When a conditions could exist: liquid is in dynamic equilibrium with its vapor at a given temperature, the following (I) There is no transfer of molecules between liquid and vapor
(II) The vapor pressure has a unique value
(III) The opposing processes, (liquid to vapor) and (vapor to liquid), proceed at equal rates
(IV) The concentration of vapor is dependent on time
Which of the above choices are applicable?
a. I
b. II and III
c. I, II, and III
d. II and IV
e. none of these combination

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !