# Chemical Equilibrium and Kinetics for HI Reaction

Chemical Equilibrium and Kinetics for HI Reaction

This Demonstration shows the effect of varying the rate constants and in a classic second-order chemical reaction .

k

f

k

b

H+I⇌2HI

2

2

The concentrations at equilibrium are determined by the initial concentrations and by the equilibrium constant . The rate of approach to equilibrium depends on the forward and backward rate constants and . The initial concentrations of reactants, and are set equal.

K=

c

k

f

k

b

k

f

k

b

[H]

2

0

[I]

2

0

The first plot highlights the evolution of concentrations in time calculated using the following differential equations:

d[HI]

dt

f

2

2

b

2

d[H]

2

dt

d[I]

2

dt

f

2

2

(t)

b

2

The second plot highlights the reaction rate variation as a function of time using:

v=k·[H]·[I]

f

f

2

2

v=k·[HI]

b

b

2

The bottom plot is connected with the solution of the equation

[HI]+2x

0

2

[H]-x[I]-x

2

0

2

0

c

which in turn allows us to obtain the final concentrations using:

[HI]=[HI]+2x

eq

0

[H]=[H]-x

2

eq

2

0

[I]=[I]-x

2

eq

2

0

The latter can only be positive, and this leads to a system of inequations defining the validity domain of , highlighted in green.

x

The intersection with the straight line represents the graphical solution of the equation. Whatever the grade of the equation linked to the reaction, which can be obtained by taking the maximum value between the sum of stoichiometric coefficients of reactants and that of products, there is exactly one solution, because the function in the first term of (1) is always strictly increasing [1].

y=K

c

This Demonstration allows for an assessment of parameters that are usually considered separately. In particular, by varying the time, you can see how the reactant and product concentrations reach equilibrium when the rates of forward and backward reaction become equal.