Problem 17 - Chemistry: The Central Science

Question

Complete and balance the following equations: (a) \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\mathrm{CuO}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow\) (c) \(\mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow\) (c) \(\mathrm{Al}_{1} \mathrm{C}_{1}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\)

Step-by-Step Solution

Answer

The balanced equations are: (a) \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{NaOH}(s)\) (b) \(\mathrm{CuO}(s)+ 2\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{Cu(NO}_{3})_{2}(a q) + \mathrm{H}_{2}\mathrm{O}(l)\) (c) \(\mathrm{WO}_{3}(s) + 3\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s) + 3\mathrm{H}_{2}\mathrm{O}(g)\) (d) \(2\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow 2\mathrm{H}_{2}\mathrm{O}(l) + \mathrm{N}_{2}(g)\) (e) \(\mathrm{AlC}(s) + 4\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al(OH)}_{3}(s) + 3\mathrm{CH}_{4}(g)\)

Step 1: (a) Balance the equation with NaOCH3 and H2O

: First, let's add water as a product: \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{2}\mathrm{O}(l)\) Now, balance each element in the equation. Add 1 molecule of NaOH as a product: \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{NaOH}(s)\) This equation is already balanced, with each element having the same number of atoms on both sides.

Step 2: (b) Balance the equation with CuO and HNO3

: First, add the products for this equation: Cu(NO3)2 + H2O \(\mathrm{CuO}(s)+\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{Cu(NO}_{3})_{2}(a q) + \mathrm{H}_{2}\mathrm{O}(l)\) To balance this equation, add a 2 in front of HNO3: \(\mathrm{CuO}(s)+ 2\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{Cu(NO}_{3})_{2}(a q) + \mathrm{H}_{2}\mathrm{O}(l)\) This equation is now balanced.

Step 3: (c) Balance the equation with WO3 and H2

: First, add the product for this equation: W + H2O \(\mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s) + \mathrm{H}_{2}\mathrm{O}(g)\) To balance this equation, add a 3 in front of H2 and a 3 in front of H2O: \(\mathrm{WO}_{3}(s) + 3\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s) + 3\mathrm{H}_{2}\mathrm{O}(g)\) This equation is now balanced.

Step 4: (d) Balance the equation with NH2OH and O2

: First, add the products for this equation: H2O + N2 \(\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{N}_{2}(g)\) To balance this equation, add a 2 in front of NH2OH, a 2 in front of H2O, and a 1 in front of O2: \(2\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow 2\mathrm{H}_{2}\mathrm{O}(l) + \mathrm{N}_{2}(g)\) This equation is now balanced.

Step 5: (e) Balance the equation with AlC and H2O

: First, add the products for this equation: Al(OH)3 + CH4 \(\mathrm{AlC}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al(OH)}_{3}(s) + \mathrm{CH}_{4}(g)\) To balance this equation, add a 4 in front of H2O and a 3 in front of CH4: \(\mathrm{AlC}(s) + 4\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al(OH)}_{3}(s) + 3\mathrm{CH}_{4}(g)\) This equation is now balanced.

Key Concepts

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It is based on the conservation of mass where the total mass of reactants equals the total mass of products. Thus, stoichiometry involves the calculation of the amounts of substances involved in chemical reactions.

For a chemical equation to be stoichiometrically balanced, each element must have the same number of atoms on both sides of the reaction. This is critical for solving problems related to chemical quantities in reactions, such as determining the mass of a reactant needed to produce a certain amount of product. Understanding stoichiometry is also essential for predicting the yield of a reaction, and for scaling laboratory reactions to industrial production.

When working to improve stoichiometric calculations, it's important to focus on identifying the limiting reactants, determining the theoretical yield, and calculating percent yields. Avoiding common errors in balancing equations, such as miscounting atoms or overlooking the states of matter for each compound, is also crucial for accurate stoichiometry.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds to create new substances. To understand chemical reactions, one must look at the reactants, which are the starting substances, and the products, which are the substances formed as a result of the reaction.

Chemical equations represent these reactions, with reactants on the left side of the arrow and products on the right. The arrow symbolizes the direction of the reaction. Reactions may be categorized into various types, such as synthesis, decomposition, single-displacement, and double-displacement reactions. Balancing these equations is imperative because it reflects the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a closed system.

To improve understanding of chemical reactions, delve into reaction mechanisms, which describe the step-by-step process by which a reaction occurs. Understanding energy changes, such as endothermic and exothermic reactions, and reaction rates also provides a deeper insight into how and why certain reactions happen.

Chemical Formulas

Chemical formulas provide a way to represent chemical substances using symbols for the elements and numbers to indicate the proportions of each element present in the substance. A correctly written formula is foundational for balancing chemical equations because it communicates the exact composition of a compound. There are different types of chemical formulas: empirical formulas show the simplest integer ratio of elements in a compound, molecular formulas show the actual number of atoms of each element in a molecule, and structural formulas depict how atoms are arranged.

To enhance comprehension of chemical formulas, focus on learning to interpret and write them correctly, including understanding the significance of subscripts and parentheses. Being able to deduce the molecular formula from an empirical formula by using the molecular weight is a key skill that can be developed with practice. Additionally, recognizing common polyatomic ions and their corresponding charges can significantly aid in writing correct chemical formulas for ionic compounds.