Question

Complete and balance each gas evolution reaction. (a) \(\mathrm{HClO}_{4}(a q)+\mathrm{K}_{2} \mathrm{CO}_{3}(a q) \longrightarrow\) (b) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{LiHSO}_{3}(a q)\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \longrightarrow\) (d) \(\mathrm{HCl}(a q)+\mathrm{ZnS}(s) \longrightarrow\)

Short answer

The balanced reactions are: (a) \( 2HClO_{4}(aq) + K_{2}CO_{3}(aq) \rightarrow 2KClO_{4}(aq) + CO_{2}(g) + H_{2}O(l) \), (b) \( HC_{2}H_{3}O_{2}(aq) + LiHSO_{3}(aq) \rightarrow LiC_{2}H_{3}O_{2}(aq) + SO_{2}(g) + H_{2}O(l) \), (c) \( (NH_{4})_{2}SO_{4}(aq) + Ca(OH)_{2}(aq) \rightarrow CaSO_{4}(s) + 2NH_{3}(g) + 2H_{2}O(l) \), (d) \( 2HCl(aq) + ZnS(s) \rightarrow ZnCl_{2}(aq) + H_{2}S(g) \).

Step-by-step solution

Identify the Reactions

Identify the types of reactions and the products that will evolve as gases. For reactions involving acids and carbonates, the gas evolved will be CO2. For reactions involving sulfites and acids, the gas evolved will be SO2. For reactions involving ammonium salts and hydroxides, the gas evolved will be NH3. For reactions with hydrochloric acid and a sulfide, the gas evolved will be H2S.

Balance Reaction (a)

For reaction (a), HClO4 reacts with K2CO3 to produce KClO4, CO2, and H2O. The balanced equation is: \[ 2HClO_4(aq) + K_2CO_3(aq) \rightarrow 2KClO_4(aq) + CO_2(g) + H_2O(l) \]

Balance Reaction (b)

For reaction (b), HC2H3O2 (acetic acid) reacts with LiHSO3 to produce LiC2H3O2, SO2, and H2O. The balanced equation is: \[ HC_2H_3O_2(aq) + LiHSO_3(aq) \rightarrow LiC_2H_3O_2(aq) + SO_2(g) + H_2O(l) \]

Balance Reaction (c)

For reaction (c), (NH4)2SO4 reacts with Ca(OH)2 to produce CaSO4, NH3, and H2O. The balanced equation is: \[ (NH_4)_2SO_4(aq) + Ca(OH)_2(aq) \rightarrow CaSO_4(s) + 2NH_3(g) + 2H_2O(l) \]

Balance Reaction (d)

For reaction (d), HCl reacts with ZnS to produce ZnCl2 and H2S. The balanced equation is: \[ 2HCl(aq) + ZnS(s) \rightarrow ZnCl_2(aq) + H_2S(g) \]

Key concepts

Balancing Chemical Equations

When chemists conduct reactions, it's crucial to make sure that they have the correct amounts of each reactant so that the reaction can proceed efficiently. This practice is known as balancing chemical equations. An unbalanced chemical equation shows the reactants and products, but doesn't reflect the conservation of mass. To balance a chemical equation, we adjust the coefficients (the numbers before the chemical formulas) so that the same number of each type of atom appears on both sides of the equation. It's a bit like a seesaw; both sides need to be equally 'weighted' for it to be balanced.

For example, in the reaction where hydrochloric acid reacts with potassium carbonate, balancing the equation ensures that the number of hydrogen, chlorine, potassium, carbon, and oxygen atoms in the reactants matches the number in the products. It's important to change only the coefficients and not the subscripts in the chemical formulas as changing the subscripts would create different chemicals entirely. Balancing chemical equations is a foundational skill in chemistry because it allows us to predict the amounts of each substance that will be used or produced in a chemical reaction.

Reaction Types

Understanding the types of chemical reactions helps chemists to predict the products that will form when different substances are combined. There are several categories of reactions, including synthesis, decomposition, single replacement, double replacement, combustion, and gas evolution reactions. Gas evolution reactions are a subset of double replacement reactions where the products include a gas, a liquid, and often a precipitate.

In the exercises provided, reaction (a) is a typical example of an acid reacting with a carbonate to produce a salt, carbon dioxide, and water. Reaction (b) involves an acid reacting with a sulfite, yielding a salt, sulfur dioxide, and water. Reaction (c) shows an ammonium salt reacting with a hydroxide, resulting in a salt, ammonia, and water. Lastly, reaction (d) is a single replacement reaction where an acid reacts with a sulfide, giving a salt and hydrogen sulfide gas. Knowing the types of reactions and the typical products that form allows us to write and balance the chemical equations correctly.

Stoichiometry

Stoichiometry is like the recipe for a chemical reaction. It tells you how much of each reactant you will need and how much of each product you will make. When we balance chemical equations, we get the stoichiometric coefficients that provide the proportions of reactants and products. For example, in a balanced equation \( 2HCl + ZnS \rightarrow ZnCl_2 + H_2S \), the coefficients tell us that 2 moles of hydrochloric acid react with 1 mole of zinc sulfide to produce 1 mole of zinc chloride and 1 mole of hydrogen sulfide gas.

Real-World Applications

Stoichiometry isn't just a concept for the classroom; it's essential in many real-world applications. Pharmaceutical companies use stoichiometry to determine how much of a drug's active ingredient is needed to produce the desired effect. Engineers use stoichiometry to predict how much fuel is required to launch a rocket. In environmental science, stoichiometry is used to understand how pollutants react in the atmosphere. It is a critical tool in the chemist's toolkit, enabling precise measurements and predictions in chemical reactions.