For non-constant pressure, the work can be visualized as the area under the pressure-volume curve which represents the process taking place.
Refrigerators, Heat pumps, Carnot cycle, Otto cycle
The change in internal energy of a system is equal to the head added to the system minus the work done by the system:
dE = Q - W (2)
dE = change in internal energy
Q = heat added to the system
W = work done by the system
1st law does not provide the information of direction of processes and does not determine the final equilibrium state. Intuitively, we know that energy flows from high temperature to low temperature. Thus, the 2nd law is needed to determine the direction of processes.
Enthalpy is the "thermodynamic potential" useful in the chemical thermodynamics of reactions and non-cyclic processes. Enthalpy is defined by
H = U + PV (3)
H = enthalpy
U = internal energy
P = pressure
V = volume
Enthalpy is then a precisely measurable state variable, since it is defined in terms of three other precisely definable state variables.
Go to Thermodyamics key values internationally agreed, Standard state and enthalpy of formation, Gibbs free energy of formation, entropy and heat capacity and Standard enthalpy of formation, Gibbs energy of formation, entropy and molar heat capacity of organic substances for listing of values for a lot of inorganic and organic substances.
Entropy is used to define the unavailable energy in a system. Entropy defines the relative ability of one system to act to an other. As things moves toward a lower energy level, where one is less able to act upon the surroundings, the entropy is said to increase. Entropy is connected to the Second Law of Thermodynamics.
For the universe as a whole the entropy is increasing.
Work, heat and energy systems.
Entropy and disorder.
The efficiency of the Carnot cycle.
Heat of combustion (energy content) for som common substances - with examples how to calculate heat of combustion.
Energy is the capacity to do work.
Energy balance and energy payback ratio.
Fluid energy transfer.
The mechanical, thermal, electrostatic, phase or chemical states of equilibrium.
Heat vs. work vs. energy.
The Mechanical Energy Equation compared to the Extended Bernoulli Equation.
Definition and explanation of the terms standard state and standard enthalpy of formation, with listing of values for standard enthalpy and Gibbs free energy of formation, as well as standard entropy and molar heat capacity, of 370 inorganic compounds.
Standardized enthalpies and entropies for some common substances.
Explanation of symbols used as subscripts or superscripts to tell more about the type of chemical reaction, process or condition.
Internationally agreed, internally consistent, values for the thermodynamic properties (standard enthalpy of formation, entropy and [H°(298)-H°(0)]) of key chemical substances.
Common thermodynamic terms and functions - potential energy, kinetic energy, thermal or internal energy, chemical energy, nuclear energy and more.
The entropy of a substance is zero if the absolute temperature is zero.
Definition and examples of calculation of weighted average bed temperature in adiabatic reactors.
Enthalpy-entropy diagram for water and steam.
Work done by a force acting on an object.
The direction of heat flow.
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