Warming Up: Heat & Thermodynamics
Heat and thermodynamics study heat as a form of energy transfer and the laws of thermodynamics that govern energy transformations, revealing how energy flows and changes in systems. Heat transfers energy due to temperature differences, while the laws of thermodynamics dictate how energy, work, and entropy behave, providing a framework for understanding processes like engine efficiency, melting ice, and even the universe’s fate.
Overview of Heat & Thermodynamics
Heat and thermodynamics are defined by key concepts and principles of energy behavior. Here’s the breakdown:
- Heat Transfer: The movement of thermal energy due to temperature differences, via conduction, convection, or radiation.
- First Law of Thermodynamics: Energy conservation—energy cannot be created or destroyed, only transferred or transformed (ΔU = Q - W).
- Second Law of Thermodynamics: Entropy of an isolated system increases; heat flows from hot to cold spontaneously.
- Third Law of Thermodynamics: As temperature approaches absolute zero (0 K), the entropy of a system approaches a minimum.
Examples of Heat & Thermodynamics
Heat Transfer Examples
- Conduction: A metal spoon in hot soup warms up as heat conducts from the soup.
- Convection: Warm air rises in a heated room, creating a convection current.
- Radiation: The sun heats Earth through electromagnetic waves across space.
First Law of Thermodynamics Examples
- In a gas engine, 500 J of heat (Q) is added, 200 J of work (W) is done, increasing internal energy by 300 J (ΔU = Q - W).
- A melting ice cube absorbs 1000 J of heat with no work, raising its internal energy by 1000 J.
- Compressing a gas with 300 J of work while losing 100 J of heat decreases internal energy by 200 J.
Second Law of Thermodynamics Examples
- Ice melts in a warm room as heat flows from the room (hot) to the ice (cold).
- A refrigerator transfers heat from inside (cold) to outside (hot), but requires work from electricity.
- A car engine loses some energy as heat, increasing the entropy of the surroundings.
Third Law of Thermodynamics Examples
- At 0 K, a perfect crystal’s entropy is zero, as molecular motion ceases.
- Helium’s entropy approaches a minimum near absolute zero, but never fully reaches 0 K.
- Cooling a gas to near 0 K reduces its entropy to a minimal value.