Write a balanced molecular equation describing each of the following chemical reactions. (a) Solid calcium carbonate is heated and decomposes to solid calcium oxide and carbon dioxide gas. (b) Gaseous butane, C4H10, reacts with diatomic oxygen gas to yield gaseous carbon dioxide and water vapor. (c) Aqueous solutions of magnesium chloride and sodium hydroxide react to produce solid magnesium hydroxide and aqueous sodium chloride. (d) Water vapor reacts with sodium metal to produce solid sodium hydroxide and hydrogen gas.

a. CaCO₃ (s) → CaO (s) + CO₂ (g) ΔH

b. 2C₄H₁₀ (g) + 13O₂ (g) → 8CO₂ (g) + 10H₂O (g)

c. MgCl₂ (aq) + 2NaOH (aq) → Mg (OH) ₂ (s) ↓ + 2NaCl (aq)

d. 2H₂O (g) + 2Na (s) → 2NaOH (s) + H₂ (g)

Explanation:

We identify the compound by the formula and we make the reaction with the phases of each reactant and product:

a. CaCO₃ (s); CaO (s), CO₂ (g)

The reaction is: CaCO₃ (s) → CaO (s) + CO₂ (g) ΔH

We add the ΔH symbol because there is heat added to the reaction, which means a enthalpy change

b. C₄H₁₀ (g), O₂ (g); CO₂ (g), H₂O (g)

The reaction is: 2C₄H₁₀ (g) + 13O₂ (g) → 8CO₂ (g) + 10H₂O (g)

In order to balance, we add 10 moles to water, so in total we have 20 H. Therefore we need 2 moles of butane to have 20 H, but we also have 8 C. So we need 8 C for the CO₂. By the end we have 16 O in CO₂ plus 10 O from water. In conclussion we need 13 O₂ in the reactant side to get the final balance

c. MgCl₂ (aq), NaOH (aq); Mg (OH) ₂ (aq), NaCl

The reaction is: MgCl₂ (aq) + 2NaOH (aq) → Mg (OH) ₂ (s) ↓ + 2NaCl (aq)

As the Mg (OH) ₂ is solid, it indicates that we made a precipitate in the reaction (That's why we add ↓, in the product side). We need 2NaCl, to balance the Cl and 2 NaOH to balance the Na.

Finally the Mg is balanced

d. H₂O (g), Na (s); NaOH (s), H₂ (g)

Reaction is: 2H₂O (g) + 2Na (s) → 2NaOH (s) + H₂ (g)

We add 2 water in order to balance the hydrogen gas, but we need a 2 in the hydoxide. Finally we will balance the Na with also a 2.