First Law of Thermodynamics

Introduction

• Overview of previous thermodynamics videos in chemistry and physics playlists.
• Focus on the First Law of Thermodynamics.

First Law of Thermodynamics

• Statement: Energy cannot be created or destroyed, only transformed.
• Highlighted in magenta for emphasis.

Examples of Energy Transformation

Projectile Motion Example

• Scenario: Throwing a ball straight up.
• Energy Types:
  • Kinetic Energy: Energy due to the ball's motion when thrown.
  • Potential Energy: Energy at the peak of the throw where the ball's velocity is zero.
• Energy Transformation: Kinetic energy transforms into potential energy as the ball rises.

Air Resistance Effect

• Scenario: Ball thrown upward with air resistance.
• Kinetic Energy Change:
  • Initial kinetic energy (high) → Potential energy at peak (zero kinetic energy) → Less kinetic energy than initial upon returning to ground.
• Energy Loss Explanation: Energy lost due to air resistance transformed into heat by increasing the kinetic energy of air molecules.

Internal Energy of a System

• Definition: Internal energy (U) is the total energy within a system.
• Components of Internal Energy:
  • Kinetic energy of atoms/molecules.
  • Rotational energy (for molecules).
  • Potential energy of bonds.
  • Electrical potential energy of electrons.
  • Vibrational energy of particles.
• Assumption: Often simplified to focus on ideal monoatomic gases (e.g., helium, neon).

Change in Internal Energy

• Formula:
  • Change in internal energy (ΔU) = Heat added to the system (Q) - Work done by the system (W).
• Interpretation of terms:
  • Q: Heat transfer to/from the system.
  • W: Work done by the system or on the system.
• Positive Change in Internal Energy: Indicates energy is added to the system (either through heat or work).
• Negative Change in Internal Energy: Indicates energy is lost (through work done by the system or heat lost).

Alternative Formulas

• Different Notations:
  • ΔU = Q - W (work done by the system).
  • ΔU = Q + W' (work done on the system).
• Use common sense to interpret energy flow related to heat and work, rather than memorizing specific formulas.

Conclusion

• Summary of the First Law and its implications on energy transformations.
• Next steps: Further exploration of internal energy and its calculations in future videos.