Textbook M5

[DominicMalilay 1F]

Solve this exercise without using a calculator. The reaction 6 ClO 2 (g) + 2 BrF 3 (l) → 6 ClO 2 F (s) + Br 2 (l) is carried out with 12 mol ClO 2 and 5 mol BrF 3 . (a) Identify the excess reactant. (b) Estimate how many moles of each product will be produced and how many moles of the excess reactant will remain.

I calculated that the excess reactant is BrF since there is 4 mol needed while CLO2 needs 15 mol. However, I do not understand how to estimate how many moles of each product will be produced because if there are 15 moles needed for the reaction of CLO2, how can a reaction occur if we are only given 12 mol CLO2?

[Anh Trinh 1J]

a) You are right that is the excess reactant.

b) To calculate how many moles of each product will be produced, you have to find how many moles of each reactants are required for each time it is reacted. In the chemical reaction, 6 moles of and 1 mole of are produced from 6 moles and 2 moles . Because is the limiting reactant, we will use this to find how many moles of each product will be produced. We have 12 mol , and there is 6 required to produce 1 , then 2 mol is produced. 6 mole is required to produce 6 , and since we have 12 mol , 12 mol will be produced.

To find how many moles of the excess reactant () will remain, we have to note that 2 mol are used for every 6 mol , and because we have 12 mol (the limiting reactant), 4 mol () are required. We were given 5 mol () and only used 4, so there is 1 mol () remaining.

[Sedge Greenlee]

Hey! Anh Trinh gave a great explanation for this exact problem. For a more general explanation for solving limiting reaction problems, keep in mind that the chemical formula in terms of moles can be thought of as a ratio. For example, in this problem, for even 6 moles of ClO2, we produce 1 mole of Br2 and 6 moles of ClO2F. with this relationship established between the limiting reactant and the products, we can calculate how many moles of product are produced in relation to how many moles of the limiting reactant is provided. 2 sets of 6 moles of ClO2 produce 2 sets of 1 mole of Br2 and 2 sets of 6 moles of ClO2F, AKA 2 moles of Br2 and 12 moles of ClO2F.