Ammonia can be formed by a direct reaction of nitrogen and hydrogen. N2(g) + 3 H2(g) 2 NH3(g) A tiny portion of the starting mixture is represented by the diagram, where the blue circles represent N and the white circles represent H. Which of these represents the product mixture? For the reaction of the given sample, which of these statements is true? (a) N2 is the limiting reactant. (b) H2 is the limiting reactant. (c) NH, is the limiting reactant. (d) No reactant is limiting: they are present in the correct stoichiometric ratio.

A common demonstration in chemistry courses involves adding a tiny speck of manganese(IV) oxide to a concentrated hydrogen peroxide (H2O2) solution. Hydrogen peroxide decomposes quite spectacularly under these conditions to produce oxygen gas and steam (water vapor). Manganese(IV) oxide is a catalyst for the decomposition of hydrogen peroxide and is not consumed in the reaction. Write the balanced equation for the decomposition reaction of hydrogen peroxide.

Acetone, (CH3)2CO, is an important industrial compound. Although its toxicity is relatively low, workers using it must be careful to avoid flames and sparks because this compound burns readily in air. Write the balanced equation for the combustion of acetone.

Explain how an equation can be balanced even if the number of reactant particles differs from the number of product particles.

What is meant by a limiting reactant in a particular reaction? In what way is the reaction “limited”? What does it mean to say that one or more of the reactants are present in excess? What happens to a reaction when the limiting reactant is used up?

3.75 The following pictures show a molecular-scale view of a chemical reaction between the compounds AB2 and B2. (A atoms are shown in blue and B atoms in white). The box on the left represents the reactants at the instant of mixing, and the box on the right shows what is left once the reac- tion has gone to completion. Write a balanced chemical equation for this reaction. As usual, your equation should use the smallest possible whole number coefficients for all substances.

4.106 An ore sample with a mass of 670 kg contains 27.7% magnesium carbonate, MgCO3. If all of the magnesium carbonate in this ore sample is decomposed to form carbon dioxide, describe how to determine what mass of CO2 is evolved during the process.

4.68 The pictures below show a molecular-scale view of a chemical reaction between the compounds AB2 and B2. (Green balls represent B atoms and orange balls are A atoms). The box on the left represents the reactants at the instant of mixing, and the box on the right shows what is left once the reaction has gone to completion. Was there a limiting reactant in this reaction? If so, what was it? Write a balanced chemical equation for this reaction. As usual, your equation should use the smallest possible whole number coefficients for all substances.

3.84 The picture shown depicts the species present at the start of a combustion reaction between methane, CH4, and oxygen, O2. (a) Draw the resulting state after this set of re- actants has reacted as far as possible. (b) Use the drawings to explain the stoichiometry represented in the balanced chemical equation for the combustion of methane.