How to find a balance constant

How to find a balance constant

Chemical balance is a condition of a chemical system when the speed of course of direct and return chemical reaction are equal. That is a state at which concentration of initial substances and products of reaction (or their partial pressure) does not change. And the constant of balance Kr is the size defining a ratio between these concentration, or pressure.


1. Let's say you need to calculate a balance constant. If it is about reaction between gases which product is also gas, then the constant of balance pays off through partial pressure of components. For example, consider reaction of catalytic oxidation of dioxide of sulfur to sulfuric anhydride (raw materials for receiving sulfuric acid). It proceeds according to the following scheme: 2SO2 + O2 = 2SO^3.

2. Taking into account the coefficients facing molecules of dioxide of sulfur and sulfuric anhydride, the formula of a constant of balance will look as follows: P^2 SO3/p^2 SO2 x pO2

3. If reaction proceeds in any solution, and molar concentration of initial substances and products, then a formula by which the constant of balance of reversible chemical reaction And + by B = In + is calculated are known to you, will be following: Kr = [A] [B] [/B] of.

4. Calculate a constant of balance of chemical reaction, using the known size of change of energy of Gibbs (you can find these data in chemical reference books). Calculation is made on the following formula: ∆G = - RT lnKp, that is lnKp = - ∆G/RT. Having calculated the size of a natural logarithm Kr, you without effort determine also the size of a constant of balance.

5. When calculating a constant of balance, you remember that the size of change of energy of Gibbs depends only on a final and initial condition of a system, but not on the intermediate stages. In other words, for you it is absolutely indifferent what ways received final substance from initial, change of energy of Gibbs all the same will be the same. Therefore if you cannot determine ∆G for concrete reaction by any reason, it is possible to make calculations for intermediate reactions (important only that they as a result led to formation of final substance necessary to us).

Author: «MirrorInfo» Dream Team