First Law of Thermodynamics

Energy Conservation Simulator • ΔU = Q − W

Piston-Cylinder Apparatus

Isobaric Process System Ready
Temp (T) 300.0 K
Press (P) 101.3 kPa
Vol (V) 2.46 L

Parameter Controls

500 J
Quick Add Q:
100 J/s
101.3 kPa
300 K
2.46 L

Energy Balance Meter

ΔU = Q − W Verified
Heat Supplied (Q) +0.0 J Energy entering system
=
Internal Energy (ΔU) +0.0 J n · Cv · ΔT
+
Work Done (W) +0.0 J ∫ P dV
Q > 0 Heat Added
W > 0 Work done BY gas (Expansion)
ΔU > 0 Gas Temp & Internal Energy Rises
Error: 0.00 J

Energy Flow Diagram

Heat Input Q
0.0 J
Thermodynamic System
Gas Chamber
Internal Energy ΔU
0.0 J
Work Output W
0.0 J

Real-Time Process Graphs

Experiment Observation Table & Trial Logging

Trial # Process Mode Heat Q (J) Work W (J) ΔU (J) T₀ → T_final (K) P₀ → P_final (kPa) V₀ → V_final (L) Verification
No trials recorded yet. Set heat/load parameters and click Log Current Trial.

Educational Guide & Real-World Applications

Statement of the First Law

The First Law of Thermodynamics is the law of conservation of energy applied to thermodynamic systems. It asserts that energy cannot be created or destroyed; it can only be converted from one form to another or transferred between a system and its surroundings.

ΔU = Q − W

Term Breakdown

  • Q (Heat Transfer): Energy transferred across the system boundary due to a temperature difference.
  • W (Work Output): Energy transferred across boundary via mechanical force acting through displacement (W = ∫ P dV).
  • ΔU (Internal Energy Change): Total microscopic kinetic and potential energy of gas molecules. For an ideal gas: ΔU = n Cv ΔT.

Key Thermodynamic Processes

  • Isobaric (P = constant): Gas expands against fixed load (W = P ΔV). Q = ΔU + W.
  • Isochoric (V = constant): Piston is locked (W = 0). All heat goes into internal energy: Q = ΔU.
  • Isothermal (T = constant): Internal energy remains constant (ΔU = 0). Q = W.
  • Adiabatic (Q = 0): System insulated. Work done reduces internal energy: ΔU = −W.

Positive Values (+)

  • +Q: Heat added TO the system (increases system energy).
  • +W: Work done BY the system on surroundings (gas expands, pushing piston outward).
  • +ΔU: Internal energy INCREASES (temperature of gas rises).

Negative Values (−)

  • −Q: Heat removed FROM the system (cooling).
  • −W: Work done ON the system by surroundings (external force compresses gas).
  • −ΔU: Internal energy DECREASES (temperature drops).

State vs Path Functions

Internal Energy (U) is a state function—its value depends strictly on current state variables (T, P, V). In contrast, Heat (Q) and Work (W) are path functions—their values depend on the specific thermodynamic process path taken.

Steam Engines & Boilers

Heat input Q from combustion generates high-pressure steam that performs expansion work W on a heavy piston or turbine blades.

Air Compressors

Mechanical work W is done ON the gas (negative work), increasing internal energy ΔU and boosting air pressure for industrial tools.

Gas Turbines & Jet Engines

Combustion adds heat Q at high pressure; hot gas expands rapidly through turbine stages performing continuous shaft work W.

Internal Combustion Piston Engines

Fuel combustion inside cylinder delivers sudden heat burst Q, rapidly pushing the piston down to turn the crankshaft.

Heat Exchangers & Radiators

Fluid heat exchange (Q) changes fluid enthalpy and temperature without mechanical work output (W = 0).

Industrial Energy Audit

First law energy balance balances input fuel energy against useful mechanical work and waste heat thermal losses.

Check Your Understanding

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