Thermochemical stoichiometry

7 Given a thermochemical equation, or information from which it may be written, calculate the amount of energy released or added for a given amount of reactant or product alternately, calculate the mass of reactant required to produce a given amount of energy. 

If you burn twice as much fuel, it is logical to expect that twice as much energy should be released. The proportional relationships between moles of different substances in a chemical equation, expressed by their coefficients, extend to energy terms. The equation for burning ethane (Equation 10.7) indicates that for every two 

The direct proportionalities between the moles of the reactants and products in a chemical change and the quantity of energy absorbed or released allow these relationships to be used as Per expressions in dimensional-analysis setups. 

See if you can Plan this new kind of problem without hints. 

This is a two-step problem. Once you reach moles of any substance, you can go 

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Thermochemical stoichiometry problems have one less step than other stoichiometry problems because they involve only one substance. There is no mole-to-mole conversion, but rather a mole-to-energy change between the single substance and the AH of the reaction. Watch the sign of AH if the wording of the problem is such that it must be taken into account. 

Mass stoichiometry 2. Thermochemical stoichiometry 3. Limiting reactant 4. Mass stoichiometry 5. Percent yield 6. Thermochemical stoichiometry 7. Limiting reactant 8. Percent yield... 

Pulping additives such as quinoid compounds increase the yield of the pulp mass up to 4% [128]. For commercial application the most promising additives are anthraquinone (AQ) or the more convenient soluble salt of tetrahydroan-thraquinone (THAQ). If AQ or THAQ could be obtained at a price below 2/kg it would find a substantial market as a pulping additive [129], Commercial production of THAQ is now based on the partial thermochemical oxidation of naphthalene. In recent years, however, the lure of the pulp market has promoted several attempts to develop a process for the electrosynthesis of THAQ based on the indirect electrooxidation of naphthalene to naphthaquinone (NQ) with Ce4+, according to the stoichiometry of the reactions 1, 2 and 3. 

Most thermochemical calculations are made for closed thermodynamic systems, and the stoichiometry is most conveniently represented in terms of the molar quantities as determined from statistical calculations. In dealing with compressible flow problems in which it is essential to work with open thermodynamic systems, it is best to employ mass quantities. Throughout this text uppercase symbols will be used for molar quantities and lowercase symbols for mass quantities. 

The objectives of this project are consistent with the objectives (1) and (4) above. The general objective of this project has been to verify a new measurement method to analyse the thermochemical conversion of biofuels in the context of PBC, which is based on the three-step model mentioned above. The sought quantities of the method are the mass flow and stoichiometry of conversion gas, as well as air factors of conversion and combustion system. One of the specific aims of this project is to find a physical explanation why it is more difficult to obtain acceptable emissions from combustion of fuel wood than from for example wood pellets for the same conditions in a given PBC system. This project includes the following stages ... 

A new method to analyse the thermochemical conversion of biomass, in the context of packed-bed combustion, is modelled and verified. The sought quantities of the method are the mass flow and stoichiometry of conversion gas, as well as the air factors of the conversion system and the combustion system. 

Nine studies regarding the thermochemical conversion of packed-beds of biomass have been reviewed. The review is summarized in Table 7 below. The focus of the survey has been on the theories of the methods applied to measure ignition front rate, conversion rate (combustion rate, burning rate), conversion gas stoichiometry, and air factors. 

The preheating of solid fuel and the ash cooling are not included in the thermochemical conversion process. The basic criteria for these four thermochemical conversion reactions are that the solid-fuel convertibles (or moisture, char, volatiles) are converted from the solid phase into the interstitial gas phase and finally to the offgases (Figure 16 and Figure 19). The part of the solid-fuel convertibles that is converted into the interstitial gas phase is defined as the conversion gas [3]. The conversion gas is associated with two important physical properties, namely the empirical stoichiometry [CxHyOz] and the mass flux [kg/m s]. 

The mass flow of the conversion gas, its molecular composition, temperature and stoichiometry, are a complex function of volume flux of primary air, primary air temperature, type of solid fuel, conversion concept, etc. Several workers have tried to mathematically model these relationships, which are commonly referred to as bed models [12,33,14,51,52]. It is an extremely difficult task to obtain a predictive bed model, which is discussed in the introduction of this ew. The review of the thermochemical conversion processes below will outline the complex relationships between these variables and their effect on the conversion gas in sections B 4.4-B 4.6. 

The most important design variables of the conversion system are the mass flow and the empirical stoichiometry of the conversion gas. The conversion gas is the primary product of the thermochemical conversion process in the conversion system. The... 

Chapter 6 therefore deals in detail with this issue, including the latest attempts to obtain a resolution for a long-standing controversy between the values obtained by thermochemical and first-principle routes for so-called lattice stabilities . This chapter also examines (i) the role of the pressure variable on lattice stability, (ii) the prediction of the values of interaction coefficients for solid phases, (iii) the relative stability of compounds of the same stoichiometry but different crystal structures and (iv) the relative merits of empirical and first-principles routes. 

A patent was issued for a Zr-fluorocarbon polymer system (Ref 15) which is said to function much like a Mg-teflon system. The claim was made that it bums progressively, leaving behind a coherent incandescent residue or ash. No published tests of this copcept was found. It can be shown thermochemically, that depending on stoichiometry, Ti functions with equal energy density in this formuation... 

One of the more innovative low-temperature, low-pressure, thermochemical techniques of directly liquefying biomass in water involves the use of 57 wt % aqueous hydriodic acid (HI), the azeotrope boiling at 127°C (Douglas and Sabade, 1985). When treated at 127°C with the azeotrope in a stoichiometric excess of 1.6 to 3.8 of the amount required for complete reduction, cellulose is rapidly hydrolyzed and converted to hydrocarbon-like molecules. The yields reach 60 to 70% at reaction times as short as 0.5 min. The laboratory data are consistent with chemistry in which HI acts to form alkyl iodide intermediates that are then converted to hydrocarbons and molecular iodine by further reaction with HI. The stoichiometry developed from the experimental data with cellulose is... 

Of central importance for reaching attractive efficiencies is the development of a suitable oxide material. A thermochemical analysis of candidate metal oxides which, from their structural properties are suitable for cycling, reveals that without stabilisation of the FeO stoichiometry the achievable conversion of producer gas is not high enough. Stabilisation can be achieved by alloying the oxides with other transition metals. 

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