Processes endothermic

Most metals react exothermically with oxygen to form an oxide. Figure 3.4 shows how the value of AG for this process varies with temperature for a number of metals (and for carbon), and it can be seen that in all cases AG becomes less negative as the temperature is increased. However, the decomposition of these metal oxides into the metal and oxygen is an endothermic process, and Figure 3.4 shows that this process does not become even energetically feasible for the majority of metals until very high temperatures are reached. 

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.)... 

Bonding of Hydrogen to Other Atoms. The hydrogen atom can either lose the 1 valence electron when bonding to other atoms, to form the ion, or conversely, it can gain an electron in the valence shell to form the hydride ion, (see Hydrides). The formation of the ion is a very endothermic process ... 

The feedstocks to the styrene process are ethylbenzene and superheated steam, and a typical unit produces hydrogen, small amounts of light hydrocarbons and carbon dioxide as gaseous products, and a Hquid product stream containing 95% + styrene and minor amounts of toluene, benzene, and other aromatics. In an integrated plant, the benzene can be recycled to the ethylbenzene unit, while the other by-products usually are consumed as fuel for the highly endothermic process. 

Because the evaporation of the solvent is an endothermic process, heat must be suppHed to the system, either through conduction, convection, radiation, or a combination of these methods. The total energy flux into a unit area of coating, is the sum of the fluxes resulting from conduction, convection, and radiation (see Heat exchange technology, HEAT thansfer). 

Alumina trihydrate - to achieve reduclion of heal by cooling through an endothermic process that decomposes Ihe flame... 

In the petrochemical industry close to 80% of reactions are oxidations and hydrogenations, and consequently very exothermic. In addition, profitability requires fast and selective reactions. Fortunately these can be studied nowadays in gradientless reactors. The slightly exothermic reactions and many endothermic processes of the petroleum industry still can use various tubular reactors, as will be shown later. 

Environmental conditions under which solvent release from the adhesive on the substrate is produced must be carefully controlled. Humidity is critical because loss of heat due to solvent evaporation may allow attainment of the dew point (the evaporation of the solvent is an endothermic process), and then condensation of water on the adhesive can result. This phenomenon is often called moisture blooming. The presence of water on the adhesive film causes a detrimental effect because the autoadhesion of rubber chains is greatly inhibited. Therefore, humidity must be controlled and avoided by increasing the temperature during solvent evaporation. 

The icicle melts as heat is absorbed by the ice — an endothermic process. 

Endothermic and exothermic processes. On the left the icicle melts as heat is absorbed by the ice, an endothermic process. On the right, steam rises from boiling water, an exothermic process. 

Determine whether the statements given below are true or false. Consider an endothermic process taking place in a beaker at room temperature. 

The effect of a temperature change on solubility equilibria such as these can be predicted by applying a simple principle. An increase in temperature always shifts the position of an equilibrium to favor an endothermic process. This means that if the solution process absorbs heat (AHsoin. > 0), an increase in temperature increases the solubility. Conversely, if the solution process is exothermic (AH < 0), an increase in temperature decreases the solubility. 

Dissolving a solid in a liquid is usually an endothermic process heat must be absorbed to break down the crystal lattice. 

Endothermic process A process in which heat is absorbed by a system AH is positive for an endothermic reaction, 266... 

Endothermic process Processes that absorb heat from the surroundings. 

There have been few attempts to classify decomposition reactions of solids. Gamer [64] made only the broad distinction between endothermic processes (which are often reversible and include dissociation of crystalline hydrates and carbonates) and exothermic processes (which are usually... 

A process that releases heat into the surroundings is called an exothermic process. Most common chemical reactions—and all combustions, such as those that power transport and heating—are exothermic (Fig. 6.8). Less familiar are chemical reactions that absorb heat from the surroundings. A process that absorbs heat is called an endothermic process (Fig. 6.9). A number of common physical processes are endothermic. For instance, vaporization is endothermic, because heat must be supplied to drive molecules of a liquid apart from one another. The dissolution of ammonium nitrate in water is endothermic in fact, this process is used in instant cold packs for sports injuries. 

We can therefore report that AH = —208 kj because the enthalpy of the reaction mixture decreases by 208 kj in this reaction (Fig. 6.18). An endothermic process absorbs heat, and so when ammonium nitrate dissolves in water the enthalpy of the system increases (Fig. 6.19). Note that AH < 0 for exothermic reactions, whereas AH > 0 for endothermic reactions. 

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. 

FIGURE 7.17 (a) In an exothermic process, heat escapes into the surroundings and increases their entropy, (b) In an endothermic process, the entropy of the surroundings decreases. The red arrows represent the transfer of heat between system and surroundings, and the green arrows indicate the entropy change of the surroundings. 

The initial kinetic energy of 0 ions produced by dissociative attachment in 02 at an electron energy of 6.9 e.v. may be determined from Equation 4 to be 1.64 e.v. using values of 1.465 e.v. (1) for A(0) and 5.09 e.v. (7) for D(O—O). The residence time for 0 ions calculated from Equation 1 is 6.0 X 10 7 sec. at 10 volts repeller potential. Rate constants for Reaction 6 determined from data at varying Vr are shown in Table I and are seen to increase sharply with increasing repeller potential, as expected for an endothermic process. 

Traditionally, the steam reforming reactor has a tubular design in which vertical tubes, loaded with catalyst, are surrounded by furnaces to supply the heat required for the strongly endothermic process, see Fig. 8.2. Combustion of natural gas supplies the heat to the tubes. 

The dehydrogenation of cyclohexane to benzene is an endothermic process (206kjmol ),e.g.,performedat200°C.Theequilibriumconversionamountsto 18.9%[127]. 

Many of the cold packs sold in stores use this endothermic process. A cold pack usually contains a flimsy plastic bag of solid ammonium nitrate inside a larger package filled with water. When punched, the inner bag ruptures. This releases the ammonium nitrate, which dissolves and produces a chilled pack to relieve pain and swelling in aching joints. 

Read the entire laboratory activity. Form a hypothesis about how to distinguish exothermic and endothermic processes. Record your hypothesis on page 123. 

At a given ambient water vapor pressure (usually the level found in the open atmosphere), the temperature of the material is raised so that the equilibrium water vapor pressure over the hydrated material is higher than the ambient water vapour pressure. Generally, heating up to 400 °C is sufficient to remove all the water of crystallization from materials. This removal of water yields a material which may contain some more strongly bound water. To remove this water, the material requires to be heated to a higher temperature (400-600 °C) so that the equilibrium water vapour pressure exceeds the ambient water vapour pressure. For near-complete removal of the last traces of water, temperatures as high as 1000 °C may be required. In addition to the heat required to raise the temperature of the material, heat is also required for the evaporation of water, which is an endothermic process. The enthalpy of evaporation increases as the water content, and hence the equilibrium water vapor pressure, decreases. 

Qs = heat generated in the system. If heat is evolved (exothermic processes) Qs is taken as positive, and if heat is absorbed (endothermic processes) it is taken as negative. Qp = process heat added to the system to maintain required system temperature. 

B. Endothermic processes a penalty of 0.2 is applied to reactors, only. It is increased to 0.4 if the reactor is heated by the combustion of a fuel. 

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