different conversion factors ... 

Calculate the conversion factor for changing liter atmosphere to (a) erg, (b) joule, and (c) calorie. Calculate the conversion factor for changing atmosphere to pascal and atmosphere to bar. 

Don t forget that both the calorie and Tins, joule are units of energy in published charts, so you will often have to do a conversion to obtain the unit that you want. 

Although SI is the internationally accepted system of measurement in science, other units are encountered. Useful conversion factors are found in Table 1-4. For example, common non-SI units for energy are the calorie (cal) and the Calorie (with a capital C, which stands for 1 000 calories, or 1 kcal). Table 1-4 states that 1 cal is exactly 4.184 J (joules). 

The requirements set out in this publication and taken mainly from the report on the Nutrient Requirements of Poultry (NRC, 1994) are based on ME (AME), expressed as kilocalories (kcal) or megacalories (Meal)/kg feed. This energy system is used widely in North America and in many other countries. Energy units used in some countries are based on joules (J), kilojoules (kj) or megajoules (MJ). A conversion factor can be used to convert calories to joules, i.e. IMeal = 4.184 MJ 1MJ = 0.239 Meal and 1MJ = 239 kcal. Therefore, the tables of feedstuff composition in this publication show ME values expressed as MJ or kj as well as keal/kg. 

Because the units included in Table 16-1 are in joules and kilojoules, the value of R must be stated in terms of joules, not calories. However, if there is a necessity for expressions in calories, the conversion from joules to calories is 4.184 J = 1 cal. (Note 1 kcal = 1 Cal = 4.184 kJ.)... 

The units used for measuring amounts of energy are the joule or the calorie. Most people are more familiar with the term calorie. This should not be a problem because the simple relationship between the two units is that one calorie is equal to 4.18 joules. This ratio is helpful in setting up problems that ask for a conversion of one unit to another. 

By detinition, one calorie (International Table) is exactly 4.186 8 absolute joules which converts to 1.055 056 X 10 joules for one Btu (International Table). Also, by definition, one calorie (thermochemical) is exactly 4.184 absolute joules which converts to 1.054350 X 103 joules for one Btu (thermochemical). A mean calorie is TSOth of the heat required to raise the temperature of one gram of water at one atmosphere pressure from 0°C to 100°C and equals 4.19002 absolute joules. In all cases, the relationship between calorie and British thermal unit is established by 1 cal/(g. °C) = 1 Btu/(lb. 6SF). A mean Btu, therefore is 7So h of the heat required to raise the temperature of one pound of water at one atmosphere pressure from 32°F to 212°F and equals 1.055 87 X 103 joules. When values are given as Btu or calories, the type of unit (International Table, thermochemical, mean, or temperature of determination) should be given. In all cases for this table, conversions involving jou S are based on the absolute joule. 

CGS units have been used in the text and not SI units, as is the current trend. One important conversion factor, which is required for linking SI and CGS systems is that, one calorie equals 4.186 joules. 

The heat transfer was originally measured in units of calories, where one calorie was defined as the quantity of energy required to raise one gram of pure water from 14.5 to 15.5 °C at one atmosphere. This definition has been supplanted by the introduction of the joule, which represents the energy specified by the conversion factor 1 cal = 4.184 joules. One joule is also equivalent to the energy developed in a circuit by an electric current of one ampere flowing through a resistance of one ohm (driven by a potential difference of one volt) in one second. 

The SI unit of heat and energy is the joule (J). One joule is the equivalent of 0.2390 calories, or one calorie equals 4.184 joules. Table 16-1 shows the relationships among calories, nutritional Calories, joules, and kilojoules (kJ) and the conversion factors you can use to convert from one unit to another. 

Suppose a 10.00-kg mass drops through a height difference of 3.00 m, and the resulting work is used to turn a paddle in 200.0 g water, initially at 15.00°C. The final water temperature is found to be 15.35°C. Assuming that the work done is used entirely to increase the water temperature, calculate the conversion factor between joules and calories. 

Rubber Company Handbook (Weast, 1987) is one of the more commonly available sources. More complete sources, including some with data for a range of temperatures, are listed in the references at the end of the chapter. Note that many tabulations still represent these energy functions in calories and that it may be necessary to make the conversion to Joules (1 cal = 4.1840J). Because of the definition of the energy of formation, elements in their standard state (carbon as graphite, chlorine as CI2 gas at one bar, bromine as Br2 liquid, etc.) have free energies and enthalpies of formation equal to zero. If needed, the absolute entropies of substances (from which AS may be evaluated) are also available in standard sources. 

Convert the energy released in Example 8.2 to joules (recall the conversion factor for calories and joules. Chapter 1). 

The metric system was modified as Systeme International (SI) units (Table 1.6) to prevent some confusion. The SI is based on seven fundamental units—including the mole, meter, kilogram, and second—from which the others are derived. The significant changes for soil chemistry are mole of ion charge for equivalent, siemens for mho, joule for calorie, and pascal for pressure. Table 1.4 summarizes the SI units most frequently encountered in sod chemistry. SI allows easier conversion and communication between disciplines, but unfortunately discards some useful and familiar units, such as angstrom and equivalent,... 

Stuve et al. [78STU/FER] also reported the results of a limited set of drop calorimetry experiments (402.9 to 1001.5 K). The authors fitted an equation to the experimental enthalpy differences such that the heat capacity values meshed smoothly with the value obtained tfom adiabatic calorimetry for 298.15 K. The authors indicated that their equation was applicable, within 0.6 per cent for temperatures between 298 and 1200 K. As discussed below, NiS04 decomposes towards the upper end of this temperature range, and extrapolation of the heat capacities to 1200 K does not seem justified. Conversion of the equation from calorie to joule units leads to ... 

Many readers may be dismayed to find that we do not use only SI units. The fapt is that in geochemistry at the present time this is not possible without a great deal of difficulty, because at least one very important group of contributors to the data of geochemistry, Prediction Central at Berkeley, continues to use calories and related units. Changing all their numbers to SI units simply to preserve SI uniformity in this text would be counter-productive. Students of this subject simply must become accustomed to switching back and forth between calories and Joules, and all their related units. We have tried to include all necessary conversion factors and constants in Appendix A. 

You need to be able to convert between calories and joules. We will consider that conversion process in Example 10.1. 

To caicuiate this energy in calories, we construct the appropriate conversion factor. We want to change from joules to calories, so cai must be in the numerator and J in the denominator, where it cancels ... 

The potential and kinetic energies per unit mass are expressed in units of foot-pounds-force per pound-mass (ft-lbf/lbm) or joules per kilogram (J/kg), Here we have a change in internal energy expressed in Btu per pound-mass or calories per kilogram. In our balance equation, we obviously need some way to interconvert these units so that the sum (u -t- gz + V 2) is in a consistent set of units. All efforts to calculate this conversion factor from... 

This is an experimental fact reproducible in any well-equipped laboratory. Using the conversion factors in Eq. 4.22, we can easily convert all the terms in the energy balance to a common basis. In SI the use of the calorie is discouraged thermal energy quantities are to be expressed only in joules.. However, the use of the calorie (or kilocalorie) is quite common in countries using metric units. Today s student will have to be familiar with its use. 

Table 15.1 summarizes the relationships between calories, nutritional Calories, joules, and kilojoules (kj) and the conversion factors you can use to convert from one unit to another. 

Challenge Define a new energy unit, named after yourself, with a magnitude of one-tenth of a calorie. What conversion factors relate this new unit to joules To Calories ... 

We need the specific heat capacity of iron and the conversion factor between joules and calories. 

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