Chemistry 2e

en · official · sha256:7a66aeeea53142d529b733f59737381c791ff071eb25ae60aec2e59e876d7be5

A mole of substance is that amount in which there are 6.02214076 × 1023 discrete entities (atoms or molecules). This large number is a fundamental constant known as Avogadro’s number (NA) or the Avogadro constant in honor of Italian scientist Amedeo Avogadro. This constant is properly reported with an explicit unit of “per mole,” a conveniently rounded version being 6.022 × 1023/mol.

en · official · sha256:1388313cc207716797f76d9a4dfa0020e205e486a54920ad92f5e01932a2c25c

Consistent with its definition as an amount unit, 1 mole of any element contains the same number of atoms as 1 mole of any other element. The masses of 1 mole of different elements, however, are different, since the masses of the individual atoms are drastically different. The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol) (see Figure 3.5).

en · official · sha256:8b8581efd90e6c4d705136c290a64b38666a7a00d425685218d4e4011db9d905

The mole is an amount unit similar to familiar units like pair, dozen, gross, etc. It provides a specific measure of the number of atoms or molecules in a sample of matter. One Latin connotation for the word “mole” is “large mass” or “bulk,” which is consistent with its use as the name for this unit. The mole provides a link between an easily measured macroscopic property, bulk mass, and an extremely important fundamental property, number of atoms, molecules, and so forth.

en · official · sha256:e07f7f1cb5522e71bca508e07bfd0880eb38ad4fafb2066138d28fe58582446a

Referring to the balanced chemical equation, the stoichiometric factor relating the two substances of interest is 3 molI22 mol Al. The molar amount of iodine is derived by multiplying the provided molar amount of aluminum by this factor:

en · official · sha256:321f9682617be238adf835b822bdbe4876604a55bf02b742a1588e3d0c3499ed

The amount of product that may be produced by a reaction under specified conditions, as calculated per the stoichiometry of an appropriate balanced chemical equation, is called the theoretical yield of the reaction. In practice, the amount of product obtained is called the actual yield, and it is often less than the theoretical yield for a number of reasons. Some reactions are inherently inefficient, being accompanied by side reactions that generate other products. Others are, by nature, incomplete (consider the partial reactions of weak acids and bases discussed earlier in this chapter). Some products are difficult to collect without some loss, and so less than perfect recovery will reduce the actual yield. The extent to which a reaction’s theoretical yield is achieved is commonly expressed as its percent yield: percent yield=actual yieldtheoretical yield×100%

Referencing norms: VykhodDoSotykh

en · official · sha256:2adb4b0816a6cf0676c04b02b05ecffd668c29155e2ab5e7ff3d52ccc2539a6c

Actual and theoretical yields may be expressed as masses or molar amounts (or any other appropriate property; e.g., volume, if the product is a gas). As long as both yields are expressed using the same units, these units will cancel when percent yield is calculated.

Referencing norms: EdinitsaNeNazvana, ye-mass, ye-molar-amount