Thermodynamics Introduction Lecture (1) PDF

Al-Farabi University Department of petroleum engineering 2nd Stage Thermodynamics Introduction lecture (1) By Dr.Abdulazeez Basim What is Thermodynamics? Thermodynamics in physics is a branch that deals with heat, work, and temperature, and their relation to energ...

Al-Farabi University Department of petroleum engineering 2nd Stage Thermodynamics Introduction lecture (1) By Dr.Abdulazeez Basim What is Thermodynamics? Thermodynamics in physics is a branch that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. Specifically, it explains how thermal energy is converted to or from other forms of energy and how matter is affected by this process. What is thermal energy? Thermal energy is the energy that comes from heat. This heat is generated by the movement of tiny particles within an object, and the faster these particles move, the more heat is generated. Figure 1: Hot Source & Cold Sink Distinction Between Mechanics and Thermodynamics: In mechanics, we solely concentrate on the motion of particles or bodies under the action of forces and torques. On the other hand, thermodynamics is not concerned with the motion of the system as a whole. It is only concerned with the internal macroscopic state of the body. Different Branches of Thermodynamics: Thermodynamics is classified into the following four branches: 1) Classical Thermodynamics 2) Statistical Thermodynamics 3) Chemical Thermodynamics 4) Equilibrium Thermodynamics Classical Thermodynamics: In classical thermodynamics, the behaviour of matter is analyzed with a macroscopic approach. Units such as temperature and pressure are taken into consideration, which helps the individuals calculate other properties and predict the characteristics of the matter undergoing the process. Statistical Thermodynamics: In statistical thermodynamics, every molecule is under the spotlight, i.e. the properties of every molecule and how they interact are taken into consideration to characterize the behaviour of a group of molecules. Chemical Thermodynamics: Chemical thermodynamics is the study of how work and heat relate to each other in chemical reactions and in changes of states. Equilibrium Thermodynamics: Equilibrium thermodynamics is the study of transformations of energy and matter as they approach the state of equilibrium. Figure 2: Thermodynamic Systems System: A thermodynamic system is a specific portion of matter with a definite boundary on which our attention is focused. The system boundary may be real or imaginary, fixed or deformable. There are three types of systems: Isolated System – An isolated system cannot exchange energy and mass with its surroundings. The universe is considered an isolated system. Closed System – Across the boundary of the closed system, the transfer of energy takes place, but the transfer of mass doesn’t take place. Refrigerator, compression of gas in the piston-cylinder assembly are examples of closed systems. Open System – In an open system, the mass and energy both may be transferred between the system and surroundings. A steam turbine is an example of an open system. Table1: Interactions of thermodynamic systems Surrounding: Everything outside the system that has a direct influence on the behaviour of the system is known as a surrounding. Thermodynamic Process: A system undergoes a thermodynamic process when there is some energetic change within the system that is associated with changes in pressure, volume and internal energy. There are four types of thermodynamic processes that have their unique properties, and they are: Adiabatic Process – A process where no heat transfer into or out of the system occurs. Isochoric Process – A process where no change in volume occurs and the system does not work.  Isobaric Process – A process in which no change in pressure occurs. Isothermal Process – A process in which no change in temperature occurs. We know that if we have to take a thermodynamic system from the initial to the final state. Isothermal Process: It is a thermodynamic process in which temperature remains constant. Figure 3: Isothermal Process Key Points W = +ve (VB > VA) W = -ve (VA > VB) dU = 0 Internal energy only depends on temperature If temperature = Constant Internal Energy = Constant. From first law of thermodynamics, Q = W + dU Q = W (dU = 0) Adiabatic Process: It is a thermodynamic process in which no heat is exchanged between the system and the surrounding. So, Q = 0. Mathematically this process is represented as: Key Points According to the 1st law of thermodynamic process Q = W + dU If Q= 0 dU = -W So, if work done is negative internal energy increases and vice versa. Isochoric Process: In isochoric process the change in volume of thermodynamic system is zero. A volume change is zero, so the work done is zero. Volume of the system = Constant Change in volume = 0 If, change in volume = 0, then work done is zero. According to the 1st law of thermodynamic law Q = W + dU If W = 0 Q = dU Isobaric Process: The pressure remains constant during this process. So, W=P(Vf-Vi) So, if volume increases, work done is positive, else negative. Key Points Pressure = Constant during this process W = P∆V So, if volume increases, work done is positive, else negative. According to thermodynamic 1st law thermodynamics Q = W + dU Q = P∆V + dU What is Enthalpy? Enthalpy is the measurement of energy in a thermodynamic system. The quantity of enthalpy equals the total heat content of a system, equivalent to the system’s internal energy plus the product of volume and pressure. Mathematically, the enthalpy (H) equals the sum of the internal energy (E) and the product of the pressure (P) and volume (V) of the system. H = E + PV What is Entropy? Entropy is a thermodynamic quantity whose value depends on the physical state or condition of a system. In other words, it is a thermodynamic function used to measure the randomness or disorder. For example, the entropy of a solid, where the particles are not free to move, is less than the entropy of a gas, where the particles will fill the container. Figure 4: Entropy Thermodynamic Potentials: Different forms of thermodynamic potentials along with their formula are tabulated below: Table 2: Different forms of thermodynamic potentials Thermodynamics Solved Problems: Calculate ΔG at 290 K for the following reaction: 2NO(g)+O2(g)→2NO2(g) Solution: Laws of Thermodynamics: Thermodynamics laws define the fundamental physical quantities like energy, temperature and entropy that characterize thermodynamic systems at thermal equilibrium. How many laws of thermodynamics are there? Zeroth law of thermodynamics First law of thermodynamics Second law of thermodynamics Third law of thermodynamic First law of thermodynamics: Energy can neither be created nor be destroyed, it can only be transferred from one form to another. Second law of thermodynamics: The entropy of any isolated system always increases. Third law of thermodynamics: The entropy of a system approaches a constant value as the temperature approaches absolute zero. Zeroth law of thermodynamics: If two thermodynamic systems are in thermal equilibrium with a third system separately, then they are in thermal equilibrium with each other. Q1: What is the importance of the laws of thermodynamics? The laws of thermodynamics define physical quantities i.e. temperature, energy & entropy that characterize thermodynamic systems at thermal equilibrium. Q2: Can energy be destroyed or lost? Energy can neither be created nor be destroyed, it can only be transferred from one form to another. Q3: Fans convert electrical energy into mechanical energy – this is explained by which law? This is explained by the First law of thermodynamics. Q4: Does the human body obey the laws of thermodynamics? Yes, the human body obeys the law of thermodynamics. When you are in a crowded room with other people, you start to feel warm, and you start to sweat. This is the body’s way to cool itself. The heat from the body is transferred to the sweat. As the sweat absorbs more heat, it evaporates from your body, becoming more disordered and transferring heat to the air, which heats the room’s air temperature. Many sweating people in a crowded room, “closed system,” will quickly heat the place. This is both the first and second laws of thermodynamics in action. No heat is lost; it is merely transferred and approaches equilibrium with maximum entropy.