Answer:
[tex]\large \boxed{\text{a) HBr; b) K; c) 0.0503 g}}[/tex]
Explanation:
The limiting reactant is the reactant that gives the smaller amount of product.
Assemble all the data in one place, with molar masses above the formulas and masses below them.
M_r: 39.10 80.41 2.016
2K + 2HBr ⟶ 2KBr + H₂
m/g: 5.5 4.04
a) Limiting reactant
(i) Calculate the moles of each reactant
[tex]\text{Moles of K} = \text{5.5 g} \times \dfrac{\text{1 mol}}{\text{31.10 g}} = \text{0.141 mol K}\\\\\text{Moles of HBr} = \text{4.04 g} \times \dfrac{\text{1 mol}}{\text{80.91 g}} = \text{0.049 93 mol HBr}[/tex]
(ii) Calculate the moles of H₂ we can obtain from each reactant.
From K:
The molar ratio of H₂:K is 1:2.
From HBr:
The molar ratio of H₂:HBr is 3:2.
[tex]\text{Moles of H}_{2} = \text{0.049 93 mol HBr } \times \dfrac{\text{1 mol H}_{2}}{\text{2 mol HBr}} = \text{0.024 97 mol H}_{2}[/tex]
(iii) Identify the limiting reactant
HBr is the limiting reactant because it gives the smaller amount of NH₃.
b) Excess reactant
The excess reactant is K.
c) Mass of H₂
[tex]\text{Mass of H}_{2} = \text{0.024 97 mol H}_{2} \times \dfrac{\text{2.016 g H}_{2}}{\text{1 mol H}_{2}} = \textbf{0.0503 g H}_{2}\\\text{The mass of hydrogen is $\large \boxed{\textbf{0.0503 g}}$}[/tex]
