Under standard conditions, which of the following operations results in a spontaneous chemical reaction taking place? a. A piece of aluminum metal is placed in an aqueous solution of potassium nitrate. b. Iodine crystals are added to an aqueous solution of sodium chloride. c. A piece of silver metal is placed in an aqueous solutions of copper(II) nitrate. d. Chlorine gas is bubbled through an aqueous solution of sodium bromide. e. At least two of the above (A-D) result in a spontaneous chemical reaction

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 !

the answer is d. 74.02

c. electrical charges of ionic bonds.