Reactants calculating amounts

In cases where the reactants involved are not present in the proper stoichiometric ratios, the limiting reactant will have to be determined and the excess amounts of the other reactants calculated. It is safe to assume that unconsumed reactants and inert components exit with the products in their original forms. Consider the following example. 

Step 1 Convert the mass of each reactant into moles, if necessary, by using the molar masses of the substances. Step 2 Select one of the products. For each reactant, calculate how many moles of the product it can form. Step 3 The reactant that can produce the least amount of product is the limiting reactant. 

The calculated amounts of the catalyst, reactant and solvent (if needed) are then placed in the hydrogenation vessel. Utmost care must be exercised in loading the hydrogenation container with catalysts which are pyrophoric, especially when highly volatile and flammable solvents like ether, methanol, ethanol, cyclohexane or benzene are used. The solution should be added to the catalyst in the container. If the catalyst must be added to the solution this should be done under a blanket of an inert gas to prevent potential ignition. 

Molecular weight control and stabilization are accomplished by addition of a calculated amount of a monofunctional acid such as acetic acid. Diamine loss during polymerization is unavoidable because of its volatility. The loss must be quantitatively taken into account by careful control of process conditions and initial charges of reactants. 

The theoretical yield of a reaction is the maximum amount (moles, mass, or volume) of product that can be obtained from a given amount of reactant. The amounts of products calculated from a given mass of reactant in Section L were all theoretical yields. 

Many chemical reactions, including some of the most important processes in the chemical industry, involve gases. Thirteen million tons of ammonia, for example, are manufactured each year in the United States by the reaction of hydrogen with nitrogen according to the equation 3 H2 + N2 — 2 NH3. Thus, it s necessary to be able to calculate amounts of gaseous reactants just as it s necessary to calculate amounts of solids, liquids, and solutions (Sections 3.4-3.9). 

How do engineers know how much of each reactant they need for a chemical reaction In this chapter, you will use the concept of the mole to calculate the amounts of reactants that are needed to produce given amounts of products. You will learn how to predict the amounts of products that will be produced in a chemical reaction. You will also learn how to apply this knowledge to any chemical reaction for which you know the balanced chemical equation. Finally, you will learn how calculated amounts deviate from the amounts in real-life situations. 

The run began with equimolar (0.1 g mol/L) amounts of sodium hydroxide and ethyl acetate as the reactants. Calculate the overall order of the reaction and the value of the reaction rate constant at 298 K, and write the rate expression for the reaction. 

The concentration of reagents is in most cases chosen to be molar, meaning that it is easy to calculate the relative volumes of the reactant and the reagent needed to complete the reaction. It is not advisable to add the calculated amount of reagent at once to the solution (cf. Chapter II), but the final amount should be equal or more than the equivalent. In some cases it is impossible or impractical to prepare a m reagent thus 0 5 or even 0- 1m reagents have to be used sometimes. It is easy to predict the volume of a particular reagent needed to complete the reaction from the concentrations. Acids and bases are applied mostly in 2m concentrations in order to avoid unnecessary dilution of the mixture. 

When a quantity of product is calculated from a quantity or quantities of reactants, as was done in Sections 10.1 through 10.4 of this chapter, that quantity of product is called the theoretical yield. When a reaction is run, however, less product than the calculated amount is often obtained Some of the product may stay in the solution in which the reaction was run some side reaction may use up some of the reactants or the reaction may be stopped before it is completed. No matter why, the fact is that many reactions produce less product than the calculated quantity that is, the actual yield is less than the theoretical yield. No reaction can produce more than the theoretical yield. The percent yield is defined as 100% times the ratio of the actual yield to the theoretical yield ... 

Aluminium Sulphide. Weigh 1 g of aluminium powder and the calculated amount of finely triturated sulphur, and thoroughly mix the reactants. Spill out the mixture in a mound onto a metal plate and put a magnesium ribbon in the middle so that its upper end protrudes 1-2 cm above the mixture. Ignite the magnesium in a fume cupboard with a lowered glass window ). How can you explain the hydrogen sulphide odour of the aluminium sulphide ... 

Similar calculations are made to determine the success of chemical reactions because most reactions never succeed in producing the predicted amount of product. Although your work with stoichiometric problems so far may have led you to think that chemical reactions proceed according to the balanced equation without any difficulties and always produce the calculated amount of product, this is not the case Not every reaction goes cleanly or completely. Many reactions stop before all of the reactants are used up, so the actual amount of product is less than expected. Liquid reactants or products may adhere to the surfaces of containers or evaporate, and solid product is always left behind on filter paper or lost in the purification process. In some instances, products other than the intended ones may be formed by competing reactions, thus reducing the yield of the desired product. 

Calculate amounts of gaseous reactants and products in a chemical reaction using the gas laws. 

To calculate the conversion rate X of the reactant, the amount withdrawn by the product streams has to be known. As illustrated above, whether component A can reach the extract and/or the raffinate outlet depends on the chosen operating conditions. The ideal TMBR model and the resulting flow rates are shown in Fig. 8.7. Taking into account the external streams and dimensionless flow rates, X can be calculated by Eq. 8.29 ... 

If NaOH and HCl(aq) are combined in anything other than a 1 to 1 mole ratio, one reactant will be in excess. The other will be the limiting reactant. Whenever starting amounts of two reactants are given in a stoichiometry problem, before you can calculate amounts of product you will first have to learn which reactant is the limiting reactant. It will govern how much product forms. 

SAMPLE PROBLEM 3.1 0 Calculating Amounts of Reactant and Product... 

Calculating Amounts of Reactants and Products for a Reaction in Solution... 

The technique for effecting diene syntheses is extremely simple. In favorable cases it suffices to mix calculated amounts of the diene and philodiene in an organic solvent, the reaction then occurring exothermally (17-19 kcal/mole). More sluggish reactions may be carried out at elevated temperatures, e.g., in a pressure vessel or in the melt. However, the exothermal Diels-Alder reaction is an equilibrium reaction and at high temperatures the product may readily redissociate to the reactants nevertheless, a large excess of one of the two components can shift the equilibrium in the desired direction of synthesis. 

Chemistry is mostly about reactions—processes in which groups of atoms are reorganized. So far we have learned to describe chemical reactions by using balanced equations and to calculate amounts of reactants and products. However, there are many important characteristics of reactions that we have not yet considered. 

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