Question

Write complete, balanced equations for each of the following reactions. (a) When solid sodium hydride, \(\mathrm{NaH}\), is added to water, hydrogen gas is released and aqueous sodium hydroxide forms. (b) Aluminum metal reacts with chlorine gas to form solid aluminum chloride.

Short answer

The balanced chemical reactions are: (a) \(\mathrm{NaH + H_2O → NaOH + H_2}\) (b) \(\mathrm{2Al + 3Cl_2 → 2AlCl_3}\)

Step-by-step solution

- Identify the reactants and the products

In reaction (a), the reactants are solid sodium hydride (\(\mathrm{NaH}\)) and water. The products are hydrogen gas and aqueous sodium hydroxide. In reaction (b), the reactants are aluminum metal and chlorine gas and the product is solid aluminum chloride.

- Write down the unbalanced chemical equations

For reaction (a), the unbalanced chemical equation may be written as: \(\mathrm{NaH + H_2O → NaOH + H_2}\). For reaction (b), the unbalanced chemical equation is: \(\mathrm{Al + Cl_2 → AlCl_3}\).

- Balance the equations

For reaction (a), the equantion is already balanced. For reaction (b), to balance the equation, place a 2 in front of \(\mathrm{Al}\) and 3 in front of \(\mathrm{Cl_2}\) on the left-hand side. This leads to \(\mathrm{2Al + 3Cl_2 → 2AlCl_3}\).

Key concepts

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry. It involves ensuring that the number of each type of atom is the same on both sides of a chemical equation. This reflects the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction.

When balancing equations, follow these steps:

• Write down the unbalanced equation with the correct formulas for all reactants and products.
• Count the number of atoms of each element on both sides of the equation.
• Add coefficients in front of the chemical formulas to balance the number of atoms for each element. Never change the subscripts in chemical formulas.
• Verify that the equation is balanced by recounting the atoms for each element.

For example, in the reaction between aluminum and chlorine gas to form aluminum chloride, the balanced equation is \[2\mathrm{Al} + 3\mathrm{Cl}_2 \rightarrow 2\mathrm{AlCl}_3\] meaning there are the same numbers of aluminum and chlorine atoms on both sides.

Reactants and Products

Understanding reactants and products is crucial in studying chemical reactions. Reactants are the starting substances that undergo change, and products are the substances formed as a result of the reaction.

In any chemical reaction, such as the one involving sodium hydride and water, identify the substances reacting and those being produced. For sodium hydride reacting with water:

• Reactants: Solid sodium hydride (\(\mathrm{NaH}\)) and water (\(\mathrm{H_2O}\))
• Products: Hydrogen gas (\(\mathrm{H_2}\)) and aqueous sodium hydroxide (\(\mathrm{NaOH}\))

This distinction helps to understand what changes during the reaction and to successfully balance the chemical equation.

Sodium Hydride Reaction

The reaction of sodium hydride with water is an example of a chemical process that is common in both laboratory and industrial settings. When sodium hydride (\(\mathrm{NaH}\)) is added to water, it reacts vigorously to produce hydrogen gas (\(\mathrm{H_2}\)) and sodium hydroxide (\(\mathrm{NaOH}\)).

The balanced chemical equation for this reaction is as follows: \[\mathrm{NaH + H_2O \rightarrow NaOH + H_2}\]

This reaction is interesting because it demonstrates the reactivity of alkali metal hydrides, like sodium hydride, with water. The production of hydrogen gas is a key observation, often causing bubbling or fizzing. Such reactions are exothermic, releasing energy as heat, which can sometimes be vigorous enough to be noticeable. Understanding this reaction is important for safety, allowing chemists to handle such substances with care.