Problem 18 - Chemistry The Central Science In Si Units

Question

Complete and balance the following equations: (a) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}(I)+\mathrm{O}_{2}(g) \longrightarrow\) (c) \(\mathrm{MnO}_{2}(s)+\mathrm{C}(s) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{AlP}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (e) \(\mathrm{Na}_{2} \mathrm{~S}(s)+\mathrm{HCl}(a q) \longrightarrow\)

Step-by-Step Solution

Answer

(a) Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3. (b) 2C3H7OH + 9O2 → 6CO2 + 8H2O. (c) MnO2 + C → Mn + CO2. (d) AlP + 3H2O → Al(OH)3 + PH3. (e) Na2S + 2HCl → 2NaCl + H2S.

Step 1: Understanding the Reaction

Examine each reactant and identify the possible products they might form when they react. For each of these reactions, use knowledge of chemistry to predict the products.

Step 2: Writing the Chemical Equations

For each reaction, write the possible products. (a) Mg3N2 reacts with water to form Mg(OH)2 and NH3. (b) The combustion of C3H7OH with oxygen forms CO2 and H2O. (c) MnO2 reacts with carbon to produce Mn and CO. (d) AlP reacts with water to form Al(OH)3 and PH3. (e) Na2S reacts with HCl to form NaCl and H2S.

Step 3: Balancing Equation (a)

The unbalanced equation is: \[ \mathrm{Mg}_{3} \mathrm{~N}_{2} + \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Mg(OH)}_2 + \mathrm{NH}_3 \] Balance the magnesium, nitrogen, oxygen, and hydrogen by writing: \[ \mathrm{Mg}_{3} \mathrm{~N}_{2} + 6\mathrm{H}_{2} \mathrm{O} \longrightarrow 3\mathrm{Mg(OH)}_2 + 2\mathrm{NH}_3 \]

Step 4: Balancing Equation (b)

The unbalanced equation is: \[ \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} + \mathrm{O}_{2} \longrightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O} \] Balance the carbon, hydrogen, and oxygen by writing: \[ 2\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} + 9\mathrm{O}_{2} \longrightarrow 6\mathrm{CO}_2 + 8\mathrm{H}_2\mathrm{O} \]

Step 5: Balancing Equation (c)

The unbalanced equation is: \[ \mathrm{MnO}_{2} + \mathrm{C} \longrightarrow \mathrm{Mn} + \mathrm{CO} \] Balance the manganese and oxygen by writing: \[ \mathrm{MnO}_{2} + \mathrm{C} \longrightarrow \mathrm{Mn} + \mathrm{CO}_2 \] No further balancing needed since we have equal Mn and O atoms on both sides.

Step 6: Balancing Equation (d)

The unbalanced equation is: \[ \mathrm{AlP} + \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Al(OH)}_3 + \mathrm{PH}_3 \] Balance the aluminum, phosphorus, oxygen, and hydrogen: \[ \mathrm{AlP} + 3\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Al(OH)}_3 + \mathrm{PH}_3 \]

Step 7: Balancing Equation (e)

The unbalanced equation is: \[ \mathrm{Na}_{2} \mathrm{~S} + \mathrm{HCl} \longrightarrow \mathrm{NaCl} + \mathrm{H}_{2} \mathrm{S} \] Balance the elements by writing: \[ \mathrm{Na}_{2} \mathrm{~S} + 2\mathrm{HCl} \longrightarrow 2\mathrm{NaCl} + \mathrm{H}_{2} \mathrm{S} \]

Key Concepts

Reaction Prediction

One of the first and essential steps in solving chemical equations is predicting the reaction products. This involves understanding the nature of the reactants to determine what they'll form. For example, when magnesium nitride (\(\mathrm{Mg}_{3} \mathrm{~N}_{2}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)), the products are typically magnesium hydroxide (\(\mathrm{Mg(OH)}_2\)) and ammonia (\(\mathrm{NH}_3\)). This prediction is based on the knowledge of chemistry, specifically recognizing that magnesium nitride breaks down in water to release ammonia and form hydroxides.
Reaction prediction requires deep familiarity with chemical properties and reaction types, such as synthesis, decomposition, and double displacement. It is a skill that develops over time with practice. To predict correctly:

• Understand the chemical nature of reactants.
• Be familiar with classic reaction patterns and expected products.
• Use the general principles of balancing charge and mass.

Chemical Equations

Once you predict the products of a reaction, the next step is to represent the reaction using a chemical equation. Chemical equations succinctly convey how reactants are transformed into products. For instance, the combustion of propanol (\(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\)) with oxygen (\(\mathrm{O}_{2}\)) can be written as: \[ \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} + \mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O} \]Chemical equations have specific characteristics:

• The left side shows the reactants, and the right side shows the products.
• Chemical symbols and formulas are used to describe substances.
• Using arrow (\(\rightarrow\)) indicates the direction from reactants to products.

Writing chemical equations helps in visualizing the reaction progress, understanding reactant consumption, and product formation.

Chemical Reactions

A chemical reaction is a transformation that converts substances, called reactants, into different substances, known as products. This involves making and breaking chemical bonds. For example, when aluminum phosphide (\(\mathrm{AlP}\)) reacts with water (\(\mathrm{H}_{2} \mathrm{O}\)), a chemical reaction takes place to form aluminum hydroxide (\(\mathrm{Al(OH)}_3\)) and phosphine (\(\mathrm{PH}_3\)).
Chemical reactions can be classified into different categories, including:

• Synthesis: Multiple reactants form a single product.
• Decomposition: A single reactant breaks down into multiple products.
• Single/Double displacement: Ions are exchanged between reactants to form products.

Each type of reaction follows specific patterns and principles, which help in predicting the products and balancing the equations.

Stoichiometry

Stoichiometry is the mathematical relationship between the quantities of reactants and products in a chemical reaction. It is essential for balancing chemical equations. For instance, in the reaction of sodium sulfide (\(\mathrm{Na}_{2} \mathrm{~S}\)) with hydrochloric acid (\(\mathrm{HCl}\)), stoichiometry helps us determine the exact mole ratio needed to produce sodium chloride (\(\mathrm{NaCl}\)) and hydrogen sulfide (\(\mathrm{H}_{2} \mathrm{S}\)).
Here are steps and tips for applying stoichiometry effectively:

• Start by writing the unbalanced chemical equation.
• Identify the chemical formulas of reactants and products.
• Use coefficients in front of chemical formulas to balance the equation, ensuring that the number of atoms for each element is equal on both sides of the equation.

By mastering stoichiometry, you will be able to: calculate exact quantities of needed reactants, predict product amounts, and ensure complete reactions. It is a fundamental concept that enhances the ability to predict yields and optimize reactions.