Reversible reactions endothermic

This reaction is fast it reaches equilibrium quickly. The reaction is also reversible, highly endothermic, and the equilibrium constant is quite large (6 X 10 500°C). 

Because the formation of SO, is exothermic, the reverse reaction is endothermic. Hence, raising the temperature of the equilibrium mixture favors the decomposition of SO, to S02 and 02 as a consequence, the pressures of S02 and 02 will increase and that of SO, will decrease. 

FIGURE 13.27 (a) The activation energy for an endothermic reaction is larger in the forward direction than in the reverse and so the rate of the forward reaction is more sensitive to temperature and the equilibrium shifts toward products as the temperature is raised, (b) The opposite is true for an exothermic reaction, in which case the reverse reaction is more sensitive to temperature and the equilibrium shifts toward reactants as the temperature is raised. 

L-mol 1 -min 1 and the rate constant for the reverse reaction is 392 L-mol 1 -min. The activation energy for the forward reaction is 39.7 kj-mol 1 and that of the reverse reaction is 25.4 kj-mol" (a) What is the equilibrium constant for the reaction (b) Is the reaction exothermic or endothermic (c) What will be the effect of raising the temperature on the rate constants and the equilibrium constant ... 

The reverse reaction, the decomposition of water is highly endothermic ... 

In order to minimize the required reactor volume for a given type of reactor and level of conversion, one must always operate with the reactor at a temperature where the rate is a maximum. For irreversible reactions the reaction rate always increases with increasing temperature, so the highest rate occurs at the highest permissible tepiperature. This temperature may be selected on the basis of constraints established by the materials of construction, phase changes, or side reactions that become important at high temperatures. For reversible reactions that are endothermic the same considerations apply, since both the reaction rate and the equilibrium yield increase with increasing temperature. 

The success of the phase space theory in fitting kinetic energy release distributions for exothermic reactions which involve no barrier for the reverse reaction have led to the use of this analysis as a tool for deriving invaluable thermochemical data from endothermic reactions. This is an important addition to the studies of endothermic reactions described above. As an example of these studies, consider the decarbonylation reaction 11 of Co+ with acetone which leads to the formation of the... 

Figure 5.2 Typical (-rA)-T-fA behavior for reversible reactions (a) exothermic reaction (b) endothermic reaction...

For an endothermic, reversible reaction (such as the dehydrogenation of ethylbenzene), as also shown in Section 5.3 and illustrated in Figure 5.2(b), the rate does not exhibit a maximum with respect to T at constant /, but increases monotonically with increasing T. The rate also decreases with increasing / at constant T, as does the rate of an exothermic reaction. 

Figure 21.8 shows schematically the linear energy equation or operating line added to lines shown in Figure 21.7, both for an exothermic reaction, Figure 21.8(a), and for an endothermic reaction, Figure 21.8(b). Both cases illustrate the limits imposed by the equilibrium constraint for reversible reactions. 

Figure 21.8 Operating lines (AB and CD) from energy equation 21.58 for two-stage (adiabatic) FBCR (a) exothermic reversible reaction (b) endothermic reversible reaction...

It is known that in the vast majority of cases the activation energy E,. of the reverse reaction is very small or even negligible. Using Hammond s postulate [3], it is possible to assume that in the case of endothermic fragmentation the transition state will be much closer to the products than to the initial particle (Fig. 5.14). Thus, the stability of the products influences significantly the efficiency of fragmentation. It is important to consider stability of both products a neutral and a daughter ion. 

They conclude from estimated rates that reaction (8.63) is an insignificant contributor to prompt NO. However, they also point out that the reverse reaction (8.64) is very fast at room temperature and under shock tube conditions. Hence this step is a minor, but nonnegligible contributor to prompt NO and, because of the large endothermicity of reaction (8.64), its importance with respect to reaction (8.61) increases with increasing temperature. 

The reaction of thiyl radicals with silicon hydrides (Reaction 3.18) is the key step of the so called polarity-reversal catalysis in the radical-chain reduction of alkyl halides as well as in the hydrosilylation of olefins using silane-thiol couple (see Sections 4.5 and 5.1) [33]. The reaction is strongly endothermic and reversible (Reaction —3.18). 

At this point, it is to be noted that even when carbon-oxygen bonds are formed by a reaction of an olefin cation-radical with O2, the reaction is rapidly reversible and endothermic (Nelsen 1987). Structures of observable products depend on the rate of reactions other than the interaction with O2. This does not mean that adducts do not form, but that the R -00 product is thermodynamically unstable. The same should be taken into account for 2a—la dithia cation-radicals. 

AN melts at 443 K and begins to gasify above 480 K. The decomposition process of AN is temperature-dependent At low temperatures, i. e. around 480 K, the gasification process of AN is the endothermic (-178 kJ mol" ) reversible reaction represented by[i5]... 

The reversed reaction is, therefore, endothermic. It would require the addition of 8.7 kcal of energy in order to cause the nitrous oxide and water vapor to react to form 1 mole of ammonium nitrate. 

The first reaction is the isomerization from a zero-octane molecule to an alkane with 100 octane the second is the dehydrocyclization of heptane to toluene with 120 octane, while the third is the rmdesired formation of coke. To reduce the rate of cracking and coke formation, the reactor is run with a high partial pressure of H2 that promotes the reverse reactions, especially the coke removal reaction. Modem catalytic reforming reactors operate at 500 to 550°C in typically a 20 1 mole excess of H2 at pressures of 20-50 atm. These reactions are fairly endothermic, and interstage heating between fixed-bed reactors or periodic withdrawal and heating of feed are used to maintain the desired temperatures as reaction proceeds. These reactors are sketched in Figure 2-16. 

Figures—14 Possible region of trajectories for endothermic and for reversible reactions, starting at feed temperature Tj, with heating from the wall at temperature Ti,. Trajectories must be in the shaded region between the adiabatic and isothermal curves and below the equilibrium curve.

It is interesting to note that the exothermic reversible reaction A B is identical to the same endothermic reversible reaction B A. This can be seen by plotting X versus T and noting that the r = 0 equihbrium hue separates these two reactions. In the reaction A B the rate in the upper portion where r < 0 is exactly the reaction B A. We defined all rates as positive quantities, but if we write the reaction as its reverse, both r and AZ/y reverse signs. This is plotted in Figure 5-19. 

Figure 5-19 Plot of X versus 7" for an exothermic reversible reaction A B. The upper portion of this curve where r <0 can be regarded as the endothermic reversible reactions tfi A if the sign of r is reversed or if X is replaced by 1 - X...

The shapes of these curves is plotted in Figure 6-13 for endothermic and exothermic reactions. If AH > 0, then the shape of the X(T) curve is nearly unchanged because the equilibrium conversion is lower at low temperatures, but if AH < 0, then X(T) increases with T initially but then decreases at high T as the reversibihty of the reaction causes X to decrease. However, the multiplicity behavior is essentially unchanged with reversible reactions. 

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