Chemical Equilibrium

Chemical Equilibrium is a tool for accurate estimation of concentrations and pressures of the chemical reaction reactants and products at equilibrium. The application derives final, equilibrium parameters based on equilibrium constants (Kc and Kp), initial concentrations and stoichiometric coefficients. Additionally, app calculates reaction quotient "Q" for any given concentrations and stoichiometry (Q in equilibrium is equal to Keq, so can be used for one-click calculation of Kc or Kp when all concentrations or pressures are at equilibrium!). The user may adjust stoichiometric coefficients to fit desired reaction, and set initial concentrations and equilibrium constant to run the calculations.

For a general chemical reaction:

aA + bB <=> cC + dD,

the Reaction Quotient (Q) is defined by:

Q=(C^c*D^d)/(A^a *B^b );

where A, B, C, D – are compounds’ concentrations or pressures and a, b, c, d are stoichiometric coefficient*. Sum of powers determines the reaction order.
*Importantly, actual powers may differ from reaction coefficients, due to overall reaction mechanism complexity.

If Q is not equal to reaction equilibrium constant K (Kc for concentrations and Kp for pressures), then reaction is not at equilibrium and it will proceed (due to difference in forward and reverse reaction speeds) to the direction defined by Q.
If QK – reverse reaction will prevail.

Example:
For given reaction: 2A + 1B <=> 3C + 2D , initial reaction concentrations are Ao=0.1M, Bo=0.2M, Co=0.3M and Do=0.4M and Kc=1 M2.

the Reaction Quotient (Q) is defined by:

Q=(Co^3*Do^2)/(Ao^2*Bo^1 )

Upon loading the data to “Chemical Equilibrium” app, Reaction Quotient is immediately calculated, giving Q= 2.16 M2. Apparently Q>K, suggesting that reaction is too close to the products side and reverse reaction will prevail to bring the reaction back to the equilibrium.

The new equilibrium concentrations of reaction components can be derived from the equation:

Kc=((Co-3x)^3*(Do-2x)^2)/((Ao+2x)^2*(Bo+x))


Apparently, solving this equation is rather demanding task, that turns to be unnecessary, since “Chemical Equilibrium” app immediately returns the answer: Aeq=0.1185M, Beq=0.2092M, Ceq=0.2723M and Deq=0.3815M.


The application features:

To start calculation user is required to fill in stoichiometric coefficients, initial concentrations (pressures) of available components, and equilibrium constant Kc (Kp).

Reaction coefficients are actually representing powers and therefore define reaction order.

To start calculation initially or after updating the concentration or coefficient fields, user is requested to tap Run button!

Significant attention should be paid to concentration, pressure and equilibrium constant units. App automatically changes the set of available units as per order of reaction!

The basic conversions are as follows:

1 M= (1e3) mM
1 atm=101325 Pa

This app is a part of Bio- Chemistry, Chemical Engineering and Pharmacy Lab Pack including several apps dealing with chemical solutions, reaction equilibrium, acid base neutralisation reaction, titration, chemical kinetics and liposome preparation.
The preparation of the desired solutions may be further facilitated by using Chemical Solution Wizard app and deprotonation kinetics may be followed by using Chemical Kinetics app. On the other hand, pH values of the compounds having numerous functional groups (carboxylic and amino-derivatives, like amino acids) can be calculated and plotted by means of Isoelectric Point app.