Calculator · Thermal Engineering
Closed-System First Law
A fixed mass exchanges heat and work with its surroundings: ΔU = Q − W. Supply two of the three to solve the third, or all three to check that they balance. Heat into the system is positive; work done by the system is positive.
Inputs
ΔU = Q − W. Q > 0 is heat added to the system; W > 0 is boundary work done by the system on its surroundings, so a compression has W < 0.
Results
ΔU
60 kJ
| ΔU | 60 kJ |
|---|---|
| Q (into the system) | 100 kJ |
| W (by the system) | 40 kJ |
| Heat direction | into the system |
| Work direction | done by the system |
Assumptions
- · closed system
- · Q > 0 into the system
- · W > 0 done by the system
Technical reference
ΔU = Q − W
Q = ΔU + W, W = Q − ΔU
- ΔU
- change in internal energy[J]
- Q
- heat added to the system[J]
- W
- work done by the system[J]
Kinetic and potential energy of the system as a whole are not included.
Zero heat or zero work is valid; three values that do not balance are refused, not averaged.