My grandmother left me some silver years ago. I opened the box containing the silver and it had tarnished. Using the equation below, if I had 300 g of silver that had tarnished and 175g H2S, which would be the limiting reactant?

By reaction stoichiometry (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of reactant and product participate in the reaction:

Ag: 2 moles
H₂S: 1 mole
Ag₂S: 1 mole
H₂: 1 mole

Being:

Ag: 107.87 g/mole
H: 1 g/mole
S: 32 g/mole

the molar mass of the compounds participating in the reaction is:

Ag: 107.87 g/mole
H₂S: 2*1 g/mole + 32 g/mole= 34 g/mole
Ag₂S: 2*107.87 g/mole + 32 g/mole= 247.74 g/mole
H₂: 2* 1 g/mole= 2 g/mole

Then, by reaction stoichiometry, the following mass quantities of each compound participate:

Ag: 2 mole* 107.87 g/mole= 215.74 g
H₂S: 1 mole* 34 g/mole= 34 g
Ag₂S: 1 mole* 247.74 g/mole= 247.74 g
H₂: 2* 1 mole* 2 g/mole= 2 g

If you have 175g of H₂S, you can apply the following rule of three: if by stoichiomatry 34 grams of H₂S react with 215.74 grams of Ag, 175 grams of H₂S with how much mass of Ag does it react?

[tex]mass of Ag=\frac{175 grams of H_{2}S* 215.74 grams of Ag}{34 grams of H_{2}S}[/tex]

mass of Ag= 1,110.43 grams

But 1,110.43 grams of Ag are not available, 300 gra s are available. Since you have less mass than you need to react with 175 grams of H₂S, silver Ag will be the limiting reagent.