Compounds calculating moles

Compound Calculated activation energy for ring opening (kcal/mole) disrotatory conrotatory ... 

This problem illustrates the two most common ways of calculating moles of a compound (a) weight divided by mole weight, and (b) molarity times volume in liters. 

First, we need to calculate the mole fraction of the water. Since the solution is 5.0% (w/w), a-100 g sample of the solution would contain 95 g of water and 5 g of sucrose. To find the mole fraction, we need find the moles of each compound. Recall we calculated mole fractions in chapter 6. 

Net ionic equations can be used to calculate mole ratios but often cannot be used direcdy with masses. Although spectator ions do not react, they do have mass, and the molar mass of the compound cannot be determined if all the ions are not specified (Section 10.6). 

The mass of elements in a compound is crucial when solving problems with the Empirical Formula = Simplest Formula empirical formula. First, the number of moles in atoms are found by dividing their masses by their molar masses. Next, the number of moles are either divided by the smallest mole number or, if necessary to calculate mole ratio of elements, multiplied with certain multipliers to get whole numbers for each element. These numbers for different elements provide the empirical formula. 

Calculate the solubility of each of the following compounds in moles per liter and grams per liter. (Ignore any acid-base properties.)... 

In some chemical calculations, you may need to convert from moles of a compound to moles of individual atoms in the compound or from moles of individual atoms in a compound to moles of the compound. The following conversion factors can be written for use in these calculations for the molecule freon. 

The energies of Si-X bond in the (CH3)3SiX compounds (kJ-mole ) calculated by Sanderson method [141] inductive homolytic dissociation of HX compound (Djj x) [143] and Si-X bond calculated by Luo and Benson... 

If we can determine the number of moles of each element in any amount of a substance, we can calculate the molar ratio of these elements in the compound, which can then be simplified to the positive integers that represent the simplest molar ratio. We found in Sections 9.2 and 9.3 that we can calculate moles of a substance from grams. Thus one path to determining the empirical formula for a compound is ... 

Figure 9.19 (a) transformations between different polymorphs or pseudopolymorphs of 9.4, (b) TGA thermograms of y8-[Ni(4-MePy)4(NCS)2] C6H6 (trace 1) and 7-[Ni(4-MePy)4(NCS)2]-2(C6H6) (trace 2) plotted as mass/n v.t. temperatnre (n is the nnmber of moles of each compound calculated from the mass of the final Ni(SCN)2 prodnct). Each experiment starts with crystals of an inclusion compound wetted with benzene (reprinted with permission from Section Key Reference 2004 American Chemical Society). 

Note significant figures and units. Note also that in order to calculate the number of moles in the mass of a compound one must know the formula of the compound. A mole is defined only in terms of the formula of a compound. 

Consider 2.45-g samples of each of the following elements or compounds. Calculate the number of moles of the element or compound present in each sample. 

Possible formulas for the metal bromide could be MBr, MBr2, MBr3, etc. Assuming 100 g of compound, the moles of Br in the compoimd can be determined. From the mass and moles of the metal for each possible formula, we can calculate a molar mass for the metal. The molar mass that matches a metal on the periodic table would indicate the correct formula. 

If 9.60 g of CUSO4 are left after heating 15.01 g of the blue compound, calculate the numba" of moles of H2O originally present in the compound. 

In Chapter 6, we learned how a chemical formula contains conversion factors for converting between moles of a compound and moles of its constituent elements. In this chapter, we have seen how a chemical equation contains conversion factors between moles of reactants and moles of products. However, we are often interested in relationships between mass of reactants and mass of products. For example, we might want to know the mass of carbon dioxide emitted by an automobile per kilogram of gasoline used. Or we might want to know tire mass of each reactant required to obtain a certain mass of a product in a S5mthesis reaction. These calculations are similar to calculations covered in Section 6.5, where we converted between mass of a compound and mass of a constituent element. The general outline for these types of calculations is ... 

The relative masses of the reactants and products of a chemical reaction can be determined from the reaction s coefficients. Recall that an amount of an element or compound in moles can be converted to a mass in grams by multiplying by the appropriate molar mass. We know that 1 mol of hydrogen reacts with 1 mol of chlorine to yield 2 mol of hydrogen chloride. The relative masses of the reactants and products are calculated as follows. 

Mass % composition of compound — Assume 100 g — Grams of each element — X 1/molar mass — Moles of each element Calculate mole ratios Empirical formula... 

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