Ch.7: Chemical Reactions and Precipitation Reactions

Q: What happens in every chemical reaction?

A: Atoms rearrange to form new substances; bonds are broken and formed; energy is absorbed or released.

Q: Give three everyday examples of chemical reactions.

A: Volcano eruptions, car engines starting, and laundry detergent reacting in water.

Q: What are signs a chemical reaction has occurred?

A:
1⃣ Color change
2⃣ Formation of solid (precipitate)
3⃣ Formation of gas (bubbles)
4⃣ Energy change (heat absorbed/released)
5⃣ Light produced

Q: What are examples of physical changes that are not chemical reactions?

A: Melting and boiling.

Q: What are the two main parts of a chemical equation?

A: Reactants (left side) and products (right side).

Q: What do the following physical state symbols mean?

A: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water).

Q: What are the rules for balancing chemical equations?

A:
1⃣ Same number of each atom on both sides.
2⃣ Only change coefficients (not subscripts).
3⃣ Check that total atoms balance.

Q: What are the steps to balance an equation?

A:

1. Write unbalanced skeleton equation.

2. Add physical states.

3. Balance one element at a time.

   1. Check coefficients and totals.

Q: What is a solution?

A: A homogeneous mixture.

Q: Define solute and solvent.

A:

• Solute = the substance being dissolved.

• Solvent = the substance doing the dissolving.

Q: What is an aqueous solution?

A: A solution where water is the solvent.

Q: What happens when ionic compounds dissolve in water?

A: They dissociate into ions.

Q: What are strong vs. weak electrolytes?

A:

• Strong electrolytes fully dissociate and conduct electricity.

• Weak/non-electrolytes partially dissolve or not at all.

Q: What does “soluble” mean?

A: A compound dissolves in water.

Q: What does “insoluble” mean?

A: A compound does not dissolve in water.

Q: What law is followed when balancing chemical equations?

A: The Law of Conservation of Mass.

Q: What are the major takeaways for reactions and solubility?

A:

• Reactions rearrange atoms to form new substances.

• Observable signs identify reactions.

• Equations must balance.

• Electrolytes conduct current.

  • Solubility rules predict precipitates.

Q: What is a precipitation reaction?

A: A reaction where two aqueous ionic solutions form an insoluble solid (precipitate).

Q: What is the solid formed in a precipitation reaction called?

A: A precipitate.

Q: What is the rule for precipitation reactions?

A: Only insoluble compounds form precipitates; if all products are soluble, it’s “no reaction (NR).”

Q: Example of a precipitation reaction?

A: Mixing Pb(NO₃)₂ and KI forms yellow PbI₂ precipitate.

Q: Everyday example of a precipitation reaction?

A: Laundry detergent’s carbonate ions react with Ca²⁺ and Mg²⁺ in hard water to form solids, softening water.

Q: What are the steps to predict a precipitation reaction?

A:
1⃣ Identify ions in each aqueous reactant.
2⃣ Swap ions (cation from one with anion from the other).
3⃣ Check solubility rules for products.
4⃣ If one product is insoluble → precipitate forms; if both soluble → NR.
5⃣ Write physical states and balance the equation.

Q: What tool is used to predict solubility?

A: Solubility rules.

Q: What is a molecular equation?

A: Shows all compounds with complete formulas.

Q: What is a complete ionic equation?

A: Shows all ions present in the reaction solution.

Q: What are spectator ions?

A: Ions that appear on both sides of an ionic equation and do not change.

Q: What is a net ionic equation?

A: Shows only the ions that actually participate in forming the precipitate.

Q: Example of a net ionic equation?

A: Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s).

Q: What are the main ideas to remember about precipitation reactions?

A:

• They form an insoluble solid from two aqueous solutions.

• Use solubility rules to predict products.

• Always balance and include physical states.

• Spectator ions are omitted from net ionic equations.

• Only insoluble products appear in the net ionic equation.

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