2/18/2023 0 Comments Workdone with differenet pressure![]() ![]() It all depends on the sign convention (positive or negative) for work, W. Watch out-this first law of thermodynamics equation is sometimes written with different signs. The change in the internal energy of the system, Δ U, or the change in how fast the molecules in our helium balloon are moving, depends on how much energy is transferred as mechanical work, W, and as heat, Q. For a confined ideal gas the first law of thermodynamics says that Δ U = Q + W. A great example is our trusty old Helium balloon. Instead we'll consider a simpler system, like a confined ideal gas. There are too many things that the water can do in our boiling pot of water system to consider the system "closed." Energy is still conserved, but you would need a very fancy equation to account for that big puddle on the windowsill. Heat can even leak out the sides of the pot itself. Steam escapes from our pot of water to heat up the entire kitchen and condense on the kitchen windows. However, it's not a good choice for applying the first law of thermodynamics, because the boiling pot isn't a closed system. The steam is doing work, W: it's lifting the lid of the pot.Ī pot of boiling water is a nice everyday example to explain internal energy, heat, and work. As the water boils more vigorously, and more water experiences a phase change and vaporizes, the lid on the pot starts rattling.
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