How to express a balance constant

How to express a balance constant

It is possible to express a balance constant differently. Everything depends on statements of the problem. This size characterizes the shift of reversible chemical reaction towards formation of initial substances or certain products of this reaction.

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  • handle, paper, calculator


1. Express a balance constant through equilibrium concentration of the substances participating in reaction. Take for the initial size of concentration of substances when the speed of the return and direct reaction are equal. Assume that reversible reaction was entered by substances A and B. Reaction took place in certain conditions with formation of substance C: nA +mB ↔ zC, where n, m, z - coefficients in this equation. Express a constant as follows: Kc = [C] ^z/([A] ^n * [B] ^m) where [C], [A], [B] are the concentration of substances which are in balance.

2. Take isothermal and isobaric processes for a research. In this case express a balance constant by means of Gibbs's equation: ΔGр-и = - RT*lnKc = - 8.31T*2.3lgKc, where R – the universal gas constant equal 8.31; T – reaction temperature, To; lnKc is a natural logarithm of a constant of balance. For convenience transfer it to decimal lgKc. For this purpose increase coefficient by 2.3.

3. Define standard energy of Gibbs for reaction. It is possible to make it, having used the equation for isothermal isobaric process: ΔG = ΔH – T ΔS, where T – reaction temperature, To; ΔH - an enthalpy, kJ/mol; ΔS - entropy, J/(mol hail). Find in the reference book value of an enthalpy and entropy for 1 asking basic chemical compounds. If reaction takes place at a temperature, other than 250C, surely give value of these sizes in a statement of the problem.

4. Find size ΔG reactions at a temperature of 250C. For this purpose put education potentials ΔGобр each of the received reaction products. Then subtract from the sum ΔGобр initial chemicals. Find values of potentials in the reference book.

5. Calculate a balance constant in chemical reaction of gases as a result of which gas turns out too. It pays off through partial pressure of components.

6. If reaction proceeds in solution with the known values of molar concentration of initial substances, then it is possible to calculate a constant by the following formula: Kr = [A] [B] [/B] of. It is applicable to reversible chemical reaction And + B = In +.

Author: «MirrorInfo» Dream Team