Problem 22 - Chemistry The Molecular Science

Question

Balance these equations. (a) Reaction to produce hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4}:$$$ \mathrm{H}_{2} \mathrm{NCl}(\mathrm{aq})+\mathrm{NH}_{3}(\mathrm{~g}) \longrightarrow \mathrm{NH}_{4}\mathrm{Cl}(\mathrm{aq})+\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})$$ (b) Reaction of the fuels (dimethylhydrazine and dinitrogen tetraoxide) used in the Space Shuttle: \)\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~N}_{2} \mathrm{H}_{2}(\ell)+\mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g}) \longrightarrow\( $$\mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{~g})$$ (c) Reaction of calcium carbide with water to produce acetylene, \)\mathrm{C}_{2} \mathrm{H}_{2}$ $$\mathrm{CaC}_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2(\mathrm{~s})+\mathrm{C}_{2} \mathrm{H}_{2}(\mathrm{~g})$$

Step-by-Step Solution

Answer

(a) Multiply \(\mathrm{H}_{2}\mathrm{NCl}\) and \(\mathrm{NH}_{3}\) by 2.\n(b) Multiply \((\mathrm{CH}_{3})_{2}\mathrm{N}_{2}\mathrm{H}_{2}\) by 2 and \(\mathrm{N}_{2}\mathrm{O}_{4}\) by 3.\n(c) Multiply \(\mathrm{H}_{2}\mathrm{O}\) by 2.

Step 1: Identify the Reactants and Products

For each reaction, list the reactants and products clearly so you know exactly what substances you will be balancing.(a) Reactants: \( \mathrm{H}_{2}\mathrm{NCl} \), \( \mathrm{NH}_{3} \)Products: \( \mathrm{NH}_{4}\mathrm{Cl} \), \( \mathrm{N}_{2}\mathrm{H}_{4} \)(b) Reactants: \( (\mathrm{CH}_{3})_{2} \mathrm{N}_{2}\mathrm{H}_{2}, \mathrm{N}_{2}\mathrm{O}_{4} \)Products: \( \mathrm{N}_{2}, \mathrm{H}_{2}\mathrm{O}, \mathrm{CO}_{2} \)(c) Reactants: \( \mathrm{CaC}_{2}, \mathrm{H}_{2}\mathrm{O} \)Products: \( \mathrm{Ca(OH)}_{2}, \mathrm{C}_{2}\mathrm{H}_{2} \)

Step 2: Write Unbalanced Chemical Equations

Express each of the reactions in chemical equations without balancing the number of atoms.(a) \( \mathrm{H}_{2}\mathrm{NCl} + \mathrm{NH}_{3} \rightarrow \mathrm{NH}_{4}\mathrm{Cl} + \mathrm{N}_{2}\mathrm{H}_{4} \)(b) \( (\mathrm{CH}_{3})_{2} \mathrm{N}_{2}\mathrm{H}_{2} + \mathrm{N}_{2}\mathrm{O}_{4} \rightarrow \mathrm{N}_{2} + \mathrm{H}_{2}\mathrm{O} + \mathrm{CO}_{2} \)(c) \( \mathrm{CaC}_{2} + \mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{Ca(OH)}_{2} + \mathrm{C}_{2}\mathrm{H}_{2} \)

Step 3: Balance Each Reaction

Balance each reaction by adjusting coefficients to have the same number of each type of atom on both sides of the equation.(a)- Start with \( \mathrm{NCl} \) from \( \mathrm{H}_{2}\mathrm{NCl} \) and \( \mathrm{NH}_{4} \mathrm{Cl} \), hydrogen atoms, and \( \mathrm{N}_{2} \).- Balanced equation: \( 2\mathrm{H}_{2}\mathrm{NCl} + 2\mathrm{NH}_{3} \rightarrow 2\mathrm{NH}_{4}\mathrm{Cl} + \mathrm{N}_{2}\mathrm{H}_{4} \)(b)- Balance carbon atoms first.- Then, balance nitrogen, and then hydrogen and oxygen last.- Balanced equation: \( 2(\mathrm{CH}_{3})_{2}\mathrm{N}_{2}\mathrm{H}_{2} + 3\mathrm{N}_{2}\mathrm{O}_{4} \rightarrow 7\mathrm{N}_{2} + 8\mathrm{H}_{2}\mathrm{O} + 4\mathrm{CO}_{2} \)(c)- Balance calcium and hydrogen atoms first.- Then, balance carbon atoms.- Balanced equation: \( \mathrm{CaC}_{2} + 2\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{Ca(OH)}_{2} + \mathrm{C}_{2}\mathrm{H}_{2} \)

Key Concepts

Chemical Reactions

A chemical reaction occurs when substances, known as reactants, transform into new substances, called products. This transformation involves breaking old bonds and forming new ones. In the process of chemical reactions, there is a rearrangement of atoms, which enables the creation of products with new properties.
Chemical reactions can be classified into several types, including:

• Combination Reactions: Two or more substances combine to form a single product.
• Decomposition Reactions: A single substance breaks down into two or more products.
• Displacement Reactions: An element in a compound is displaced by another element.
• Redox Reactions: Involves the transfer of electrons between two species.
• Combustion Reactions: Involves oxygen reacting with a compound to produce heat and light.

Understanding the type of reaction helps in predicting the products and the conditions required for the reaction to occur. In the exercises, three types of reactions are provided, each with its unique reactants and products ready to be balanced.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships among the substances involved in a chemical reaction. It derives its principles from the laws of conservation of mass and energy.
Using stoichiometry, we can determine:

• The amount of each reactant needed to produce a desired amount of product.
• The amount of product that can be produced from given reactants.
• The ratios of reactant one to reactant two required to fully react.

Stoichiometry relies heavily on a balanced chemical equation, as it ensures that the number of atoms for each element are the same on both sides of the equation, thus conserving mass. This balance helps chemists calculate the precise amounts of substances required and predict how much product will be formed, making stoichiometry a vital tool in chemistry.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show how reactants are transformed into products through the use of symbols and formulas. Writing and balancing chemical equations are fundamental skills in chemistry that ensure the law of conservation of mass is followed.
A chemical equation consists of:

• Reactants: The starting substances, written on the left side.
• Products: The new substances formed, listed on the right side.
• Coefficients: Numbers placed before the formulas to indicate the quantity of each substance.
• Arrows: Used to show the direction of the reaction.

Balancing chemical equations involves adjusting the coefficients to ensure the same number of each type of atom exists on both sides of the equation. Through this process, you make sure the equation honors the conservation of atoms and mass. Balancing chemical equations is integral for solving stoichiometry problems as it allows calculations to be made accurately regarding quantities of reactants and products involved.