Standard enthalpy of combustion

It is difficult to measure the enthalpy change of this reaction. However, standard enthalpies of combustion reactions are easy to measure. Calculate the standard enthalpy of this reaction from the following experimental data ... 

The standard enthalpy of combustion, AH°, is the change in enthalpy per mole of a substance that is burned in a combustion reaction under standard conditions. The products of the combustion of an organic compound are carbon dioxide... 

TABLE 6.4 Substance Standard Enthalpies of Combustion at 25°C (kl-mol ) Formula AH°... 

Standard enthalpies of combustion are listed in Table 6.4 and Appendix 2A. We have seen in Toolbox 6.1 how to use enthalpies of combustion to obtain the standard enthalpies of reactions. Here we consider another practical application— the choice of a fuel. For example, suppose we want to know the heat output from the combustion of 150. g of methane. The thermochemical equation allows us to write the following relation... 

Self-Test 6.15A Calculate the standard enthalpy of combustion of glucose from the standard enthalpies of formation in Table 6.5 and Appendix 2A. 

Self-Test 6.15B You have an inspiration maybe diamonds would make a great fuel Calculate the standard enthalpy of combustion of diamonds from the information in Appendix 2A. 

Elemental sulfur exists in several forms, with rhombic-sulfur the most stable under normal conditions and monoclinic sulfur slightly less stable. The standard enthalpies of combustion of the two forms (to sulfur dioxide) are —296.83 kj-mol 1 and —297.16 kj-mol, respectively. Calculate the enthalpy of the rhombic —> monoclinic transition. 

The standard enthalpy of formation of solid ammonium acetate is —616.14 kJ mol l. Calculate its standard enthalpy of combustion. 

Standard enthalpy of combustion, AH%, is the enthalpy change when one mole of a substance is completely burned in oxygen, under standard conditions. 

Example The standard enthalpy of combustion for methane refers to the reaction CFLug) + 2C>2(g)--> CC>2(g) + 2H20(p... 

Example Calculate the standard enthalpy change for the oxidation of ethanol (C2H5OH) to ethanal (CH3CHO), given the following standard enthalpies of combustion ... 

T. Suzuki, Empirical Relationship Between Lower Flammability Limits and Standard Enthalpies of Combustion of Organic Compounds, Fire and Materials (1994), 18 333-336. 

Ha Hi AHr AH m AH°fi AHS, AHvaP A I see Dimensionless Groups Henry s law constant for species Pa m3 mol-1, equation 9.2-8 enthalpy of reaction for reaction as written, J standard enthalpy of reaction, J standard enthalpy of combustion of species i J mol-1 standard enthalpy of formation of species i, J mol-1 standard molar enthalpy of reaction with respect to species i, J mol-1 enthalpy of vaporization, J mol-1 standard molar enthalpy of activation (TST), J mol-1 initiator (species) inhibitor, inert species... 

Suzuki [Suzuki, Empirical Relationship between Lower Flammability Limits and Standard Enthalpies of Combustion of Organic Compounds, Fire and Materials, 18 333-336 (1994) Suzuki and Koide, Correlation between Upper Flammability Limits and Thermochemical Properties of Organic Compounds, Fire and Materials, 18 pp. 393-397 (1994)] provides more detailed correlations for the UFL and LFL in terms of the heat of combustion. 

This enthalpy has a special name we call it the enthalpy of combustion, and define it as the change in enthalpy accompanying the burning of methane, and symbolize it as A77(CombUstion) or just AHc.ln fact, we rarely perform calculations with AHc but with the standard enthalpy of combustion AH, where the plimsoll symbol implies s.t.p. conditions. 

Table 3.2 Standard enthalpies of combustion A7/c° for a few organic compounds (all values are at 298 K)...

SAQ 3.9 Calculate the standard enthalpy of combustion A He for burning S-D-glucose, C6Hi206. The required values of AHf may be found in Table 3.1. 

A database is not usually a mere collection of values quoted from the literature. It commonly involves some critical assessment of those values and an effort to present a consistent set of data. It is important to clarify what we mean by consistency. Suppose that 40 years ago, somebody made a careful determination of the standard enthalpy of combustion of anthracene (reaction 2.20) and obtained Ac//°(Ci4Hio, cr) = X kJ mol-1. 

Equation 2.26 is also used to evaluate the uncertainty of a standard enthalpy of formation, calculated from a reaction enthalpy. Consider, for instance, a selected value for the standard enthalpy of combustion of ferrocene, A CH° [Fe(r 5-C5H5)2, cr] = —5891.5 4.2 kJ mol-1 [31],... 

In the bomb process, reactants at the initial pressure pi and temperature 7 are converted to products at the final pressure pf and temperature Tf. The primary goal of a combustion calorimetric experiment, however, is to obtain the change of internal energy, Ac//°(7r), associated with the reaction under study, with all reactants and products in their standard states pi = pf = O.IMPa) and under isothermal conditions at a reference temperature 7r (usually 298.15 K). Once AC//°(298.15K) is known, it is possible to derive the standard enthalpy of combustion, AC77°(298.15K), and subsequently calculate the standard enthalpy of formation of the compound of interest from the known standard enthalpies of formation of the products and other reactants. 

Steele et al. [28] have measured the standard enthalpy of combustion of buckminsterfullerene Ceo with bomb calorimetry of solid samples at 298.15 K. They have found a value of 26,033 + 14kJ mol Calculate the standard enthalpy of formation of Ceo and the standard enthalpy of transition from graphite to Cgo-... 

EXAMPLE 6.11 Using standard enthalpies of formation to calculate a standard enthalpy of combustion... 

E° = E°(cathode) — °(anode). standard enthalpy of combustion AHc° The change of enthalpy per mole of substance when it bums (reacts with oxygen) completely under standard conditions, standard enthalpy of formation AH° The standard reaction enthalpy per mole of compound for the compound s synthesis from its elements in their most stable form at 1 atm and the specified temperature, standard entropy of fusion ASfus° The standard entropy change per mole accompanying fusion (the conversion of a substance from the solid state to the liquid state), standard entropy of vaporization ASvap° The standard entropy change per mole accompanying vaporization (the conversion of a substance from the liquid state to the vapor state). 

The standard enthalpy of combustion of benzoic acid (C6H5.COOH) is the IUPAC standard used for calorimetry calibration. 

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