OnRamps Chemistry Practice Exam Review

Instructor Introduction

• Instructor: Dave Laude
• Topic: Practice Exam 2 from Unit 4 on Thermodynamics
• Focus: Advanced thermodynamics calculations including:
  • Bond energies
  • Heats of formation
  • Second law of thermodynamics
  • Entropy in processes
  • Free energy

Exam Structure

• Refresher Questions: About 1/3 of questions are similar to previous exams.
• Advanced Calculations: Focus on table data and entropy problems.

Key Concepts Covered

Isolated Systems

• In isolated systems, neither heat nor energy flows.

First Law of Thermodynamics

• Internal energy is conserved.
• Internal energy of system + surroundings is conserved.
• Signs of system and surroundings energy are different.

Work Calculation

• Calculate using: -PΔV (pressure * change in volume).
• Example: 20 atm pressure, 0.1 L change, results in 200 J of work.*

Energy Calculations

• Q + W Calculation: Internal energy change related to heat and work.
  • E.g., a change of 500 KJ with work done resulting in -450 KJ on surroundings.

Calorimetry Calculations

• MCΔT for energy released by substances.
• Account for calorimetry housing.

Reaction Enthalpy Problems

• Rearrange reactions to find ΔH.
• Example: Adjusting reactions leads to ΔH of 400 KJ.

Entropy and Second Law

• Entropy Changes: Solids to gases increase entropy.
• Entropy of Universe: ΔS_universe = ΔS_system + ΔS_surroundings.
  • ΔS_surroundings determined by ΔH_system / T.

Bond Energy Problems

• Careful calculation of bond formation and breaking.
• Example: Combustion reactions involve negative energy changes.

Spontaneity and Free Energy

• ΔG = ΔH - TΔS.
• Reaction spontaneity depends on temperature.
• Example: Exothermic reactions become less likely as temperature increases.

Exam Tips

• Review Exam 1: Many similar questions appear.
• Calculation Proficiency: Be skilled in converting units and basic math.
• Understanding Theory: Especially around entropy and spontaneity.

Conclusion

• Best of luck on the exam, ensure mastery of these concepts for success.