First Law of Thermodynamics

[Jinsiang_Ong_3H]

Does anyone know why the first law of thermodynamics is sometimes listed as delta U = Q - W, but in Outline 3 the first law of thermodynamics is listed as delta U = Q - W? I think it has something to do with how the system and environment are perceived in relation to one another, but I'm not sure.

[Vishwa Diwan 1D]

I think you meant to ask why it can be Delta Q = W + U, and I think it is based on how the work is done and whether or not it takes from the system but both are equivalent to each other.

[Sandhya_Seetharaman_2A]

DeltaU = Q + W is just another way to write the first law because that way it makes more sense when considering the W part, since it is negative if work is being done by the system and is positive if work is being done to the system.

[Kylie Cheng 1G]

What are the different ways to write the first law of thermodynamics? I've been getting confused with the variety of ways that this law is represented.

[jhb123]

The first law of Thermodynamics relates to the conservation of energy. The change in the internal energy of the system is equal to the heat added to the system (Q) + the work done by the system (W). Every, in this sense, cannot be created or destroyed. It is "transferred" (converted) to an alternate form. The work done on the system (i.e pushing a chair) is converted to an alternate form of energy (i.e thermal energy on the ground, created by the "pushing" of the chair). This can be used to explain the values expressed in the equation, specifically how it relates to U (overall energy change).