Reactions mass relationships

Liquid-liquid reactors. Examples of liquid-liquid reactions are the nitration and sulfonation of organic liquids. Much of the discussion for gas-liquid reactions also applies to liquid-liquid reactions. In liquid-liquid reactions, mass needs to be transferred between two immiscible liquids for the reaction to take place. However, rather than gas-and liquid-film resistance as shown in Figure 7.2, there are two liquid-film resistances. The reaction may occur in one phase or both phases simultaneously. Generally, the solubility relationships are such that the extent of the reactions in one of the phases is so small that it can be neglected. 

The fifth postulate was very quickly shown to be incorrect, and the first three have had to be modified in the light of later knowledge. However, the first four postulates were close enough to the truth to lay the foundations for a basic understanding of mass relationships in chemical compounds and chemical reactions. 

In this chapter, you learned how to balance simple chemical equations by inspection. Then you examined the mass/mole/particle relationships. A mole has 6.022 x 1023 particles (Avogadro s number) and the mass of a substance expressed in grams. We can interpret the coefficients in the balanced chemical equation as a mole relationship as well as a particle one. Using these relationships, we can determine how much reactant is needed and how much product can be formed—the stoichiometry of the reaction. The limiting reactant is the one that is consumed completely it determines the amount of product formed. The percent yield gives an indication of the efficiency of the reaction. Mass data allows us to determine the percentage of each element in a compound and the empirical and molecular formulas. 

These concepts permit the chemist to examine chemical reactions and determine the mass relationships that are involved. For example, consider the simple pyrotechnic reaction... 

Heterogeneous reactions at a gas-surface interface affect the mass and energy balance at the interface, and thus have an important influence on the boundary conditions in a chemically reacting flow simulation. The convective and diffusive mass fluxes of gas-phase species at the surface are balanced by the production (or destruction) rates of gas-phase species by surface reactions. This relationship is... 

In this chapter, we ll begin learning about how to describe chemical reactions, starting with a look at the conventions for writing chemical equations and at the necessary mass relationships between reactants and products. Because most chemical reactions are carried out using solutions rather than pure materials, we ll also... 

We saw in Section 3.3 that the coefficients in a balanced equation tell the numbers of moles of substances in a reaction. In actual laboratory work, though, it s necessary to convert between moles and mass to be sure that the correct amounts of reactants are used. In referring to these mole-mass relationships, we use the word stoichiometry (stoy-key-ahm-uh-tree from the Greek stoicheion, "element," and metron, "measure"). Let s look again at the reaction of ethylene with HC1 to see how stoichiometric relationships are used. 

We saw in the previous chapter how chemical reactions are described and how certain mass relationships must be obeyed when reactions occur. In this chapter,... 

Fig. 1. The reaction-kinetic relationships between the experimental parameters (duration of experiment, quantities, catalyst components, average molecular mass, solubility in n-heptane, and catalyst yield) for propylene, gas-phase polymerization. Experiment in a I-liter autoclave. Catalyst TiCI3-AlEt3, room temperature, 1 bar, time (r) in hours. From Wisseroth (43).

I he previous chapters showed how the laws of conservation of mass and con--1- servation of atomic identity, together with the concept of the mole, determine quantitative mass relationships in chemical reactions. That discussion assumed prior knowledge of the chemical formulas of the reactants and products in each equation. The far more open-ended questions of which compounds are found in nature (or which can be made in the laboratory) and what types of reactions they undergo now arise. Why are some elements and compounds violently reactive and others inert Why are there compounds with chemical formulas H2O and NaCl, but never H3O or NaCli Why are helium and the other noble gases monatomic, but molecules of hydrogen and chlorine diatomic All of these questions can be answered by examining the formation of chemical bonds between atoms. 

Most of the processes of polymer synthesis are characterized by a high exother-micity combined with a low thermal conductivity coefficient of the monomer-polymer mixture. This relationship between the thermophysical characteristics of the polymerization medium, in combination with the reaction rates observed in actual practice, results in the overheating of the reaction mass and the appearance of a non-uniform distribution of temperature and degree of conversion in space and time. 

Step 1 is a prerequisite to any stoichiometric calculation. We must know the identities of the reactants and products, and their mass relationships must not violate the law of conservation of mass (that is, we must have a balanced equation). Step 2 is the critical process of converting grams (or other units) of substances to number of moles. This conversion allows us to analyze the actual reaction in terms of moles only. 

Every chemical reaction obeys two fundamental laws the law of conservation of mass and the law of conservation of ENERGY. We discussed THE MASS RELATIONSHIPS BETWEEN REACTANTS AND products IN CHAPTER 3 IN THIS CHAPTER WE WILL LOOK AT THE ENERGY CHANGES THAT ACCOMPANY CHEMICAL REACTIONS. 

Often the energy changes that take place dnring chemical reactions are of as mnch practical interest as the mass relationships we discnssed in Chapter 3. For example, combnstion reactions involving fnels such as natural gas and oil are carried out in daily life more for the thermal energy they release than for their products, which are water and carbon dioxide. 

---