3.49P - Chemistry: Molecular Nature Of Matter And Change

Question

Question. In the process of balancing the equation

$\mathbf{Al}\mathbf{+}{\mathbf{Cl}}_{\mathbf{2}}\mathbf{\to }{\mathbf{AlCl}}_{\mathbf{3}}$

Student I writes: $\mathbf{Al}\mathbf{+}{\mathbf{Cl}}_{\mathbf{2}}\mathbf{\to }{\mathbf{AlCl}}_{\mathbf{2}}$

Student II writes: $\mathbf{Al}\mathbf{+}{\mathbf{Cl}}_{\mathbf{2}}\mathbf{+}\mathbf{Cl}\mathbf{\to }{\mathbf{AlCl}}_{\mathbf{3}}$

Student III writes: $\mathbf{2}\mathbf{Al}\mathbf{+}\mathbf{3}{\mathbf{Cl}}_{\mathbf{2}}\mathbf{\to }\mathbf{2}{\mathbf{AlCl}}_{\mathbf{3}}$

Is the approach of Student I valid? Student II? Student III? Explain.

Step-by-Step Solution

Answer

Changing the subscripts is incorrect as it will alter the chemical formula. While balancing an equation can be done by adding a coefficient to the front of a chemical formula.

There is an equal number of moles on both sides.

$2\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to 2{\mathrm{AlCl}}_3\left(\mathrm{s}\right)$

Step1. Considering the following chemical equations:

$2\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to 2{\mathrm{AlCl}}_3\left(\mathrm{s}\right)$

Here Al and Cl₂ are reactants, AlCl₃ is the product and the arrow indicates the direction of the reaction proceed.

Whereas (s) indicates solid, (g) is gas. Also, 2Al indicates 2 moles of Al, and 2AlCl₃is referred to as 2 moles ofAlCl₃.

Step2. The following points define which types of information does a balanced chemical equation provides:

1). Identification of reactants and products

Example. In the above equation, Al and Cl₂ are reactants and AlCl₃ is the final product.

2). Physical states of reactants and products.

Example. (s) solid, (g) gas.

3). Mole ratios of reactants and products.

2 moles Al to 2 molesAl and 6 moles of Cl to 6 moles ofCl.