OAT Questions

[Samus2008]

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given 1 mol of Ag and ,4mol S, which is excess (Ag, i know) and how many moles will be left after the reaction is complete?

2Ag+S---->Ag2S

The answer is .2 mol. why?

 

[Brightereyez]

wouldn't S be the limiting reactant n not the excess...
1 mol AgX 1mol S/ 2 mol Ag = 0.5 mol S needed for the reaction, meaning S is in excess

 

[Absolute Vision]

According to the following reaction,

2 Ag+ + S2- à Ag2S

1) Determine the Limiting Reactant (LR):

1 mol Ag+ x (1 mol S2- / 2 mol Ag+ ) = 0.5 mol of S2- are required for the reaction to occur, but since there’s 4 mol of S2- present, the excess reactant is S2-, which makes Ag+ the LR.

2) Use the LR to find the amount of product formed (Ag2S):

1 mol Ag+ x ( 1 mol Ag2S / 2 mol Ag+ ) = 0.5 mol Ag2S is formed

3) Find the amount of excess reactant used:

0.5 mol Ag2S x ( 1 mol S2- / 1 mol Ag2S ) = 0.5 mol of S2- are used up in the reaction.

4) The amount of Sulfide remaining = original amount of S2- -- amount of S2- used up
Amt of sulfide remaining = 4 mol S2- -- 0.5 mol S2- = 3.5 mol of S2- remaining

Summary:

a) The excess reactant is S2-

b) Amt of sulfide remaining = 3.5 mol of S2- remaining