Explain that the change in the internal energy of a system is equal to the energy added or removed by heating plus the work done on or by the system, and recognise this as the first law of thermodynamics and that this is a consequence of the law of conservation of energy.

A gas in a sealed piston system absorbs 850 J of thermal energy and expands, doing 320 J of work on its surroundings. The diagram below shows the initial and final states of the system. Which fundamental principle is demonstrated by the change in internal energy of the gas?

A gas in a sealed cylinder receives 850 J of thermal energy while simultaneously performing 320 J of work on its surroundings by expanding against a piston. This process is best described by which statement?