Consider the reaction H2(g) + Cl2(g) <=> 2 HCl(g), which is exothermic as written. What would be the effect on the equilibrium position of decreasing the volume of the reaction container?

No effect

Explanation:

H2(g) + Cl2(g) <=> 2HCl(g)

Decreasing the volume of the re simply means increasing the pressure. As we can see from the above equation, the total number of moles of the reactants and products are the same. There decreasing the volume ( i.e increaing the pressure) will have no effect on the system and hence the equilibrium position is not affected.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.