Question

Is the following statement true or false? Justify your answer. "The reactant that is present in the lesser amount is always the limiting reagent." Problems 1) Consider the synthesis of water shown in model 3. A container is filled with 100,0 g of H2 and 50.0 g of Oz. (a) Which reactant is the limiting reactant? Show your work in detail. (b) What mass of water can be produced? Is this the theoretical yield or the actual yield? (c) Which reactant is present in excess and how much of this reactant remains unreacted after the reaction is complete? (d) This experiment only produced 104.0 g of water in the laboratory Determine the percentage yield of this reaction.

Answer 1

1) balanced reaction is

2H2 ( g ) + O2 ( g ) $\rightarrow$ 2 H2O ( l )

moles of H2 = 100 gm / 2 gm mol^-1 = 50 mol

moles of O2 = 50 gm / 32 gm mol^-1 = 1.56 mol

since according to balanced reaction 1 mol of O2 reacts with 2 mol of H2

so 1.56 mol of O2 needs 2 x 1.56 mol H2 = 3.12 mol H2

but moles of H2 given are 50 so excess reagent is H2 ( g ) and limiting reagent is O2 ( g ) .

all the calculations are based on limiting reactant.

2) moles of water produced = moles of H2 reacted = 2 x moles of O2 reacted = 3.12 mol H2O ( l )

weight of water produced = 3.12 mol x 18 gm mol^-1 = 56.16 gm

it is theoretical yield of reaction

3)H2 is excess reagent

moles left = 50 - 3.12 = 46.88 mol

weight left = 46.88 mol x 2 gm mol^-1 = 93.76 gm

4)percentage yield of reaction is = ( actual yield / theoretical yield ) x 100

According to question % yield = (104 x 100 ) / 56.16 = 185.185

( which looks superficial )