subject of study of thermodynamics is energy in all its forms, and, most importantly, the transfer of energy from one form to another.Historically, the term originated in the early days of research in the field of energy, and at that time a list of different types of energy was still small - mechanical and thermal.So called "thermodynamics" most accurately reflects the essence of the subject - the movement (transfer) and conversion of heat into mechanical work, and vice versa.Gradually the concepts of characterizing thermal processes: heat of fusion, heat capacity and, finally, the unit of measurement of heat - calorie (1772 M.Vilke).It will take a lot of time and will be formulated first law of thermodynamics, but each step was a result of hard work of many researchers.
To study the laws of thermodynamics taken some conventions how to isolate the investigated object and specify the properties to be investigated.The test objects are represented by closed systems of a large number of particles.If the s
basis of the theoretical apparatus of thermodynamics are 3 law.It is assumed that the body can absorb energy by increasing its internal (eg when heating) and / or at the expense of its internal energy to do work to overcome external forces (for example, pushing the piston).Based on this, the first law of thermodynamics is treated as follows: the change in internal energy of the body U is the amount of energy they absorbed energy Q and external forces A. Mathematically, this is expressed through the infinitesimal changes as follows:
dU = dQ + dA (1)
In fact, it is the law of conservation of energy, we can say, the law of life.
Features thermodynamic processes are usually considered in the model, where the working medium takes an ideal gas, which can be heated and / or take over it mechanical work of external forces (contraction - expansion) with the help of the piston, and one of the parameters - pressure P, volume V, orthe temperature T - is constant.Application of the first law of thermodynamics to izoprotsessam to determine the sources of energy receivers for specific conditions.
isochoric process means that V = const.The consequence of the fact that the mechanical work is absent, sincethe volume is not changed by the heat can increase the only internal energy, and then: dA = pdV = 0, and hence dU = dQ and determine its possible from the relationship:
dQ = (m / M) * CV * dT(2)
Thus, isochoric process is due to increase in temperature.
isobaric process involves p = const, and this condition is satisfied if the working fluid during heating performs mechanical work, such as the movement of the piston.If you turn to use the expression for the heating energy equation Mendeleev-Clapeyron, you can easily obtain an expression for calculating the mechanical operation of the gas:
A = (m / M) * R * (T2 - T1) (3)
R - the gas constantand means work to increase the volume of gas in an amount of one mole, if the temperature change of one degree Kelvin.Conclusion: the process of isobaric gas replenish energy heating (2), and spends part of the increased internal energy of the expansion (3).
process in which T = const, in thermodynamics is called isothermal.Its essence is that produced by the heating of the internal energy is completely consumed in the operation of preodoleniiyu external forces.The first law of thermodynamics for izoprotsessov suggests that to maintain a constant body temperature of its internal energy makes up for the cost of performing mechanical work, and depends on the pressure.Calculate these energy costs can be from expression:
Q = A = (m / M) * R * T * (ln (p1 / p2)).