Thermodynamics

Thermodynamics is a discipline that deals with heat and work. It describes macroscopic quantities, such as heat, work, internal energy, enthalpy, entropy, Gibbs free energy, etc. Classical thermodynamics assumes that the world is made up of a continuum.

Quantum mechanics lies on the other end of the spectrum from classical thermodynamics. It deals with nanoscopic properties. Quantum mechanics gives rise to concepts such as the particle-wave duality², which states that all energy and all matter behaves both like a wave and like a particle. It tells us that energy and other quantities are not continuous, but discrete. The governing equation is the Schrö dinger equation³. The state of any system is described by the wave function, which is the solution of the Schrö dinger equation. Quantum chemistry typically deals with solving the Schrö dinger equation for single molecules, giving information on the electronic structure (how atoms are bonded together, how electrons are shared to make up chemical bonds) and the geometrical structure.

The term ‘statistical mechanics’ was coined by the greatest American scientist, J. Willard Gibbs. The basic idea of statistical mechanics is that one can take the properties, energy levels, probabilities of individual molecules from quantum mechanics and average these in an appropriate way to obtain the properties of a macroscopic collection of molecules. For example, if you know the probable states of a single isolated polymer then you can predict the thermodynamic properties of 10 kg of the polymer in an extruder⁴ by applying the techniques of statistical mechanics. Hence, statistical mechanics is the bridge between quantum mechanics (single molecules) and thermodynamics (continuum mechanics).

Intensive and extensive variables belong to the basics of thermodynamics. The difference between intensive and extensive properties is like the difference between “quality” and “quantity”. As an example, would you be excited if someone said he was going to give you 1 kg of gold? If one said that the gold was contained in 108 m³ of sea water you would probably be much less excited. The concentration in sea water is the “quality”, while the 1 kg is the “quantity”. For example, temperature is intensive, if one block of ice is at − 10º C; then adding another identical block does not make the temperature − 20º C, but it does mean that melting the two blocks of ice will take twice as much energy¹.

Thermodynamics, as well as any other discipline, has its own laws. The “Laws” of thermodynamics are not laws, but principles that have never been violated. These laws are very generally valid, can be applied to such systems as the balance of energy and matter transfer. These four laws are:

· Zeroth law of thermodynamics is about thermal equilibrium: If system A is in thermal equilibrium with system B, and system B is in thermal equilibrium with system C, then system A is in thermal equilibrium with system C.

· First law of thermodynamics is about the conservation of energy: The first law states that the energy in these processes is conserved, and heat can be converted into work and work into heat.

· Second law of thermodynamics is about entropy: The total entropy of any isolated thermodynamic system always increases over time, approaching a maximum value. Another way to phrase this: heat cannot spontaneously flow from a colder location to a hotter area - work is required to achieve this.

· Third law of thermodynamics is about the absolute zero of temperature: the Third law states that the absolute entropy is zero for any perfect crystalline substance at a temperature of absolute zero. This is only true when the crystalline phase does not have any energetic degeneracies. The third law also defines the concept of the zero of temperature. Without it, all temperature scales would be arbitrary.

As a system approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: " the entropy of all systems and of all states of a system is zero at absolute zero" or equivalently " it is impossible to reach the absolute zero of temperature by any finite number of processes". Absolute zero, at which all activity would stop if it were possible to happen, is − 273.15 °C, or − 459.67 °F or 0º K.

Notes to the text:

1. To take twice as much energy – затрачивать вдвое больше энергии

2. Particle-wave duality - корпускулярно-волновой дуализм. Это физический принцип, согласно которому любой объект может проявлять как волновые, так и корпускулярные свойства.

3. The Schrö dinger equation- уравне́ ние Шрёдингера. В квантовой физике это ключевое уравнение, связывающее пространственно-временное распределение с помощью представлений о волновой функции.

4. Extruder - экструдер (от лат. extrudo - выталкиваю), машина для размягчения материалов и придания им формы путём продавливания через профилирующий инструмент, сечение которого соответствует конфигурации изделия. В экструдере получают главным образом изделия из термопластичных полимерных материалов, используют их также для переработки резиновых смесей (в этом случае экструдер часто называют шприц-машиной).

5. − 459.67 °F; the Fahrenheit scale - шкала Фаренгейта, используемая в основном, в Англии и в США. Ноль градусов Цельсия — это 32 градуса Фаренгейта, а градус Фаренгейта равен 5/9 градуса Цельсия.

6. 0º K; the Kelvin scale - Шкала температур Кельвина, в которой начало отсчёта ведётся от абсолютного нуля.