Problem 5 - Chemistry and Chemical Reactivity

Question

Select one of the alkali metals, and write a balanced chemical equation for its reaction with chlorine. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Step-by-Step Solution

Answer

The balanced reaction is \( 2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl} \). The reaction is exothermic and produces an ionic compound.

Step 1: Selecting an Alkali Metal

Alkali metals are found in Group 1 of the periodic table. We'll select sodium (Na) as our example alkali metal.

Step 2: Writing the Chemical Equation

When sodium reacts with chlorine gas (Cl₂), it forms sodium chloride (NaCl). The unbalanced chemical equation is: \[ \text{Na} + \text{Cl}_2 \rightarrow \text{NaCl} \]

Step 3: Balancing the Chemical Equation

To balance the equation, note that one Cl₂ molecule provides two chlorine atoms, so you'll need two Na atoms to react with it. The balanced chemical equation is: \[ 2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl} \]

Step 4: Determining the Reaction Type

The reaction of an alkali metal like sodium with chlorine is highly exothermic. This is because a large amount of energy is released when the ionic bond is formed between Na⁺ and Cl⁻ ions.

Step 5: Identifying the Product Type

Sodium chloride (NaCl), the product of the reaction, is an ionic compound. This is due to the transfer of one electron from sodium to chlorine, resulting in a positive sodium ion and a negative chloride ion, which attract each other.

Key Concepts

Balancing Chemical Equations

Balancing chemical equations refers to ensuring that a chemical equation adheres to the principle of conservation of mass. This means that the number of each type of atom on the reactant side must be equal to the number of each type on the product side. For instance, in the reaction between sodium (Na) and chlorine gas (Cl₂), we initially wrote the unbalanced equation: \[ \text{Na} + \text{Cl}_2 \rightarrow \text{NaCl} \]To balance it, we observed that we need two sodium atoms for every chlorine molecule, as each Cl₂ molecule supplies two chlorine atoms. Therefore, the balanced equation becomes:\[ 2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl} \] Balancing equations is crucial because it ensures that the reaction obeys the law of conservation of mass, making predictions about quantities in a reaction more reliable.

Exothermic Reactions

In chemistry, exothermic reactions are those that release energy, usually in the form of heat, to their surroundings. This occurs because the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products. In the case of sodium reacting with chlorine: - A large amount of energy is released when the strong ionic bonds form between Na⁺ and Cl⁻ ions. - This reaction is therefore considered highly exothermic. You might notice heat, light, or even flames when such a reaction takes place—evidence of the energy being released into the environment. Exothermic reactions are common and include everyday processes like combustion, respiration, and many oxidation reactions.

Ionic Compounds

Ionic compounds are substances made up of ions, which are atoms or molecules with a net charge. This occurs when one atom transfers electrons to another atom, resulting in a compound composed of positively and negatively charged ions. In the reaction of sodium (Na) with chlorine (Cl): - Sodium atoms lose an electron to form Na⁺ ions. - Chlorine atoms gain an electron to form Cl⁻ ions. - The attraction between these oppositely charged ions results in the formation of sodium chloride (NaCl). These compounds exhibit the following characteristics:

• They typically form crystalline solids with high melting and boiling points.
• They can conduct electricity when dissolved in water, as the ions are free to move.
• The resulting materials often have a characteristic lattice structure.

Ionic compounds like sodium chloride are crucial in everyday life, from table salt in our diet to the function of nerves in the human body.