Caloric chemical reactions

Calorising Also spelled Calorizing. A proprietary process for protecting the surface of iron or steel by applying a layer of aluminum. Several methods of application may be used dipping, spraying, or chemical reaction with aluminum chloride. See also metal surface treatment. 

In the early 1800s, there was a decided difference of opinion among chemists about the merits of pursuing philosophical chemistry. For Dalton, like the young Dumas, the cause of chemical reactions and behavior lay in elementary atoms and forces of attraction and repulsion lying in atoms and in the clouds of caloric surrounding them.29 Similarly, for Berzelius,... 

Lavoisier summarized his ideas developed over the previous twenty years in his seminal 1789 book Traite Elementaire de Chimie (Elements of Chemistry). This work presented his findings on gases and the role of heat in chemical reactions. He explained his oxygen theory and how this theory was superior to phlogiston theory. Lavoisier established the concept of a chemical element as a substance that could not be broken down by chemical means or made from other chemicals. Lavoisier also presented a table of thirty-three elements. The thirty-three elements mistakenly included light and caloric (heat). Lavoisier put forth the modern concept of a chemical reaction, the importance of quantitative measurement, and the principle of conservation of mass. The final part of Lavoisier s book presented chemical methods, a sort of cookbook for performing experiments. 

The method described above allows us to calculate the location of the flame surface for supply of any amount of gas and air for any low caloricity of the gas. This calculation is based on the assumption of a large chemical reaction rate at the flame surface (and at the combustion temperature), which leads to a narrow zone in which the chemical reaction runs and to the possibility of considering the flame a geometric surface. 

The instrument that Lavoisier used with the greatest success to demonstrate the truth of his system was the balance, an instrument with a beam pivoting on a central knife-edge, with a scale pan at each end. Chemical substances are neither created nor destroyed during reactions, and this truth can be shown to hold for any substance that has weight. We shall see later that Lavoisier needed a different instrument to try to show that caloric, the matter of heat, behaved as a simple substance in chemical reactions. This was a problem precisely because caloric had no weight. 

Alas, thermal phenomena in chemical reactions are more complicated than allowed for in the simple model of combination with caloric or release of caloric. Not until the development of chemical thermodynamics and thermo-... 

Even as Lavoisier demolished phlogiston, he postulated a new gaseous simple substance or element called caloric—the element of heat (see Lavoisier s Table of Elements, Figure 202). Lavoisier had fully explained mass transformation in chemical reactions. The nature of energy transformations remained a mystery. Caloric could be transferred from a warmer body to a cooler body without chemical change. However, Lavoisier also posited that oxygen the element was a com-... 

The study of affinity from another aspect was contained in the attempts to find a measure of the chemical forces by the amount of heat given out in a chemical reaction. The importance of thermal phenomena in chemical reactions was realised by Lavoisier and Laplace (1784), who laid the foundations of thermochemistry (see Vol. Ill, p. 426). They assumed that the amount of heat evolved in a chemical reaction is equal to that absorbed in the reverse reaction, and measured some specific heats and the amount of heat evolved in reactions, in combustion, and respiration. Persoz regarded both Lavoisier s caloric theory of combustion and Berzelius s electrochemical theory (see p. 169) as unsatisfactory, and concluded that there is no means of explaining the heat developed in chemical reactions . 

For process simulators, a more sophisticated way is chosen which makes sure that the caloric properties are consistent even if chemical reactions occur. This is the case if the standard enthalpy of formation Ab° is taken as the reference point, This is explained in detail in the Section 3.1,5 and Chapters 6 and 12, The standard enthalpy of formation refers to the standard conditions To = 298,15 K and Po = 101325 Pa in the state of ideal gases (see Section 2.3), Therefore, the reference point for the specific enthalpy for a pure component is... 

Black evidently thought that supplying latent heat involved chemical reactions which, using Lavoisier s term caloric , might be represented by... 

In many reactions, AH and AG are similar in magnitude (see B1, for example). This fact is used to estimate the caloric content of foods. In living organisms, nutrients are usually oxidized by oxygen to CO2 and H2O (see p. 112). The maximum amount of chemical work supplied by a particular foodstuff (i. e., the AG for the oxidation of the utilizable constituents) can be estimated by burning a weighed amount in a calorimeter in an oxygen atmosphere. The heat of the reaction increases the water temperature in the calorimeter. The reaction heat can then be calculated from the temperature difference AT. 

Heat effects as such are rather unspecific, especially if the nature of the reactions taking place in the calorimeter is not known. The combination of thermal analysis with chemical analysis (for example with a thermobalance (DTG) or a mass spectrometer which register the rate of advancement of the reaction) enables us to arrive at specific caloric data (i.e., AH/A nt). Absolute values of AH are obtained by calibration only. 

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