Asample of oxygen gas was found to effuse at a rate equal to two times that of an unknown gas. the molecular weight of the unknown gas is g/mol.

128 g/mol

Explanation:

Graham's law states that  the rate of effusion of a gas is inversely proportional to the square root of the molar mass of its particles.

Mathematically, that is:

Since, you know the ratio of two rates and the molar mass of one gas, you can calculate the molar mass of the other gas.

The molar mass of the oxygen molecule, O₂ = 2×16.0g/mol = 32.0 g/mol.

In the coming equations, I will use 32 g/mol for simplicity of writing.

So, the molecular mass of the unnknown gas is 128 g/mol.

h

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 !