Question

Complete and balance each gas-evolution equation. a. \(\mathrm{HBr}(a q)+\mathrm{NiS}(s) \longrightarrow\) b. \(\mathrm{NH}_{4} \mathrm{I}(a q)+\mathrm{NaOH}(a q) \longrightarrow\) c. \(\operatorname{HBr}(a q)+\mathrm{Na}_{2} \mathrm{~S}(a q) \longrightarrow\) d. \(\mathrm{HClO}_{4}(a q)+\mathrm{Li}_{2} \mathrm{CO}_{3}(a q) \longrightarrow\)

Short answer

a. HBr(aq) + NiS(s) \rightarrow H2S(g) + NiBr2(aq), b. NH4I(aq) + NaOH(aq) \rightarrow NH3(g) + H2O(l) + NaI(aq), c. 2HBr(aq) + Na2S(aq) \rightarrow H2S(g) + 2NaBr(aq), d. 2HClO4(aq) + Li2CO3(aq) \rightarrow 2LiClO4(aq) + H2O(l) + CO2(g)

Step-by-step solution

- Analyze and Write the Reactions for Each Equation

Identify the reactants in each equation and predict the possible products based on the types of reactions that typically occur between acids and sulfides, acids and carbonates, and between an ammonium salt and a strong base.

- Balance the Reactions for Hydrogen Sulfide Evolution

For reactions (a) and (c), where HBr reacts with a sulfide, hydrogen sulfide gas is likely to evolve. Write the balanced chemical equations by ensuring the conservation of mass, which requires that each element has the same number of atoms on both sides of the equation.

- Balance the Reaction for Ammonia Gas Evolution

For reaction (b), when an ammonium salt reacts with a strong base, ammonia gas will evolve. Balance this equation by adjusting coefficients to ensure that the number of each type of atom is the same on both sides.

- Balance the Reaction for Carbon Dioxide Evolution

For reaction (d), where an acid reacts with a carbonate, carbon dioxide gas will evolve. Write the balanced chemical equation by ensuring that atoms are conserved.

Key concepts

Chemical Reaction Balancing

Balancing chemical reactions is like solving a puzzle where the pieces are atoms, and you must make sure they fit perfectly on either side of the equation. This is crucial because of the Law of Conservation of Mass, which states that matter cannot be created or destroyed, only rearranged. To balance an equation, count the number of each type of atom on both sides. If they don't match, adjust the coefficients, which are the numbers in front of the chemical formulas, until they do.

Imagine if you have a seesaw and you want it to balance perfectly. Just as you would add or remove weights from each side, you adjust the coefficients in the chemical equation to balance the atoms. This process ensures that the equations reflect what actually happens in a chemical reaction and is essential for correctly predicting products and their amounts.

Acid-Base Reactions

Acid-base reactions are among the most common and fundamental reactions in chemistry where acids donate protons, and bases accept them. In an equation, when an acid and a base react, they often produce a salt and water, a process known as neutralization.

An easy way to recognize an acid is that many start with 'H,' indicating a hydrogen that can be given away, like \text{HCl} (hydrochloric acid) or \text{H}\(_2\)SO\(_4\) (sulfuric acid). Bases often contain OH groups, like \text{NaOH} (sodium hydroxide) or \text{KOH} (potassium hydroxide). When they react, the H from the acid joins the OH from the base, creating H\(_2\)O, or water, and the remaining parts form the salt. For example, HCl + NaOH \(\rightarrow\) NaCl + H\(_2\)O.

Gas Evolution from Reactions

Gas evolution in chemical reactions refers to the process where certain reactants combine and produce a gas as a product. This gas often bubbles out of the solution, which can serve as a visual cue that a reaction has occurred.

Common gases that evolve in such reactions include hydrogen sulfide (H\(_2\)S), ammonia (NH\(_3\)), and carbon dioxide (CO\(_2\)). For instance, in the given exercises, you can expect that when an acid such as HBr reacts with a sulfide like NiS, the characteristic rotten egg smell of hydrogen sulfide gas may be noted. Similarly, when a carbonate is mixed with an acid, watch out for the fizzing release of carbon dioxide gas, like when you open a carbonated drink. Understanding the types of reactants that lead to gas evolution can help you predict the products and write accurate chemical equations.

Stoichiometry

Stoichiometry in chemistry might remind you of following a cooking recipe. It's all about the ratios and proportions of ingredients—except, instead of cups and teaspoons, chemists use moles to measure the amount of substances in a reaction. With stoichiometry, we can calculate the amounts of reactants needed to produce a certain amount of product, or vice versa.

For example, in equation (b), if you know how much \text{NH}\(_4\)I you have, stoichiometry allows you to determine how much \text{NaOH} is required to react with it completely. More simply put, stoichiometry tells you how much of each substance you need to mix and what amount you'll get out. It involves using the balanced equation as a recipe to relate the quantities of reactants and products through mole ratios derived from the coefficients in the balanced equation.