First Law of Thermodynamics (ΔQ = ΔU + ΔW)
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ΔQ = ΔU + ΔW
What each symbol means
| Symbol | What it stands for |
|---|---|
| ΔQ | Heat supplied to the system by surroundings (J) |
| ΔU | Change in internal energy of the system (J) |
| ΔW | Work done by the system on surroundings (J) |
When to use this
Applies to a closed system (no mass exchange across boundary). Energy conservation: heat supplied to system equals change in internal energy plus work done by the system on surroundings. Valid for all thermodynamic processes — reversible or irreversible.