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Essential Concepts for Chemistry Unit 2

Oct 23, 2024

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Honors Chemistry Study Guide: Unit 2 Test

Key Concepts

Particle Diagrams

  • Cold vs. Hot Solids:
    • Cold solids: Particles are close together in an orderly fashion.
    • Hot solids: Particles show thermal expansion, slightly more spaced with exaggerated wush lines.
  • Liquids:
    • Cold liquid: Particles more spaced at the bottom with small wush lines.
    • Warm liquid: Particles more spread with exaggerated wush lines.
  • Gases:
    • Cold gas: Evenly distributed with small wush lines and pressure arrows.
    • Warm gas: Same distribution but with exaggerated wush lines and larger pressure arrows.
    • Note: Thermal expansion in gases is noted in flexible containers.

Unit Conversions

  • Pressure:
    • 1 ATM = 760 mmHg = 760 Torr.
    • Conversion examples:
      • 1802 mmHg to Torr: 1802 Torr (1:1 ratio).
      • 0.0028 ATM to Torr: 2.1 Torr using 760 Torr/ATM.
      • 91.2 inches Hg to ATM: Convert inches to mmHg using 2.54 cm/inch, then 1 ATM/760 mmHg. Result: 3.05 ATM.

Molar Mass Calculations

  • Propane (C3H8):
    • Molar Mass = 3(12.01) + 8(1.01) = 44.11 g/mol.
  • Cobalt Atoms in a Block:
    • 3.25 kg Cobalt, convert to grams, then to moles using 58.93 g/mol, then to atoms using Avogadro’s number. Result: 3.32 x 10^25 atoms.

Ideal and Combined Gas Laws

  • Ideal Gas Law for Non-changing Conditions:
    • Use PV=nRT when conditions do not change.
    • Example: Calculate volume of CO at given mass, temperature, and pressure.
  • Combined Gas Law for Changing Conditions:
    • Use when starting and final conditions are given (e.g., temperature change).
    • Example: Increase in pressure when a tank is warmed.

Conceptual Questions

  • Pressure Reduction Strategies:
    • Lower temperature or reduce gas particles to decrease pressure.
    • Increase volume to decrease pressure due to fewer collisions per area.

Atmospheric Pressure in Everyday Phenomena

  • Straw Function:
    • Reducing pressure inside a straw by removing air allows atmospheric pressure to push liquid up.
  • Can Crush Demonstration:
    • Hot gas cooled rapidly in a sealed can reduces internal pressure, causing the can to collapse.
  • Breathing Mechanism:
    • Diaphragm movement changes lung volume, influencing internal pressure to facilitate air movement.

Dimensional Analysis

  • Combustion of Methane to CO2:
    • Using conversion factors to determine volume of CO2 from given mass of CH4.
    • Example calculation from grams to liters based on molecule and density data.
    • Final result: 77.8 liters of CO2.

This guide summarizes the essential concepts and problem-solving steps needed for the Unit 2 test in Honors Chemistry, focusing on gases behavior under different conditions, conversions, and applications of gas laws.

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