Question

Write balanced molecular and net ionic equations for the following reactions in aqueous solution. (a) calcium + water calcium hydroxide + hydrogen (b) barium chloride \(+\) sodam sulfate barium sulfate \(+\) sodium chloride

Short answer

The balanced molecular equations are: \n (a) \(Ca + 2H2O -> Ca(OH)_2 + H_2\) and \n (b) \(BaCl_2 + Na_2SO_4 -> BaSO_4 + 2NaCl\). \n The net ionic equations are: \n (a) \(Ca + 2H_2O -> Ca^{2+} + 2OH^- + H_2\) and \n (b) \(Ba^{2+} + SO4^{2-} -> BaSO_4\).

Step-by-step solution

Balancing the first molecular equation

Write down the given chemical reactions using their chemical symbols: \n(a) \(Ca + H_2O -> Ca(OH)_2 + H_2\). This equation is not balanced as there are 2 hydrogen atoms on the left but 4 on the right, and 1 oxygen on the left but 2 on the right. To balance it, add a coefficient of 2 in front of \(H_2\) on the product side and \(H_2O\) on the reactant side. This leads to the balanced molecular equation \(Ca + 2H_2O -> Ca(OH)_2 + H_2\).

Writing first net ionic equation

Since Calcium and Water molecules are breaking down into ions, the net ionic equation would look like this. \n \(Ca + 2H_2O -> Ca^{2+} + 2OH^- + H_2\).

Balancing the second molecular equation

Similarly, write down the given chemical reaction using their chemical symbols for the second chemical reaction: (b) \(BaCl_2 + Na_2SO_4 -> BaSO_4 + 2NaCl\). The equation is balanced as it is, since there are equal numbers of each type of atom on both sides.

Writing second net ionic equation

Since Barium, Chlorine, Sodium and Sulphur are ions, the net ionic equation would look like this: \n \(Ba^{2+} + SO4^{2-} -> BaSO_4\). This is the net ionic equation because Sodium and Chlorine are spectator ions and do not participate in the reaction.

Key concepts

Net Ionic Equations

Net ionic equations are an essential part of understanding chemical reactions that occur in aqueous solutions. These equations showcase only the particles that participate in the actual chemical change, leaving out the 'spectator ions' that do not participate in the reaction.
When writing a net ionic equation, start by writing the molecular equation of the reaction and then express all the aqueous compounds as their respective ions. Identify the ions that appear on both sides of the equation without changing their state. These are your spectator ions.

• In the case of the given exercise, for the reaction between calcium and water, the net ionic equation is derived by isolating the ions that undergo change. Thus, the equation: \(Ca + 2H_2O \rightarrow Ca^{2+} + 2OH^- + H_2\).
• For the reaction involving barium chloride and sodium sulfate, the net ionic equation focuses just on the ions that produce a solid precipitate, barium sulfate, eliminating sodium and chloride ions as they remain in solution and unreacted, leading to: \(Ba^{2+} + SO_4^{2-} \rightarrow BaSO_4\).

By focusing on the reacting ions, net ionic equations provide a clearer picture of the chemical change taking place.

Molecular Equations

Molecular equations represent chemical reactions by displaying all reactants and products in their molecular form without showing their ionic characters. This kind of equation is useful for getting an overview of the substances involved in a chemical reaction.
In a molecular equation, compounds are written using their full chemical formula. This often involves balancing the equation by adjusting coefficients to ensure the law of conservation of mass is met, meaning the same number of atoms of each element should be on both sides of the equation.

• The molecular equation for calcium reacting with water is: \(Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2\). Initially, it was unbalanced, and we included coefficients to match the number of atoms on both sides.
• Meanwhile, the reaction between barium chloride and sodium sulfate is already balanced: \(BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl\), highlighting a different chemical process where a solid, barium sulfate, forms as the product of the reaction.

Molecular equations provide a straightforward way to write reactions but may not show the complete ionic nature of reactions that occur in solutions.

Balance Equations

Balancing chemical equations is a fundamental skill in chemistry that ensures mass and charge are conserved throughout the reaction. It's also crucial for deriving accurate net ionic and molecular equations.
To balance a chemical equation, make sure each side of the equation has the same number of each type of atom. Coefficients are used in front of compounds or elements to adjust their amounts, not subscripts, which could change the compounds themselves.

• For the reaction involving calcium and water, our initial equation \(Ca + H_2O \rightarrow Ca(OH)_2 + H_2\) was unbalanced, with mismatched numbers of hydrogen and oxygen atoms. The balanced form \(Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2\) ensures equal numbers of each atom on both sides.
• The reaction between barium chloride and sodium sulfate, \(BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl\), is inherently balanced as all atom types match on both reactant and product sides without the need for additional coefficients.

Balancing equations involves trial and error and sometimes a systematic approach, but it is a must for understanding chemical reactions fully. Only after balancing can one accurately proceed to write molecular and net ionic equations.