If the system is not closed, the third mechanism that can increase the internal energy is transfer of matter into the system. This increase, Δ Δ U m a t t e r cannot be split into heat and work components. If the system is so set up physically that heat transfer and work that it does are by pathways separate from and independent of matter transfer, then the transfers of energy add to change the internal energy: Δ Δ U = Q − − W + Δ Δ U matter (matter transfer pathway separate from heat and work transfer pathways) .