the balanced equation for the above reaction is as follows;
2K + Br₂ --> 2KBr
Stoichiometry of Br₂ to KBr is 1:2
we have been told that K is present which means that Br₂ is the limiting reactant. Limiting reactant is the reactant that is fully consumed in the reaction and amount of product formed depends on amount of limiting reactant present.
Number of Br moles reacted - 21.4 g / 160 g/mol = 0.134 mol
According to stoichiometry,
1 mol of Br₂ forms 2 mol of KBr
therefore 0.134 mol of Br₂ forms 2x0.134 = 0.268 mol of KBr
mass of KBr formed - 0.268 mol x 119 g/mol = 31.9 g of KBr
a mass of 31.9 g of KBr is formed
