🔥 Thermodynamics Basics

🌐 System & Surroundings

System = The part we’re studying (e.g., chemicals in a beaker).
Surroundings = Everything outside the system (e.g., the room).
Universe = System + Surroundings
Fun fact: The boundary can be real (like glass) or imaginary!

📦 Types of Systems

  • 🚪 Open System: Exchanges both energy and matter (e.g., open beaker).
  • 🔒 Closed System: Exchanges energy but not matter (e.g., sealed copper container).
  • ☢️ Isolated System: No exchange of energy or matter (e.g., thermos flask).
System types: Open (arrows in/out), Closed (energy arrows only), Isolated (no arrows)

📌 State of a System

Defined by state functions like:
– Pressure (\( p \))
– Volume (\( V \))
– Temperature (\( T \))
– Amount (\( n \))
Key point: Their values only depend on the current state, not how you got there! 🌟
Example: Water volume in a pond is the same whether filled by rain, tube well, or both.

⚡ Internal Energy (\( U \))

The total energy stored in a system (chemical + electrical + mechanical, etc.).
Changes when:
– Heat (\( q \)) flows in/out 🔥
– Work (\( w \)) is done on/by the system 💪
– Matter enters/leaves (in open systems)
Super important: \( U \) is a state function! 🎯

Changing Internal Energy

  • Via work (\( w \)): In adiabatic systems (no heat transfer): \[\Delta U = w_{ad}\] Signs: \(+w\) = work done on system (↑ energy), \(-w\) = work done by system (↓ energy).
  • Via heat (\( q \)): Through conducting walls: \[\Delta U = q \quad \text{(at constant volume, no work)}\] Signs: \(+q\) = heat absorbed (↑ energy), \(-q\) = heat released (↓ energy).

⚖️ First Law of Thermodynamics

The energy conservation law:
\[\Delta U = q + w\] Translation: Change in internal energy = heat added + work done on system.
✨ Golden rule: \( \Delta U \) depends only on initial/final states, while \( q \) and \( w \) depend on the path!
Big idea: Energy of an isolated system is constant (it can’t change!).

💨 Pressure-Volume (PV) Work

Example: Gas in a cylinder with a piston.
– Work is done on the gas when compressed by external pressure (\( p_{ex} \)).
– Work magnitude = area under \( p_{ex} \) vs. \( V \) curve.
Graph: Work = shaded area under p_ex vs ΔV

🚀 NEET Super-Ready Concepts

  1. System types (Open/Closed/Isolated) + real-life examples (beaker/flask).
  2. State functions: \( U, p, V, T \) (path-independent!).
  3. First Law: \(\Delta U = q + w\) + sign conventions.
  4. Adiabatic process: \( q = 0 \) → \(\Delta U = w_{ad}\).
  5. Internal energy changes via work/heat.

💡 Problem Tip

Example: If a system absorbs heat (\( q \)) and does work (\( w \)):
\[\Delta U = q – w \quad \text{(for a closed system)}\]
Why? Because \( w \) done by the system is negative in \(\Delta U = q + w\)!