First law of thermodynamics
Heat absorbed and work done all end up in the internal-energy account.
The increase in a gas's internal energy, ΔU, equals the heat Q it absorbs from its surroundings plus the work W the surroundings do on it. With the same 150 J input: at constant volume it all becomes internal energy; in isobaric expansion about 40% goes into work done by the gas; in isothermal expansion it all goes into work done by the gas and the internal energy stays the same; in adiabatic compression all the work done on the gas becomes internal energy and the gas heats up.
Energy vs. time
At every moment, ΔU = Q + W.
Think about it
Absorbing the same 150 J of heat, does the temperature rise more at constant volume or at constant pressure?
At constant volume. There W = 0, so all the heat becomes internal energy; in isobaric expansion the gas also does work, so only 3/5 becomes internal energy and the temperature rises less. This is also why the specific heat at constant pressure is larger than at constant volume.
Model assumptions0.1 mol of monatomic ideal gas, initially 300 K, 1 L · Processes are slow (quasi-static) · For isochoric, isobaric and isothermal processes E is the heat absorbed; for adiabatic, E is the work done on the gas; negative values mean heat released or work done by the gas
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.