Heat And Work; LibBook: E Brian Smith Flashcards
Heat
Transfer of energy that results in temperature differences
When two bodies of different temperatures str brought into contact, heat will flow until the temperature gradient disappears and the two bodies a reach the same temperature and thermal equilibrium is achieved.
Work done by the system is given a negative sign, as doing that work,
Work
Always completely convertible into the lifting of a weight
The work a system does by expanding, pushing back atmospheric pressure, or,conversely, the energy it gains when its volumes is reduced under atmospheric pressure.
Work done by the system is negative, as it loses energy by doing that work.
w = - S FdL
External Pressure
w = -S (PexA)dL = -S PexdV
If the external pressure, Pex, is always adjusted to be equal to the internal pressure of the gas within during the expansion, the system does the maximum amount of work
Electrical Work
w = -S ΦdQ
This work can be obtained from electrochemical cells. We will assume that the only work done by the physicochemical systems is the PV- work.
The work or expansion against the prevailing atmospheric pressure
Energy of a system
When transferred, both heat and work change the energy of the system. Heat and work are ways in which energy is transferred. The total change of a system, ΔU, is the net result of heat absorbed, q, and work done on the system, w (Or,i if energy lost, the heat evolved and the work done by the system)
ΔU = q=w
Overall
Going from on state to another, the energy change will always be the same but it may result from different quantities of heat and work being transferred to the system.
Work and heat are fundamentally different in that work can always be used to generate an equivalent amount of heat, but the converse is not true.
Heat can only be used to produce part of its energy in the form of work.
