In-Depth Notes for Chemistry Unit 5: Chemical Reactions

UNIT 5: APPLYING CHEMICAL REACTIONS

Key Definitions

• Solution: A homogeneous mixture of two or more substances.
• Solute: The substance that is dissolved in a solution.
• Solvent: The substance that dissolves the solute.
• Miscible: Liquids that can mix in any proportion (e.g., ethanol and water).
• Immiscible: Liquids that do not mix (e.g., oil and water).

Types of Solutions

• Gases in Liquids: E.g., carbon dioxide in carbonated drinks.
• Liquids in Liquids: E.g., vinegar in water.
• Gases in Gases: E.g., air (a mixture of nitrogen, oxygen, etc.).
• Solids in Liquids (Aqueous Solutions): E.g., salt in water.
• Solids in Solids (Alloys): E.g., brass (copper and zinc).

Influences on Solubility

1. Polarity:
   • "Like dissolves like" - polar solvents (e.g., water) will dissolve polar solutes and many ionic compounds.
2. Temperature:
   • Solubility often increases with temperature for solids in liquids but may decrease for gases.
3. Pressure:
   • Affects solubility of gases (higher pressure increases gas solubility).

Concentration of Solutions

• Molarity (M): Defined as moles per liter of solution.
  • Example: M = rac{ ext{moles of solute}}{ ext{liters of solution}}
  • For specific examples:
    • What is the molarity of a 500 mL solution made from 1.00 mole of CaCl2?
    • In a 2.00 M solution of CaCl2, what is the molarity of Cl- ions?

Practice Problems on Molarity

1. Calculate the molarity of NaCl in seawater (28.0 g/L).
2. Find molarity of 5.30 g of Na2CO3 in 400.0 mL.
3. Find volume (in mL) of 18.0M H2SO4 to obtain 2.45 g H2SO4.
4. Volume (in mL) of 12.0M HCl for 3.00 moles?
5. Molarity with 20.0 g H3PO4 in 50.0 mL?
6. Mass (in grams) of KCl in 2.50L of 0.50M solution?

Other Measurements of Concentration

• Molality (m): Moles of solute per kg of solvent.
• Mole Fraction: Ratio of moles of solute to the total moles of solution.
• Mass Percent, Parts per Million (ppm), Parts per Billion (ppb): Useful for trace substances.

Management of Concentration Calculations

• Understand dilution and how it relates to molarity: $C<em>1V</em>1 = C<em>2V</em>2$.
  • Example: Molarity of NaCl diluted from 5.00M in 525mL to 1L?

Kinetics and Reaction Rates

• Collision Theory:
  • Reactants must collide to react; collisions need sufficient energy and proper orientation.
• Factors Affecting Reaction Rate:
  1. Nature of Reactants
  2. Surface Area
  3. Temperature
  4. Concentration
  5. Catalysts

Equilibrium in Chemical Reactions

• Reversible Reactions:
  • Reactions can proceed in both forward and reverse directions, establishing equilibrium when rates are equal.
• Equilibrium Constant (K):
  • K = rac{[ ext{Products}]}{[ ext{Reactants}]}
• Practice writing equilibrium expressions for various reactions.

Redox Reactions

• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.
• Identifying Agents:
  • Oxidizing agent: causes oxidation and is reduced.
  • Reducing agent: causes reduction and is oxidized.

Balancing Redox Reactions

1. Write half-reactions for oxidation and reduction.
2. Balance the electrons transferred.
3. Combine half-reactions to get the overall reaction.

Electrochemical Cells

• Spontaneous redox reactions such as in a voltaic cell produce electric current.
• Anode: Electrode where oxidation occurs; Cathode: Electrode where reduction occurs.
• Salt bridge maintains charge balance between electrodes.

Preparation for the Exam

• Understand the principles of polarity, reaction rates, equilibrium, concentration calculations, and redox reactions.
• Practice problems relating to these concepts to improve comprehension and speed.