Interactive Simulator · Thermodynamics

The first law: ΔU = q + W

Energy supplied to a gas as heat can do two things: raise its internal energy, or let it do work by pushing back a piston. The first law of thermodynamics keeps the books: the rise in internal energy equals the heat added plus the work done on the gas. Set the heat and the expansion, and watch the ledger balance.

Mission A gas is given 300 J of heat and does 200 J of work expanding. Predict its change in internal energy. Streak 0Best 0
With 300 J of heat in and 200 J of work done by the gas, ΔU is:
heat supplied to gas, q+300 J
work done by gas, pΔV200 J
change in internal energy ΔU = q − pΔV+100 J
Constant pressure p = 1.0 × 10⁵ Pa. In ΔU = q + W, the work done ON the gas is W = −pΔV, so ΔU = q − pΔV. Expansion (ΔV > 0) lets the gas do work, lowering ΔU.