What mass of bromine gas will form from the complete reaction of 150 g potassium bromide and 120 g of chlorine
This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants.
1. Write and balance the equation.
2. Convert 150 g KBr to mols. mols = grams/molar mass
3. Convert 120 g Cl2 to mols.
4a. Using the coefficients in the balanced equation, convert mols KBr to mols Br2.
4b. Do the same for Cl2 to Br2.
4c. It is unlikely that the two values from 4a and 4b will agree which means one of them is wrong. The correct value in LR problem is ALWAYS the smaller value and the reagent producing that value is the LR.
5. Now convert the smaller value to grams. g = mols x molar mass.
Post your work if you get stuck.