”Energy cannot be created or destroyed it can ONLY be CHANGED from one FORM to another”
1st Law of thermodynamics & Albert Einstein.
The reason for the use of adjective ‘ONLY’ is to highlight the fact that whatever else is said about energy is not true, & for energy to be anything else there has to be a scientific proof (physics, thermodynamics, or any other branch of science).
Thermodynamics is the science of the relationship between HEAT, WORK & the PROPERTIES of system.
Energy cannot be; & is not
Energy cannot be renewable;
Energy has no source;
Energy cannot be dirty or clean;
Energy has no colour;
Energy cannot be green;
Energy is not a product,
Energy is not a commodity,
Energy is not something which is consumed;
Energy is not generated;
Energy cannot have a company or firm
Energy has no price;
Energy has no market,
Energy cannot be secure or insecure;
Energy is not a policeable thing
Energy has nothing to do with climate
For sure if energy was any of the above, no doubt 1st Law of thermodynamics , or any other law in thermodynamics; or indeed thermodynamics in general, as an expert knowledge, & subject area for energy; or, Albert Einstein; would have told us about the above list of myths or esoterica on energy.
Why Albert Einstein went out of his way & reiterated the 1st of thermodynamics? Well; because, Albert Einstein wanted to go on & say ”E=mc² where E = energy; m = mass & c speed of light.”
The 1st law of thermodynamics statement also shows: when considering energy one can ”ONLY” consider the ”CHANGE” & the ‘‘FORM’‘ of energy.
The relationship between the CHANGE & the FORM of energy is expressed mathematically in thermodynamics as:
The expression above can take more elaborate form if other FORMS of energy is included:
The 1st law of thermodynamics is also a statement that brings together 3 concepts in thermodynamics:
Heat Transfer : Fuel Burns (Combustion), Chemical Energy in Fuel CHANGES to Thermal Energy (Heat). Heat changes water to steam.
work transfer Kinetic Energy in Steam works on Turbine by rotating turbine . Turbine transfers work by rotating an electrical conductor across a magnetic field Generator
Energy Change. The difference between Heat & Work, i.e. Heat minus Work. The amount of Heat is always larger than amount of work. Energy is the mathematical concept relating Heat to Work, & becomes a unique ”property”; an observable characteristics for the power station as shown below: this thermodynamics calls a System
In thermodynamics, a ”property” is any (macroscopic) ”observable characteristic” of a ”system”; & in thermodynamics, a ”system” is any prescribed & identifiable collection of matter; & amoeba-like sketch below is the usual representation of one:
Energy like altitude, pressure, volume, temperature, density, enthalpy, entropy, exergy, & internal energy is a ”property” MIT calls ”energy” a ”useful property”
What is ”energy”?
The difference: Q – W; where Q = Heat & W= Work; or,
The sum of the Kinetic Energy & the Strain Energy for all the molecules; or,
“the CAPACITY for doing work”
Properties of properties
“Property” is “any observable characteristic of a system”. This will have three consequences 3 logical consequences of this definition, namely:
(i) The change in the value of a property of a system depends only on the end-states of the process and not on the path of the process.
(ii) If a magnitude related to a system changes during a process by an amount that depends only on the end-states and not on the path of a process, that magnitude is a property of the system.
(iii) In a cyclic process the net change in each property of a system is zero.
Definition of energy
The 1st Law implies the existence of a property, which will be called energy. Energy is defined as:
The increase of energy of a system during a change of state is numerically equal to the net heat during the process minus the net work during the process.
In symbols this definition is written as
where E1 and E2 are the energies of the system in the final state 2 and the initial state 1 respectively.
Proof that energy is a property
Figure 1 below is a diagram having arbitrary properties of a system, x and y, as abscissa & ordinate. (For definiteness, x and y might be thought of as volume and pressure respectively.) The points marked 1 & 2 represent two states of the system.
- Figure 1: Paths of cyclic processes passing
through two common state-points.
Consider a cyclic process executed by the system: it starts from state 1, proceeds to state 2 along the path marked A on Fig. CP, & returns to state 1 along the path C. From the 1st Law we can write:
wherein the summation around the cyclic process has been split into its component parts. The two integrals on the right-hand side of equation (Eq2) represent, respectively, the summation of the ‘heat’ & ‘work‘ during the change of state from ‘1′ to ‘2′ along path ‘A’, & the summation from ‘2′ to ‘1′ along path ‘C’.
Now consider a second cyclic process differing from the first only in that the outward path is the different one marked B on Fig. CP. Applying the 1st Law to this cyclic process, we obtain:
Combination of eq. (Eq2) and eq. (Eq3), yield
signifying that the integral of (dQ – dW) from state 1 to state 2 is the same for path A as for path B.
But all that has been specified about paths A & B is that they are different. It follows that:
If we now write
Then Eq5 becomes
Q – W
has the same value for any path between 1 & 2
But from the definition of energy (Eq1)
Therefore E2 – E1 has the same value for any path between l and 2
This means that E2 depends only on the end-states.
From what has been said earlier about the “properties of properties” consequence (ii) it follows that energy E is a property.
It is one thing to mystify an ”energy”; & go on about: Renewable Energy, Clean Energy, Green Energy, Sustainable Energy, etc, another to learn to use energy in engineering & yet another to attain that grasp of the concept which is called “understanding”.
It is amazing how widespread the use of thermodynamics is in our everyday lives; & It is amazing; & astonishing how widespread is the illiteracy in thermodynamics; & basic physics.
Surely the prerequisite to discuss energy, & matters relating to energy has to be, a certain degree of thermodynamics literacy; & basic understanding of physics