Heat, standard, of formation

The standard enthalpy of formation A// of a compound is defined as the enthalpy change when one mol of the compound is formed from its constituent elements in the standard state. The enthalpy of formation of the elements is taken as zero. The standard heat of any reaction can be calculated from the heats of formation of the products and 

Conversely, the heats of formation of a compound can be calculated from the heats of reaction for use in calculating the standard heat of reaction for other reactions. 

The relationship between standard heats of reaction and formation is given by equation 3.26 and illustrated by Examples 3.8 and 3.9 

A comprehensive list of enthalpies of formation is given in Appendix D. 

As with heats of reaction, the state of the materials must be specified when quoting heats of formation. 

Heat consumed in system by the endothermic reaction = AH° x moles produced = 70,224 X 80 = 5,617,920kJ/h = 5617.9 MJ/h Heat to vaporize feed (gas phase reaction) 

Taking the overall efficiency of the furnace as 70%, the gas rate required 

CHAPTER 3 FUNDAMENTALS OF ENERGY BALANCES AND ENERGY UTILIZATION 

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The standard heat of formation for crystalline H3PO2 is —608.8 kJ/mol (—145.5 kcal/mol) (39). The acid can be prepared by the oxidation of phosphine by iodine and water. 

Table 11.1 Standard heats of formation of some metal silicates at room temperature (from metal oxides)...

Caleulating the heat of reaetion is a multi-step proeess. Beginning with the standard heats of formation at 298 K, first ealeulate the standard heat of reaetion, and then ealeulate AH for the aetual system temperature and pressure. The heat of reaetion at 298 K, AHjgg is usually refeiTed to as the standard heat of reaetion. This ean be readily ealeulated from the standard heats of formation of the reaetion eom-ponents. The standard heat of reaetion is expressed as ... 

Using the standard heats of formation of the reaetion eomponents, ealeulate the standard heat of reaetion and the heat of reaetion at system temperature of 350°C and 1 atm. The reaetion is ... 

STANDARD HEAT OF FORMATION OF COMP. 3, J/g mol STANDARD HEAT OF FORMATION OF COMP. 4, J/g mol ... 

STANDARD HEAT OF FORMATION OF COMP 2, cal/grnol . OOOOOOE + 00... 

STANDARD HEAT OF FORMATION OF COMP 3, cal/gmol -.480800E-1-05... 

Thus, the standard heat of a reaction is obtained by taking tlie difference between tlic standard heat of formation of tlie products and reactants. Once again, if the standard heat of reaction of formation is negative, as is the case of most combustion reactions, then energy is liberated due to tlie chemical reaction. Energy is absorbed if AH° is positive. 

The reverse reaction to give the gaseous species AlX(g) at high temperature accounts for the enhanced volatility of AIF3 when heated in the presence of A1 metal, and the ready volatilization of A1 metal in the presence of AICI3. Using calculations of the type outlined on p. 82 the standard heats of formation of the crystalline monohalides AIX and their heats of disproportionation have been estimated as ... 

Some comparative figures for the standard heats of formation —AH are in Table 16.8. Accordingly, Se03 can not be made by direct oxidation of Se or Se02 and is even hard to make by the dehydration of H2Se04 with P2O5 a better... 

The standard heats of formation AH of gaseous HX diminish rapidly with increase in molecular weight and HI is endothermic. The very small (and positive) value for the standard free energy of formation AGj of HI indicates that (under equilibrium conditions) this species is substantially dissociated at room temperature and pressure. However, dissociation is slow in the absence of a catalyst. The bond dissociation energies of HX show a similar trend from the very large value of 574kJmol for HF to little more than half this (295kJmol ) for HI. 

The standard heat of formation ( AH ) of a chemical compound is the standard heat of reaction corresponding to the chemical combination of its constituent elements to form one mole of the compound, each existing in its standard state at 1 atm and 25°C. It has units of cal/g-mole. 

Find the standard heat of formation of benzene (() given the following heats of combustion data (in kcal/g-mole) at 1 atm and 25°C ... 

Tables of standard free energies of formation at 25°C of compounds and ions in solution are given in Appendix 1 (along with standard heats of formation and standard entropies). Notice that, for most compounds, AG is a negative quantity, which means that the compound can be formed spontaneously from the elements. This is true for water ...

Appendix D lists the following standard heats of formation, all in kJ/mol ... 

Equation can also be used to calculate the standard enthalpy of formation of a substance whose formation reaction does not proceed cleanly and rapidly. The enthalpy change for some other chemical reaction involving the substance can be determined by calorimetric measurements. Then Equation can be used to calculate the unknown standard enthalpy of formation. Example shows how to do this using experimental data from a constant-volume calorimetry experiment combined with standard heats of formation. 

C06-0080. Using standard heats of formation, determine A H for the foiiowing reactions ... 

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