First law: internal energy, work, heat
Chemical Thermodynamics · Chemistry
Study notes
A gas expands against 1 atm from 2 L to 5 L, absorbing 300 J heat. Find ΔU. Step 1: w = −P_ext ΔV = −(1.013×10⁵ Pa)(3×10⁻³ m³) = −304 J. Step 2: Work done BY system → negative in chemistry convention. Step 3: ΔU = q + w = 300 + (−304) = −4 J. Step 4: Internal energy barely changed — heat in ≈ work out. (Physics convention flips the sign: ΔU = q − w.)