Entropy change of reaction the entropy ruleofthumb

The entropy change due of reaction (9.5) that converts pure, unmixed reactants to pure, unmixed products, all at the standard pressure of 1 atm, is given by:

ASo = So (products) - So(reactants) = (ds° + cs°) - (as°A + bs°) (9.10)

Just as for the molar enthalpy, the molar entropies in Eq (9.10) can be referenced to the values for the normal physical state of the substances at Tref. so can be obtained from Eqs (3.22) and (3.23) for solids and liquids (see Fig. 3.26), and for gases, from:

Equation (9.10) becomes:

Although Eqs (9.11) applies in principle to gases as well as to condensed phases (as long as CP is constant), the absolute entropy of an ideal gas can be calculated from statistical thermodynamics; the molar entropy of an ideal gas consists of contributions from translation (i.e., motion of the molecules as a whole) and from internal modes of motion, such as rotation and vibration. The translational contribution is much larger than the others, which means that all gas species have approximately the same entropy. The translational entropy of an ideal gas at the standard pressure of 1 atm is given by:

where M is the molecular weight of the gas.

For solids, the third law is s = 0 at T = 0 K, so the absolute entropy can be calculated from:

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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