Question

The first law of thermodynamics is usually written as dq=dw+du. you need to look at the signs carefully; some other disciplines (chemistry comes to mind) may use other signs, which implies other definitions of these quantities.

Answer 1

The first law of thermodynamics is follows the quantity dQ = dW + dU where Q is the heat flow, W is the work and U is the internal energy. Only the internal energy is a state function where it means that it does not follow a specific path to arrive at a certain number. Whereas the work and heat are not state functions and they follow a specific path or process in order to arrive at a certain number. An example would be if you are given 2,380 J of energy to do work as 12,900 J and you are to find the internal energy. Apply the equation above:

Q = U + W
2,380 J = U + 12,900 J
U = 15,280J.