key term - Double displacement reaction

Definition

A double displacement reaction, also known as a double replacement or metathesis reaction, occurs when the anions and cations of two different compounds exchange places to form two new compounds. This type of reaction often takes place in aqueous solutions and typically results in the formation of a precipitate, gas, or water, especially when one of the products is insoluble in the solution.

5 Must Know Facts For Your Next Test

1. In double displacement reactions, one of the products is often a solid precipitate that forms and settles out of the solution, which can be observed visually.
2. These reactions are driven by changes in enthalpy and entropy, with the formation of products that are more stable than the reactants being favored.
3. The driving force behind many double displacement reactions is the formation of a weak electrolyte or a non-electrolyte, such as water or a precipitate.
4. Double displacement reactions can also occur in acid-base neutralization processes, where an acid reacts with a base to produce salt and water.
5. When writing double displacement reactions, it’s important to balance both sides of the equation to adhere to the law of conservation of mass.

Review Questions

• How does a double displacement reaction lead to the formation of a precipitate, and what role does solubility play in this process?
  • In a double displacement reaction, if one of the products formed is an insoluble compound, it will precipitate out of the solution. The solubility rules help predict whether a particular combination of ions will produce a precipitate; for example, most sulfides and carbonates are insoluble in water. When soluble ionic compounds react, if the resulting product has low solubility, it will exceed its solubility limit and form a solid precipitate.
• Discuss how the common ion effect influences the outcomes of double displacement reactions involving sparingly soluble salts.
  • The common ion effect can significantly influence double displacement reactions by decreasing the solubility of sparingly soluble salts. When a common ion is added to a solution containing that salt, it shifts the equilibrium position according to Le Chatelier's principle, favoring the formation of more solid product. This effect can lead to increased precipitation and allows chemists to manipulate reaction conditions to drive desired outcomes in double displacement reactions.
• Evaluate the importance of double displacement reactions in real-world applications and how they relate to broader chemical processes.
  • Double displacement reactions play a crucial role in various real-world applications, including water treatment processes where contaminants are removed via precipitation. They are also fundamental in chemical synthesis and analytical chemistry for identifying ions in solution. Understanding these reactions helps in predicting behavior in complex mixtures and enhances knowledge about equilibrium systems in broader contexts such as environmental science and industrial chemistry.

Related terms

Precipitation reaction: A precipitation reaction is a specific type of double displacement reaction where two soluble salts react to form an insoluble salt that precipitates out of the solution.

Solubility product constant (Ksp): The solubility product constant is an equilibrium constant that provides insight into the solubility of ionic compounds in water, indicating whether a precipitate will form under given conditions.

Common ion effect: The common ion effect describes the decrease in solubility of an ionic compound when a common ion is added to the solution, influencing the extent of double displacement reactions involving that compound.