First law of Thermodynamics Flashcards
The 1st law of TD states that
the energy of universe is constant (Law of Conservation of Energy)
General energy balance equation
accumulation of energy = (mass flow of energy) + (heat flow of energy) -(energy due to expansion/compression) + (energy due to shaft work) + (energy due to moving fluid)
Energy balance for closed systems
dU= Q - PdV
or
dU= Q + W
Sign Convention
+Q = endothermic
-Q = exothermic
+W = endergonic
-W = exergonic
Internal Energy (U)
total energy of the system in the molecular level
Translational Kinetic Energy
Energy associated with the kinetic energy of the molecules as it moves at a certain velocity through space
Vibrational Kinetic Energy
Energy associated with the back and forth motion of atoms in a polyatomic molecule about their common center of mass
Rotational Kinetic Energy
Energy associated with the rotation of the atoms in a polyatomic molecule about an axis
Spin Energy
Energy associated with the rotation of the subatomic particles about their axes
Equipartition theorem of energy
states that the total kinetic energy of a system is shared equally among its independent components once the system attains thermal equilibrium.
The total energy of a dilute monoatomic gas is
U = U(0) + (3/2)RT
The total energy of linear molecules that can roate about two axes
U = U(0) + (5/2)RT
The total energy of nonlinear molecules that can rotate about three axes
U = U(0) + 3RT
Heat Capacity at Constant Volume
dU = Q_v =(dU/dT)_v = C_vdT
and
C_v = (dU/dT)_v
Enthalpy
Measure of the total energy of a thermodynamic system
H = U + PV
Hess’ law of heat summation
If a reaction proceeds via several steps, the heat of the overall reaction is the same as the algebraic sum of the heats involved in various steps
Standard enthalpy of formation
heat involved in the formation of a compound from its elements in their most thermodynamically stable state
Standard enthalpy of combustion
heat released when one mole of a fuel was burned in the presence of oxygen gas to produce carbon dioxide gas and liquid water at 25C and 1 bar
Joule-Thompson Effect
describes the temperature change of a fluid when it is forced to flow through a valve or porous plug adiabatically which is known as throttling or isenthalpic process
Calorimetry
involves measurement of heat involved in a chemical reaction or physical change
Nozzle
device that increases the velocity of the fluid at the expense of pressure
diffuser
decreases the velocity resulting in an increase in pressure
Compressors, fans, and pumps
devices that increase the pressure of a fluid by the supply of work through a rotating shaft
Turbines
devices that generate work fro a flowing fluid
Throttling valves
Flow-restricting device
