stoichometry question

Question

Zinc sulfide solid reacts with oxygen gas to produce solid zinc oxide and sulfur dioxide gas. A mixture of the reactants originally contains 380.0 g of zinc sulfide and 176.0 g of oxygen gas. What is the limiting reactant? How much of the excess reactant (in grams) remains?

Write a balanced chemical equation for each of the following. (Do not forget to include the states of matter.)

Aqueous cobalt(III) nitrate reacts with aqueous ammonium sulfide to produce solid cobalt(III) sulfide and aqueous ammonium nitrate.

Gaseous dinitrogen pentoxide decomposes into gaseous nitrogen dioxide and oxygen gas.

Answer 1

the oxidation of zinc sulfide produces the products zinc oxide and sulfur dioxide, thus the equation below

ZnS + O₂ → ZnO + SO₂

Since zinc and sulfur are balanced multiply the coefficients of compounds containing these elements by 2 and proceed to balance oxygen

2ZnS + 3O₂ → 2ZnO + 2SO₂

From the balanced equation we see that 3 moles of oxygen gas are needed to oxidize 2 moles of zinc sulfide completely.

Molar mass of zinc sulfide = 65.4 + 32.1 = 97.5

Moles of zinc sulfide = 380/97.5 = 3.90

Molar mass of O₂ = 2(16) = 32

Number of moles of oxygen gas = 176/32 = 5.5

Number of moles of oxygen gas needed to oxidize 3.90 moles of zinc sulfide = 3(3.90)/2 = 5.85 > 5.5

so oxygen is the limiting reagent.

5.5 moles of oxygen can oxidize 2(5.5)/3 = 11/3 moles of zinc sulfide.

Mass of zinc sulfide oxidized = (11/3)(97.5) = 357.5g

Thus 380.0g - 375.5g = 4.5g of zinc sulfide remains.

For the second reaction note the oxidation states of cobalt (+3), sulfide(-2) and ammonium (+1) ions.

Co(NO₃)_3(aq) + (NH₄)₂S _(aq)→ Co₂S_3(s) + NH₄NO_3(aq)

2Co(NO₃)_3(aq) + (NH₄)₂S_(aq) → Co₂S_3(s) + NH₄NO_3(aq) (balance cobalt)

2Co(NO₃)_3(aq) +3 (NH₄)₂S_(aq) → Co₂S_3(s) + NH₄NO_3(aq) (balance sulfur)

2Co(NO₃)_3(aq) + 3(NH₄)₂S_(aq) → Co₂S_3(s) + 6 NH₄NO_3(aq) (balance nitrogen and note hydrogen and oxygen are balanced)

The last equation is the decomposition of dinitrogen hydroxide to form nitrogen oxide and oxygen gas.

N₂O₅ → NO₂ + O₂

Balance nitrogen first then oxygen

N₂O₅ → 2NO₂ + O₂

2N₂O₅ → 4NO₂ + O₂