Question

What is the theoretical yield of Li3N in grams when 12.8 g of Li is heated with 34.9 g of N2?

Answer 1

Answer:- 21.4 grams of $Li_3N$ are formed.

Solution:- The balanced equation is:

$6Li+N_2\rightarrow 2Li_3N$

From this equation, lithium and nitrogen reacts in 6:1 mol ratio. Limiting reactant gives the theoretical yield of the product. We will calculate the grams of the product for the given grams of both the reactants and see which one of them gives the limited amount of the product. This limited amount of the product will be the theoretical yield.

The molar mass of Li is 6.94 gram per mol and for $N_2$ It is 28.02 gram per mol. The molar mass of $Li_3N$ is 34.83 gram per mol. The calculations for the grams of the product for given grams of both the reactants are shown below:

$12.8gLi(\frac{1molLi}{6.94gLi})(\frac{2molLi_3N}{6molLi})(\frac{34.83gLi_3N}{1molLi_3N})$

= $21.4gLi_3N$

$34.9gN_2(\frac{1molN_2}{28.02gN_2})(\frac{2molLi_3N}{1molN_2})(\frac{34.83gLi_3N}{1molLi_3N})$

= $86.8gLi_3N$

From above calculations, Li gives least amount of the product. So, 21.4 g of $Li_3N$ are formed.