FormuLab
Thermodynamics

First Law of Thermodynamics

The first law balances a system’s internal-energy change with heat and work transfers.

Study tools
Save, share, export, or report this formula.
Source & review

Difficulty

Intermediate

Read time

5 min

Prerequisites

Basic algebra, consistent units, and the stated model assumptions

Review statusNeeds review

Source

OpenStax, College Physics 2e, §15.1 (Paul Peter Urone and Roger Hinrichs)

OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.

Adapted from OpenFormulaGraph, under CC BY 4.0.

FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.

Definition
Understanding the core concept

The first law balances a system’s internal-energy change with heat and work transfers. A sign convention is essential because some textbooks define work into the system as positive instead.

Variables & Units
Understanding each component
SymbolMeaningUnits
Energy (internal energy change)
Heat added to the system
Work done by the system
Real-World Applications
Where this formula is used in practice

Energy balances

Find a closed system’s internal-energy change.

Heat and work

Track energy transferred through heat and work.

Worked Example
Step-by-step calculation with real numbers

Problem

A closed system receives 500 J of heat and does 200 J of work on its surroundings. Find its internal-energy change.

Given

Solution

1
2
3

Final Answer

FormuLab is a study reference. Verify formulas, units, assumptions, and course-specific conventions before relying on them.

Browse by category

See all
MathematicsPhysicsFluid MechanicsElectricalComputer ScienceEngineering