Types of Energy in Gas Molecules

• Translational Kinetic Energy:
  • Present due to the movement of gas molecules.
  • Sometimes called regular kinetic energy.
• Rotational Kinetic Energy:
  • Exists in diatomic or polyatomic molecules, not in monatomic gases.
  • Molecules can rotate about a center point.
• Vibrational Energy:
  • Found in molecules with bonded atoms (e.g., diatomic molecules).
  • Atoms oscillate like masses on a spring.

Internal Energy of Gas

• Internal Energy (U):
  • Sum of all energy forms (kinetic, rotational, vibrational) in a gas.
  • Changes in internal energy affect molecule speed and rotation.

First Law of Thermodynamics

• Addresses how to change a gas's internal energy.
• Equation: ΔU = Q + W
  • ΔU: Change in internal energy.
  • Q: Heat added to the system.
  • W: Work done on the system.

Ways to Change Internal Energy

1. Heat (Q):
   • Heat enters the gas, increasing internal energy.
   • Energy transferred by particle collisions upon heating.
2. Work (W):
   • Work done by compressing the gas with a piston.
   • Compression adds energy to the gas, increasing internal energy.

Heat and Work Details

• Heat (Q):
  • Positive when entering the system.
  • Negative when leaving the system.
• Work (W):
  • Positive if work is done on the gas (piston moves down).
  • Negative if gas does work on the surroundings (piston moves up).

Understanding Work

• Work done on gas vs. by gas:
  • Work done on gas is positive and increases internal energy.
  • Work done by gas is negative and decreases internal energy.
  • The two are equal but opposite in sign.

Significance of the First Law

• Reflects the principle of energy conservation.
• Initially developed when the nature of heat was misunderstood.
• Critical for solving thermodynamic problems, understanding how energy transfers affect gas systems.