Question

Write the formula for the missing reactant or product in each of the following chemical equations. a. \(\mathrm{CH}_{4}(g)+\mathrm{Cl}_{2}(g) \rightarrow\) _________ \(+\mathrm{HCl}(g)\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}(g) \rightarrow \mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}(g)+\) _________ c. \(\mathrm{CHCl}_{3}(l)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CCl}_{4}(l)+\) __________

Short answer

The balanced chemical reactions with the missing reactants and products are: a. \(CH_{4}(g) + Cl_{2}(g) \rightarrow CH_{3}Cl(g) + HCl(g)\) b. \(CH_{3}CH_{2}CH_{3}(g) \rightarrow CH_{3}CH=CH_{2}(g) + H_{2}(g)\) c. \(2CHCl_{3}(l) + 2Cl_{2}(g) \rightarrow 2CCl_{4}(l) + H_{2}(g)\)

Step-by-step solution

Understand and Balance the First Reaction

In the first reaction, we have methane (\(CH_{4}\)) reacting with chlorine (\(Cl_{2}\)) to form hydrochloric acid (\(HCl\)) and an unknown product. To find the missing reactant or product, the number of atoms of each element on both sides of the reaction must be equal. Looking at the given side of the equation, there are 1 carbon atom, 4 hydrogen atoms and 2 chlorine atoms. In the products, there are 1 hydrogen atom and 1 chlorine atom in \(HCl\). The missing product should then contain 1 carbon atom, 3 hydrogen atoms and 1 chlorine atom to balance the equation. This compound is \(CH_{3}Cl\).

Understand and Balance the Second Reaction

In the second reaction, we have propane (\(CH_{3}CH_{2}CH_{3}\)) reacting to form propene (\(CH_{3}CH=CH_{2}\)) and an unknown product. On the reactant side, there are 3 carbon atoms, 8 hydrogen atoms. In the products, the propene molecule has 3 carbon atoms and 6 hydrogen atoms. The missing molecule must then contain 2 hydrogen atoms to make a total of 8 on both sides of the equation. So, the missing product is \(H_{2}\).

Understand and Balance the Third Reaction

In the third reaction, we have chloroform (\(CHCl_{3}\)) reacting with chlorine (\(Cl_{2}\)) to form carbon tetrachloride (\(CCl_{4}\)) and an unknown product. On the reactant side, there are 1 carbon atom, 1 hydrogen atom, and 5 chlorine atoms. In the products, \(CCl_{4}\) is providing 4 chlorine atoms. In order to balance the equation, a single hydrogen atom is needed. The simplest form of hydrogen provided by a molecule is hydrogen gas, \(H_{2}\). Here we should remember that hydrogen forms diatomic molecules, meaning it occurs in pairs in its gaseous, standard state. So the balanced reaction would involve 1/2 molecule of \(H_{2}\) which is actually just a single hydrogen atom. This can be removed by doubling the entire equation, but in its simplest form the missing reactant is \(H_{2}\). So the balanced reactions are: a. \(CH_{4}(g) + Cl_{2}(g) \rightarrow CH_{3}Cl(g) + HCl(g)\) b. \(CH_{3}CH_{2}CH_{3}(g) \rightarrow CH_{3}CH=CH_{2}(g) + H_{2}(g)\) c. \(CHCl_{3}(l) + Cl_{2}(g) \rightarrow CCl_{4}(l) + 0.5H_{2}(g)\) where 0.5 \(H_{2}\) represents a single hydrogen atom, or with the entire equation doubled for whole number stoichiometric coefficients: \(2CHCl_{3}(l) + 2Cl_{2}(g) \rightarrow 2CCl_{4}(l) + H_{2}(g)\)

Key concepts

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, are transformed into different substances, called products. During a chemical reaction, the atomic structure of the reactants changes, forming new bonds to create new substances.
This process is usually represented by a chemical equation, which shows the reactants on the left side and the products on the right, separated by an arrow indicating the direction of the transformation.

• Reactions can be simple, involving only a few atoms and bonds, or complex, including multiple steps and intermediate compounds.
• They can also be classified into categories such as synthesis, decomposition, single replacement, double replacement, and combustion.

Understanding these reactions is crucial in fields like organic chemistry, where the transformation of molecules is fundamental.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the substances involved in chemical reactions. It helps in determining the exact amounts of reactants needed to produce a desired quantity of product.
The stoichiometric coefficients in a balanced chemical equation indicate the molar ratios of the reactants and products involved in the reaction.

• This concept is vital for ensuring reactions proceed with maximum efficiency and that resources are not wasted.
• Accurate stoichiometric calculations allow chemists to scale reactions up or down, depending on the quantity of product required.

Understanding stoichiometry helps link the theoretical world of equations with the practical world of laboratory and industrial chemical processes.

Balancing Equations

Balancing chemical equations is an essential skill in chemistry. It ensures that the Law of Conservation of Mass is obeyed. This law states that mass cannot be created or destroyed in a chemical reaction.
The number of atoms of each element must be equal on both the reactant and product sides of the equation.

• To balance an equation, you might need to adjust the coefficients— the numbers in front of molecules— without changing the compound's chemical formula.
• Balancing ensures that chemical equations accurately represent what happens during a reaction and reflects the precise amounts of substances involved.

Practice is crucial, as it helps develop a systematic approach to balancing complex reactions, especially useful in organic chemistry.

Organic Chemistry

Organic chemistry focuses on the study of carbon-containing compounds. These compounds include not just hydrocarbons but also derivatives containing oxygen, nitrogen, sulfur, and other elements.
Organic chemistry is a vast discipline because carbon atoms can form stable bonds with many elements, leading to an immense variety of molecules.

• The study often involves understanding how molecules interact and react with each other, requiring a strong grasp of organic chemical reactions and mechanisms.
• It includes the synthesis, structure, reactivity, and properties of organic molecules.

Mastery in organic chemistry is crucial for fields such as pharmaceuticals, petrochemicals, food chemistry, and materials science.