in joules (J), where 1 J = 1 Pa·m3. PV work is an important topic in chemical thermodynamics. For a process in a closed system, occurring slowly enough for accurate definition of the pressure on the inside of the system's wall that moves and transmits force to the surroundings, described as quasi-static, work is represented by the following equation between differentials: where (inexact differential) denotes an infinitesimal increment of work done by the system, transferring energy to the surroundings; denotes the pressure inside the system, that it exerts on the moving wall that transmits force to the surroundings. In the alternative sign convention the right hand side has a negative sign. (exact differential) denotes an infinitesimal increment of the volume of the system. Moreover, where denotes the work done by the system during the whole of the reversible process. The first law of thermodynamics can then be expressed as (In the alternative sign convention where W = work done on the system, . However, is unchanged.) Path dependence PV work is path-dependent and is, therefore, a thermodynamic process function. In general, the term is not an exact differential. The statement that a process is quasi-static gives important information about the process but does not determine the P–V path uniquely, because the path can include several slow goings backwards and forward in volume, slowly enough to exclude friction within the system occasioned by departure from the quasi-static requirement. An adiabatic wall is one that does not permit passage of energy by conduction or radiation. The first law of thermodynamics states that . For a quasi-static adiabatic process, so that Also so that It follows that so that Internal energy is a state function so its change depends only on the initial and final states of a process. For a quasi-static adiabatic process, the change in internal energy is equal to minus the integral amount of work done by the system, so the work also depends only on the initial and final states of the process and is one and the same for every intermediate path. As a result, the work done by the system also depends on the initial and final states. If the process path is other than quasi-static and adiabatic, there are indefinitely many different paths, with significantly different work amounts, between the initial and final states. (Again the internal energy change depends only on the initial and final