Reactants physical state

Nature of the reactants, the temperature, the concentration of the reactants, physical state of the reactants, and catalysts... 

Facile mechanochemical synthesis of thioureas was developed by Strukil et al. (Scheme 3.46) [32], Formation of new thioamide C—N bond was achieved by reaction of aromatic isothiocyanates 166 with aromatic amines (Table 3.20). Addition of small amount of methanol (LAG) was beneficial and the high yields were obtained regardless on the reactant physical state. The whole synthesis was carried out without the use of bulk organic solvents, that is solvent-free mechanosynthesis was quantitative, which voids the use of solvent for purification. Mechanochemical reaction... 

U is essential to specify the physical states of the reactants and products, since there may t>e additional heat changes associated with changes in state. 

Transient, or time-resolved, techniques measure tire response of a substance after a rapid perturbation. A swift kick can be provided by any means tliat suddenly moves tire system away from equilibrium—a change in reactant concentration, for instance, or tire photodissociation of a chemical bond. Kinetic properties such as rate constants and amplitudes of chemical reactions or transfonnations of physical state taking place in a material are tlien detennined by measuring tire time course of relaxation to some, possibly new, equilibrium state. Detennining how tire kinetic rate constants vary witli temperature can further yield infonnation about tire tliennodynamic properties (activation entlialpies and entropies) of transition states, tire exceedingly ephemeral species tliat he between reactants, intennediates and products in a chemical reaction. 

Beginning students are sometimes led to believe that writing a chemical equation is a simple, mechanical process. Nothing could be further from the truth. One point that seems obvious is often overlooked. You cannot write an equation unless you know what happens in the reaction that it represents. All the reactants and all the products must be identified. Moreover, you must know their formulas and physical states. 

Indicate the physical state of each reactant and product, after the formula, by writing... 

The magnitude of AW is dependent not only on the amount of the reactants and products but also on their physical states. 

Pyrometallurgy, the dominant process in chemical metallurgy, uses reactor of different types and designs. In terms of the physical states of the reactants, one generally finds that the different reactions carried out in pyrometallurgy include principally, gas/liquid, liquid/... 

The reaction enthalpy, AHr, is the quantity of heat that is either absorbed by the system (endothermic reaction) or released by the system (exothermic reaction), at constant pressure, as determined by the reaction equation. The reaction enthalpy AHr depends both on the chemical nature of the individual reactants and their physical states. 

Physical state of reactants—Gases and liquids tend to react faster than solids because of the increase in surface area of the gases and liquids versus the solid. 

Kinetics is the study of the speed of reactions. The speed of reaction is affected by the nature of the reactants, the temperature, the concentration of reactants, the physical state of the reactants, and catalysts. A rate law relates the speed of reaction to the reactant concentrations and the orders of reaction. Integrated rate laws relate the rate of reaction to a change in reactant or product concentration over time. We may use the Arrhenius equation to calculate the activation... 

Physical state of reactants—When reactants are mixed in the same physical state, the reaction rates should be higher than if they are in different states, because there is a greater chance of collision. Also, gases and liquids tend to react faster than solids because of the increase in surface area. The more chance for collision, the faster the reaction rate. 

The notion of standard enthalpy of formation of pure substances (AfH°) as well as the use of these quantities to evaluate reaction enthalpies are covered in general physical chemistry courses [1]. Nevertheless, for sake of clarity, let us review this matter by using the example under discussion. The standard enthalpies of formation of C2H5OH(l), CH3COOH(l), and H20(1) at 298.15 K are, by definition, the enthalpies of reactions 2.3,2.4, and 2.5, respectively, where all reactants and products are in their standard states at 298.15 K and the elements are in their most stable physical states at that conventional temperature—the so-called reference states at 298.15 K. 

These are all examples of heterogeneous catalysts as they are In a different physical state to the reactants In the reactions being catalysed. 

The organic solvent is the most important variable as it controls partition and diffusion of the reactants between the two immiscible phases, the reaction rate, solubility, and swelling of permeability of the growing polymer. The solvent should be of such composition so as to prevent precipitation of the polymer before a high molecular weight has been attained. The final polymer should not dissolve in the solvent. The type of solvent will influence the characteristics of the physical state of the final polymer. Solvents such as chlorinated or aromatic hydrocarbons make useful solvents in this system. 

Note that the physical states of reactants and products must be specified as solid (s), liquid (0, gaseous (g), or aqueous (aq) when enthalpy changes are reported. The enthalpy change for the reaction of propane with oxygen is A H = -2043 kj if water is produced as a gas but AEf = -2219 kj if water is produced as a liquid. 

