Heat Released

[Ashley Hiti 1K]

Dr. Lavelle mentioned that sometimes the heat released is not available to do work. In what situations does that happen? Why would the heat not be available to do work?

[Bryan Cheng 1H]

If the heat simply dissipates into the surroundings (air, container, etc) it is not available to do work, which may be defined as mechanical or other action on something else. Steam engines function by having heated steam do work on a piston. If the steam simply heated up its container's walls, it would cool down and would therefore be unavailable to do work on the piston.

[Ethan Hung 2A]

When Prof. Lavelle was talking about the chemical in an open beaker, the heat may cause some of the chemical to become a gas and thus push against the atmospheric gases, thus doing work. In a sealed beaker, the gas cannot be pushed out and only the pressure increases without changing the volume (the equation for work is W = -PΔV).

[Alan Nguyen 2I]

It is not possible to convert all the energy absorbed by a system into work. Some of the heat is lost into the container and will not be available to convert into work.

[Abby Citro 2A]

If heat is released in an environment that is not completely controlled, it can escape into the atmosphere or be absorbed into the container, preventing it from doing work.