S J2sJnj516

Here entropy is in J/kg-mol-K. The entropy for each gaseous species is

For solid and liquid species the last two terms are zero. Here (5® ) refers to the standard state entropy at temperature T. Typical values for entropy are listed in Tables 5-1 and 5-2.

When a chemical reaction is in equilibrium, an equilibrium constant has been devised which relates the partial pressures and the molar fractions of the species. For example, in the general reaction a\ + bB^cC + dT> (5-18)

a, b, c, and d are the stoichiometric molar concentration coefficients of the chemical molecules (or atoms) A, B, C, and D. The equilibrium constant K, when expressed as partial pressures, is a function of temperature.


Here po is the reference pressure. All pressures are in bars or 105Pa. When a + b = c + d, then Kp is independent of pressure. This condition is not valid for a reaction like Eq. 5-8. In this case the pressure increase will drive the equilibrium reaction into the direction of fewer moles and in the direction of absorbing heat if the temperature is increased. For Eq. 5-8 the hydrogen and oxygen equilibrium relation would be


The equilibrium constant can also be expressed as a function of the molar fractions rij because each partial pressure p„ is equal to the actual pressure p at which the reaction occurs multiplied by its molar fraction (pj = pnj). From Equation 5-19 the equilibrium constant K can also be expressed as c d / \ c+d—a—b

The equilibrium constant for the chemical formation of a given species from its elements is Kf. Typical values of Kf are shown in Tables 5-1 and 5-2. The free energy and the equilibrium constant for the formation of a particular species at standard conditions from its atomic elements are related, namely

Equations 5-19, 5-20, and 5-22 are often used together with mass balance and energy balance relations to solve the simultaneous equations; the equilibrium constant K is primarily used when chemical compounds are formed from their elements.

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Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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