Consider the reaction: h2(g) + i2(g)-> 2hi(g)
a reaction mixture in a 3.67-l flask at a certain temperature initially contains 0.763 g h2 and 96.9 g i2. at equilibrium, the flask contains 90.4 g hi. calculate the equilibrium constant (kc) for the reaction at this temperature.

K= 616.34

Explanation:

Considering the above reaction, we should consider the initial conditions (when we first have H₂ and I₂ only), and the final conditions (when we have the remaining H₂ and I₂, and the product: HI, all species in equilibrieum)

We also should consider molecular masses:

M H₂ = 2 g/mol

M I₂ = 254 g/mol

M HI = 128 g/mol

In order to calculate the amount of each species at equilibrium:

Initial:

0.763 g H₂

96.9 g I₂

Final (equilibrium):

90.4 g HI

To calculate the final concentration of I₂ and H₂, we use the chemical reaction stoichiometry:

256 g HI > 2 g H₂

90.4 g HI > x = 0.706 g H₂, so at equilibrium: 0.763-0.706= 0.057 g H₂= 0.0285 moles H₂

256 g HI > 254 g I₂

90.4 g HI > x = 89.69 g I₂ , so at equilibirum: 96.9-89.69= 7.21 g I₂ = 0.0284 moles I₂

and then 90.4 g HI = 0.7062 moles HI

Using the volume of the flask, we should calculate the concentration of all species, in molar units (Molar= moles/Lt)

[H₂] = 0.0285/3.67 = 0.00777M

[I₂] = 0.0284/3.67 = 0.00773 M

[HI] = 0.7062/3.67 = 0.1924 M

So: Kc = [HI]² /[I₂][H₂] = (0.1924)² / (0.00777)(0.00773)

Kc = 616.34

Remember that:

- If Kc > 1, this reaction is more run to products

- If Kc<1 , this reaction is more run to reagents

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.