Question

a reaction X<--->Y occurs in a closed vessel. when it reaches equilibrium at temperature T, the number of molecules changing from X to Y is equal to the number of molecules changing from Y to X

true or false.

Answer 1

OK, equilibrium means that the concentations of products and reactants stays the same. Concentration is a function of the absolute number of molecules and the volume they are in. So when the volume is held constant, as in a closed vessel, you know that the absolute number of molecules stays the same.

That doesn't mean that some X molecules aren't changing into Y molecules and vice versa; it jsut means that the total number of each kind of molecule stays the same.

Is that helpful? Best,