Enthalpy exothermic processes

Let us consider the formation of sodium chloride from its elements. An energy (enthalpy) diagram (called a Born-Haber cycle) for the reaction of sodium and chlorine is given in Figure 3.7. (As in the energy diagram for the formation of hydrogen chloride, an upward arrow represents an endothermic process and a downward arrow an exothermic process.)... 

This is an exothermic process, due largely to the large hydration enthalpy of the proton. However, unlike the metallic elements, non-metallic elements do not usually form hydrated cations when their compounds dissolve in water the process of hydrolysis occurs instead. The reason is probably to be found in the difference in ionisation energies. Compare boron and aluminium in Group III ... 

The scale-up of exothermic processes is greatly enhanced through the use of the coefficient of thermal stability. Kafarov [2] defined this as the ratio of the slope (tan ttj) of the line representing the heat removal (due to the heat transfer medium and changes in enthalpy) to the slope (tan ttj) of the line representing heat generation (by the reaction) at the intersection of the two lines when plotted on the T versus Q coordinates. This is expressed as... 

The change in enthalpy of a system is equal to the heat supplied to the system at constant pressure. For an endothermic process, AH > 0 for an exothermic process, AH < 0. 

The addition of an ion to butadiene is clearly an exothermic process in the gas phase due to the formation of aa-bond substituting a rc-bond. The agreement of the reaction enthalpies of the reactions (11) and (12) with equal R (except R = H) is surprising (Table 11). 

Figure 3.8 Born-Haber cycle constructed to obtain the lattice enthalpy A//(E, lce) of sodium chloride. All arrows pointing up represent endothermic processes and arrows pointing down represent exothermic processes (the figure is not drawn to scale)...

The question is Find the molar heat of reaction. This means we need the enthalpy change (AH) in kJ/mol (or J/mol) of glucose. The increase in temperature means that this is an exothermic process (negative enthalpy change). 

True/False. An exothermic process has a negative enthalpy. 

A change in a system or chemical reaction for which there is an absorption of heat (i.e., the process requires heat to proceed). In such systems, AH is a positive value (where H is the enthalpy). See also Enthalpy Exothermic Endogonic Endoergic... 

Electrochemistry, 20 standard potentials for, 22 Electromagnetic spectrum, 45 Electronegativity, 13, 30 Electrons, transfer of, 18 Endothermic process, 23 Energy of activation, 28 Enthalpy, 21 Entropy, 21, 23, 31 Exothermic process, 23... 

The temperature dependence of the equilibrium concentration of a product in a thermodynamically controlled process is determined by the heat (enthalpy change) of the catalyzed reaction. For an exothermic process an increase in temperature... 

Water molecules in the vicinity of hydrophobic polymer chains are highly hydrogen bonded and form ordered structures, called ice-bergs, which are similar to the structure of water molecules in ice [96]. Since the formation of ice-bergs lowers both enthalpy and entropy of mixing, this formation is an exothermic process. This is called hydrophobic interaction. Although the energy of the hydrophobic interaction is on the order of sub kcal/mol to a few... 

Conversely, it s also possible for a process to be favored by enthalpy (exothermic, negative AH) yet be nonspontaneous, because it is strongly disfavored by entropy (negative AS). The conversion of liquid water to ice is nonspontaneous above 0°C, for example, because the process is disfavored by entropy [AS° = -22.0 J/(K mol)] even though it is favored by enthalpy (AH° = -6.01 kj/mol). 

In general, micellisation is an exothermic process and the c.m.c. increases with increasing temperature (see page 86). This, however, is not universally the case for example, the c.m.c, of sodium dodecyl sulphate in water shows a shallow minimum between about 20°C and 25°C. At lower temperature the enthalpy of micellisation given from equation (4.28) is positive (endothermic), and micellisation is entirely entropy-directed. 

The thermal effect of any reactions is mild and does not induce a phase change or a significant change in the temperature of the process units. Hence, the specific enthalpies of the feed and effluent streams, h and h2, of the process units are of comparable magnitude 2 = 2,s/ i,s = 0(1). (Note that this assumption is by no means restrictive rather, it reflects current industrial practice. For example, the use of adiabatic units in highly exothermic processes is avoided for safety reasons, and external cooling systems are preferred. This issue is addressed in detail in Chapter 7.)... 

Formation of an ionic tetracoordinate Si+ complex from an uncharged nucleophile and a functional silane is an exothermic process accompanied by a marked drop in entropy. Many qualitative observations indicated that these complexes are generated more readily at lower temperatures (78,242,252,256). Unfortunately, there are few data on the thermodynamic parameters of complex formation. From the temperature variation of the 29Si resonance position, Bassindale and Stout (252) determined the enthalpy and entropy of the formation of bis(iV,Af-trimethylsilyI)-imidazolium chloride (Table IV, entry 10). A similar procedure permitted Chaudhry and Rummer (242) to determine the enthalpy of formation of complexes of 2-trimethylsilyl-l,l,3,3,-tetramethylguanidine (Table IV, entries 6, 7). 

Sample The complete combustion of butane gas, C4H10, in oxygen gas, Oz, produces C02 and H20. It is a highly exothermic process releasing 2845 kj of heat per mole of butane. Write the balanced thermochemical equation, using all whole-number coefficients. Also, determine the enthalpy change in burning 50.0 g of butane gas. 

---