In addition to specifying the physical state of reactants and products when reporting an enthalpy change, it s also necessary to specify the pressure and temperature. To ensure that all measurements are reported in the same way so that different reactions can be compared, a set of conditions called the thermodynamic standard state has been defined. 

As noted previously, the value of AH° given for an equation assumes that the equation is balanced for the number of moles of reactants and products, that all substances are in their standard states, and that the physical state of each substance is as specified. The actual amount of heat released in a specific reaction depends on the amounts of reactants, as illustrated in Worked Example 8.3. 

When we replace the words with symbols for the reactants and the products and include their physical state symbols, we obtain ... 

The chemical properties of solvents have obviously a strong bearing on their applicability for various purposes. The solvents should selectively dissolve the desired solutes and not some others, they should be inactive in the chemical reactions undergone by the solutes, but solvate, again selectively, reactants, transition states, intermediates, and products. These aspects of the behaviour can be achieved by the proper blend of the chemical properties of structuredness, polarity, electron-pair and hydrogen bond donation and acceptance ability, softness, acidity and basicity, hydrophilicity or hydrophobicity, and redox properties, among others. Such chemical characteristics can often be derived from physical properties, but in other cases must be obtained from chemical interactions, for instance by the use of chemical probes ( indicators ). 

The physical states of reactants and products are included where necessary. The symbols used are (s) for solid, (/) for liquid, (g) for gas, and (aq) for aqueous (water) solutions. In the case of sodium chloride formation, the equation is modified accordingly. 

The values for standard heats of reaction may be found in the literature or calculated by thermodynamic methods. The physical state of the reactants and products (e.g. gas, liquid, or solid) must also be specified, if the reaction conditions are such that different states may coexist. For example,... 

Thermodynamics parameters of solution (ASP° P—G,H, S) of reactants (anion salt, MX and receptor, L) and product (complex salt, MLX) combined with corresponding data for the anion complexation process, ACP°, in a given solvent, s-, have been extensively used by us with the aim of deriving the thermodynamics referred to the coordination process, AcoordP°, where reactants and products are in their pure physical state... 

The reaction exergy is usually assumed to consist of a chemical part at the standard state (7 °, p°, and unit activity) and a physical part associated with the physical state of the reaction. The chemical part AE°hemT p is equivalent to the standard affinity A0 of the reaction, and the physical part AEphy is due to the change in temperature, pressure, and concentration of the reactants and products between the standard state and the state at which the reaction proceeds ... 

Heterogeneous catalysts are present in a different physical state from the reactants. A typical heterogeneous catalytic reaction involves a solid surface onto which molecules in a fluid phase temporarily attach themselves in such a way to favor a rapid reaction. Catalytic converters in cars utilize heterogeneous catalysis to break down harmful chemicals in exhaust. 

When chemical equations are combined by addition, the standard heats of reaction may also be added to give, the standard heat of the resulting reaction. This is possible because enthalpy is a property, and changes in it are independent of path. In particular, formation equations and standard heats of formation may always be combined to produce any desired equation (not itself a formation equation) and its accompanying standard heat of reaction. Equations written for this purpose often include an indication of the physical state of each reactant and product, i.e., the letter g, l, or s is placed in parentheses after the chemical formula to show whether it is a gas, a liquid, or a solid. This might seem unnecessary since a pure chemical species at a particular temperature and 1 bar or l(atm) can usually exist only in one physical state. However, fictitious states are often assumed as a matter of convenience. 

In summary, to determine the products and their physical states in a double displacement reaction, you must first deconstruct the reactants. Then switch the cations, and reconstruct the products using proper chemical formulas. You should then balance the chemical equation. You will be given information to determine which of the products, if any, will form a precipitate. Finally, you can write the physical state—(s) or (aq)— of each product and balance the equation. 

Until recently it was a common practice in catalytic science to infer information about the states and changes experienced by the components of a catalyst through knowledge gained of the reactants and products of the catalytic reaction and certain suppositions regarding the types of processes involved. This approach was generally employed because the complex physical states of the catalysts and the sparse concentrations of any metal dopents made it very difficult to directly map and follow the behavior of the catalytic components. 

In addition to the physical state of reactants, it should be remembered that the ideal behavior is encountered only in the gaseous state. As the polymerization processes involve liquid (solution or bulk) and/or solid (condensed or crystalline) states, the interactions between monomer and monomer, monomer and solvent, or monomer and polymer may introduce sometimes significant deviations from the equations derived for ideal systems. The quantitative treatment of thermodynamics of nonideal reversible polymerizations is given in Ref. 54. 

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