Question

Do either of the following reactions go to completion? If \(\mathrm{so}\) what factor(s) cause(s) cach to do so? (a) \(\mathrm{MgSO}_{3}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{MgCl}_{2}(a q)+\mathrm{SO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) \(3 \mathrm{Ba}(\mathrm{OH})_{2}(a q)+2 \mathrm{H}_{3} \mathrm{PO}_{4}(a q) \longrightarrow \mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}(s)+6 \mathrm{H}_{2} \mathrm{O}(I)\)

Short answer

Reaction (a) goes to completion because of gas \(\text{SO}_{2}\). Reaction (b) goes to completion due to solid \(\text{Ba}_{3}\text{(PO}_{4}\text{)}_{2}\).

Step-by-step solution

Identify Reaction (a)

Consider the first reaction: ewline ewline \(\text{MgSO}_{3}(\text{s}) + 2 \text{HCl}(\text{aq}) \rightarrow \text{MgCl}_{2}(\text{aq}) + \text{SO}_{2}(\text{g}) + \text{H}_{2} \text{O}(\text{l})\). ewline Identify the nature of each reactant and product.

Analyze the Products of Reaction (a)

Look at the products of the reaction. One of the products is \(\text{SO}_{2}\), which is a gas. The formation of a gas often drives a reaction to completion because it can escape the reaction mixture.

Identify Reaction (b)

Consider the second reaction: ewline ewline \(\text{3 Ba(OH)}_{2}(\text{aq}) + 2 \text{H}_{3} \text{PO}_{4}(\text{aq}) \rightarrow \text{Ba}_{3} \text{(PO}_{4}\text{)}_{2}(\text{s}) + 6 \text{H}_{2} \text{O}(\text{l})\). ewline Identify the nature of each reactant and product.

Analyze the Products of Reaction (b)

Look at the products of the reaction. One of the products is \(\text{Ba}_{3} \text{(PO}_{4}\text{)}_{2}\), which is a solid. The formation of a precipitate (solid) often drives a reaction to completion because it is not dissolved in the solution.

Conclusion

Both reactions go to completion. Reaction (a) is driven to completion by the formation of a gas \(\text{SO}_{2}\), while reaction (b) goes to completion due to the formation of a solid precipitate \(\text{Ba}_{3} \text{(PO}_{4}\text{)}_{2}\).

Key concepts

Gas Formation

When analyzing chemical reactions, gas formation is a key concept. In the first reaction given:
\text{\(MgSO_{3}(s) + 2 HCl(aq) \rightarrow MgCl_{2}(aq) + SO_{2}(g) + H_2O(l)\)},
one of the products is sulfur dioxide (\text{SO_{2}}), which is a gas.
The formation of a gas is a strong driving factor for reactions to go to completion. This is because gases can easily escape from the reaction mixture, and once they do, they no longer participate in the reaction. The removal of a product from the equilibrium shifts the reaction forward, according to Le Châtelier's Principle.
This principle states that a system in equilibrium will adjust to counteract the change when a change is introduced.
In the context of gas formation, as the gas is produced and leaves the reaction chamber, the reaction continuously shifts to produce more of the gas until the reactants are fully consumed.
This is why the reaction involving the formation of \text{SO_{2}(g)} drives it to completion.

• Fun fact: Some reactions are designed to produce gases to ensure they reach completion!
• Make sure to always consider the state of products when analyzing reactions.

Precipitate Formation

In the second reaction given:
\text{\(3 Ba(OH)_{2}(aq) + 2 H_{3}PO_{4}(aq) \rightarrow Ba_{3}(PO_{4})_{2}(s) + 6 H_{2}O(l)\)},
one of the products is barium phosphate (\text{Ba_{3}(PO_{4})_{2}}), a solid.
The generation of a solid product, known as a precipitate, can also drive a reaction to completion. Unlike gaseous products, precipitates form and settle down out of the reaction mixture.
This separation from the reactants means that the solid is no longer in the same phase and can’t participate in the reaction, further pushing the reaction forward, consistent with Le Châtelier's Principle.
The formation of a precipitate indicates that the ions or molecules in the solution come together to form a solid, which signifies the reaction's progression. This is especially the case in reactions involving ionic compounds in aqueous solutions. The solid product can be separated out via filtration, significantly lowering its concentration in the mixture and further favoring the reaction's completion.

• Precipitates are sometimes used in lab settings to indicate when a reaction has finished.
• Always check for the formation of solid products when studying chemical reactions.

Reaction Analysis

Understanding why and when chemical reactions go to completion involves a detailed analysis of the nature of reactants and products. Analyzing the reactions involves a few critical steps:

• Identify the reactants and products, including their states (solid, liquid, gas, aqueous).
• Understand factors such as gas formation and precipitate formation that drive reactions to completion.
• Apply principles such as Le Châtelier's Principle to predict the direction of the reaction.

For Reaction (a):
\text{\(MgSO_{3}(s) + 2 HCl(aq) \rightarrow MgCl_{2}(aq) + SO_{2}(g) + H_2O(l)\)}, analyzing shows that the formation of the gaseous product \text{SO_{2}(g)} drives the reaction to go to completion.
For Reaction (b):
\text{\(3 Ba(OH)_{2}(aq) + 2 H_{3}PO_{4}(aq) \rightarrow Ba_{3}(PO_{4})_{2}(s) + 6 H_{2}O(l)\)}, barium phosphate (\text{Ba_{3}(PO_{4})_{2}}) forms as a solid precipitate, driving the reaction to completion.
Properly understanding these concepts allows for accurate predictions and comprehension of chemical reactions in varying contexts, reinforcing the importance of both theoretical and practical knowledge in chemistry.

• Regular practice and application of these analysis techniques can strengthen your understanding of chemical reactions.
• Always consider equilibrium principles when assessing reaction progress.