The decomposition of HI(g) is represented by the equation 2HI(g)?H2(g)+I2(g) The

Question

The decomposition of HI(g) is represented by the equation

2HI(g)?H2(g)+I2(g)

The following experiment was devised to determine the equilibrium constant of the reaction.

HI(g) is introduced into five identical 400-cm3 glass bulbs, and the five bulbs are maintained at 623 K.The amount of I2 produced over time is measured by opening each bulb and titrating the contents with 0.0150 M Na2S2O3(aq). The reaction of I2 with the titrant is

I2+2Na2S2O3?Na2S4O6+2NaI

Data for the experiment are provided in this table.

28.68

What is the value of Kc for the decomposition of HI at 623 K?

Bulb Initial mass of HI
(g) Time
(hours) Volume of titrant
(mL) 1 0.300 2 20.96 2 0.320 4 27.90 3 0.315 12 32.31 4 0.406 20 41.50 5 0.280 40

28.68

Explanation / Answer

ince the system is at equilibrium, Kc will equal Q.

Q=[Products]^coefficient/[Reactants]^cofficient=Kc

In this case the equation will be:

Q=Kc= [H2][I2]/[HI]^2 *Note that since HI had a coefficient of 2 in the reaction, you raise [HI] to the second power

Now, plug in your values that you solved for:

Q=Kc=[5.378*10^-4][5.378*10^-4]/[4.398*10^-3]2

Q=Kc= 1.5*10^-2

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