Session 5: Reaction Quocient (Qc) and Equilibrium Constant (Kc)

In this video I'm going to look at the reaction quotient and the equilibrium constant.

Let's stop with the reaction quotient here we have a reaction we're reactance A and B we act together in a reversible reaction to form products C and D.

Here we have the expression for the reaction quotient cue for the above reaction in the numerator we have the concentration of the product C and D raised to the powers of the coefficients in the denominator we have the concentrations reactance a A and B also raised to the power of the coefficients.

The reaction quotient cue measures the relative amounts of reactants and products at a point in time it is expressed with non equilibrium concentrations.

Now we look at the equilibrium constant KC here is the equilibrium constant expression for reaction in the previous slide just like the expression the reaction quotient cue in the numerator we have the concentrations of the product C&D raised to the power of the coefficients and in needy nominate doubt we have the concentrations of the reactants a NB also raised to the power of the coefficients at equilibrium the concentrations of abc&d a constant and the reaction quotient is known as the equilibrium constant KC

K casey is calculated using equilibrium concentrations of reactants and products next we were right the equilibrium constant expression for this reaction in which hydrogen react with I have been to form hydrogen iodide so here we have the equilibrium constant expression for the above reaction in the numerator we have the concentration of the products raised to the power of the coefficient which in this case is to in the denominator we have the concentrations up the reactance which a hydrogen and Iodine.

And an important point is the equilibrium constant KC has a fixed value for reaction at a specific temperature it is temperature dependent and finally we'll calculate the equilibrium constant KC.

For this reaction at a specific temperature in this table we have data from three experiments for the above reaction the reaction was carried out at 440 degrees C. In this table I've substituted the equilibrium concentrations of the products in the numerator and the reactance in the denominator as you can see the value for the equilibrium constant is almost the same for each experiment.

So for this reaction carried out at 440 degree C the value of the equilibrium constant is around 49 point for next we'll have a look at the magnitude of Kc.

The magnitude of Kc tells us if the equilibrium mixture it will contain mostly products mostly reactance or appreciable amounts of both if the value for Kc is very large for example 10 to the power of 18 then the equilibrium next year it will contain mostly products the reaction almost goes to completion if the value of KC lies between 0.01 and 100 the equilibrium mixture contains appreciable concentrations of reactance and products and if the value of Kc is very small for example 10 to the power of -13 the equilibrium mixture will contain mostly reactants the reaction hardly proceeds