Change in energy of a closed system

[Nidhi Thati 3I]

The change in energy of a closed system is equal to q + w. Is work done when the system is compressed, and what is q in this? I know it results from the system being heated, but I was a little confused on the distinction between q and w.

[Yanaa_Mehra_1K]

Yes, when a system is compressed, work is done on the system and its internal energy increases. q is the heat transfer into or out of the system. if heat is transferred to the system it is +q, and if given out then -q. Similarly with work. If work is done on the system, it is +w and if done by the system, then -w. Both change the energy of the system but the only difference is that sometimes some of the energy is used up in the form of doing some work in the form of expansion or energy added by being compressed.

[Jennifer Jin]

Work is positive if work is done on a system (giving it energy) while work becomes negative if the system does work on the environment (decompressing).