Zinc sulfide reacts with oxygen according to the reaction: 2 ZnS(s) + 3 O₂(g) → 2 ZnO(s) + 2 SO₂( g) A reaction mixture initially contains 4.2 mol ZnS and 6.8 mol O₂. Once the reaction has occurred as completely as possible, what amount (in moles) of the excess reactant remains?

Key Concepts

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the proportions of substances involved in a reaction, which is essential for identifying limiting and excess reactants. In this case, stoichiometry will help us find out how much of each reactant is consumed and how much remains after the reaction.

Limiting Reactant

The limiting reactant is the substance that is completely consumed first in a chemical reaction, thus determining the maximum amount of product that can be formed. Identifying the limiting reactant is crucial for calculating the amounts of excess reactants left over after the reaction. In this scenario, we need to determine which reactant, ZnS or O2, limits the reaction to find the excess.

Excess Reactant

An excess reactant is a reactant that remains after the reaction has gone to completion because it was not completely consumed. Understanding the concept of excess reactants is important for calculating how much of a particular reactant is left over after the reaction. In this problem, we will calculate the moles of the excess reactant remaining after the reaction between ZnS and O2.