Ideal Gas and Laws of Thermodynamics, Lecture notes of Physics

Download Ideal Gas and Laws of Thermodynamics and more Lecture notes Physics in PDF only on Docsity! Notre Dame of Marbel University Integrated Basic Education Department SENIOR HIGH SCHOOL General Physics 1 “ij: NDMU = IBED SHS | Lesson 14 ee 6° General Physics 1 Ideal Gas and Laws of Thermodynamics Tomarong, J. A., MASCEd Properties of Ideal Gases: 4. The collisions exhibited by gas particles are completely elastic; when two molecules collide, total kinetic energy is conserved. 5. The average kinetic energy of gas molecules is directly proportional to absolute temperature only; this implies that all molecular motion ceases if the temperature is reduced to absolute zero. eS pane” % ‘ NDMU =IBED SHS | Lesson 14 re Ideal Gas What are the assumptions of the Kinetic Molecular Theory? Tomarong, J. A.. MASCEd Gas Laws: 1. Boyle’s Law “At constant temperature, pressure is inversely proportional to volume.” 𝑷𝟏𝑽𝟏 = 𝑷𝟐𝑽𝟐 Gas Laws: 4. Combined Gas Law – combines the three gas laws: Boyle's Law, Charles' Law, and Gay- Lussac's Law “The ratio of the product of pressure and volume, and the absolute temperature of a gas equals a constant.” 𝑷𝟏𝑽𝟏 𝑻𝟏 = 𝑷𝟐𝑽𝟐 𝑻𝟐 Gas Laws: 5. Ideal Gas Law: 𝑷𝑽 = 𝒏𝑹𝑻 𝑷𝑽 = 𝑵𝒌𝑩𝑻 where: P is pressure in pascals; V is volume in cubic meters; n is the number of moles; R is the universal gas constant (R = 8.314 J/mol K); T is temperature in kelvin; N is the total number of molecules; and kB is the Boltzmann constant (kB = 1.38 x 10- 23 J/K); N = nNA, where NA is the Avogadro’s number equal to 6.02 x 1023 particles per mole. First Law of Thermodynamics Thermodynamics – concerned with heat and its transformation to mechanical energy; literally means “moving or evolving heat” Sadi Carnot – father of Thermodynamics Reversible process – system and its surroundings can be returned to their initial state before undergoing a process Irreversible process – system and its surroundings cannot return to their initial state First Law of Thermodynamics “When heat is added to a system, some of it remains in the system, increasing its internal energy, while the rest leaves the system as the system does work.” 𝑸 = ∆𝑼 +𝑾 where: Q is the heat added to the system; ΔU is the change in internal energy; and W is the work done by the system +Q – heat added to the system +W – work done by the system -Q – heat removed from the system -W – work done on the system Internal Energy – sum of the kinetic and potential energies possessed by the molecules of an object due to their motions and positions relative to each other ∆𝑼 = 𝒏𝑪𝑽∆𝑻 Thermodynamic Processes and PV Diagrams Thermodynamic Process – change from an initial state to a final state of a system that usually involves a change in its pressure, volume, or temperature 1. Isochoric process – constant volume process (ΔV = V2 – V1 = 0); no work done (ΔW = 0) 𝑸 = ∆𝑼 2. Isobaric process – constant pressure process (ΔP = 0) 𝑾 = 𝑷(𝑽𝟐 − 𝑽𝟏) 𝑷𝟏𝑽𝟏 𝜸 = 𝑷𝟐𝑽𝟐 𝜸 𝑻𝟏𝑽𝟏 𝜸−𝟏 = 𝑻𝟐𝑽𝟐 𝜸−𝟏 𝑷𝟏 𝜸−𝟏 𝑻𝟏 𝜸 = 𝑷𝟐 𝜸−𝟏 𝑻𝟐 𝜸 where: 𝜸 = 𝑪𝑷 𝑪𝑽 is the ratio of the specific heat capacity of an ideal gas at constant pressure to the specific heat capacity of an ideal gas at constant volume Thermody namic Processes Constant Thermodynamic Variable Change in the Internal Energy Heat Work Done Example Isochoric Volume ΔU = ΔQ Heat added to the system is used to increase the internal energy. ΔW = 0 Heating of a closed rigid container Isobaric Pressure ΔU = ΔQ – PΔV Heat added to the system is used to increase the internal energy and do work. W = PΔV = P(V2 – V1) Boiling, heating water in an open container Expansion of gas in a cylinder containing a piston moving freely Isothermal Temperature ΔU = 0 ΔQ = W Energy added to the system as heat is used to do work. Change of phase such as freezing and melting Adiabatic No heat transfer ΔU = –W ΔQ = 0 Work done on the system increases the internal energy of the system. Opening a bottle of carbonated drink quickly The Second Law of Thermodynamics Second Law of Thermodynamics – limits the amount of work a heat engine can do for a certain amount of heat 1. Kelvin-Planck Statement “No heat engine can completely convert heat energy to work. In other words, there is no 100 percent heat engine.” Heat Engines – devices that convert thermal energy to mechanical energy Working substance – substance inside the heat engine that undergoes cooling and/or heating, compression and/or expansion, and sometimes phase change 1.Heat (QH) is supplied to the engine by an external source called hot reservoir or heat source; 2.Part of the heat is used to do work on an object; 3.The rest of the heat (QC) is released at a temperature lower than the input temperature to an external place called the cold reservoir or the heat sink. Efficiency of Heat Engine Efficiency (ε) – how much of the input is converted to work 𝜺 = 𝟏 − 𝑸𝑪 𝑸𝑯 × 𝟏𝟎𝟎% where: ε is the efficiency of an heat engine; QC is the heat released to the cold reservoir; QH is heat supplied by the heat engine Change in Entropy (ΔS) – heat (QH) added or released during the process divided by the temperature (T) ∆𝑺 = 𝑸 𝑻 Entropy when heat is added or removed from a solid or liquid: ∆𝑺 = 𝒎𝒄 𝐥𝐧 𝑻𝟐 𝑻𝟏 SI Unit: J/K The entropy statement of the second law may be written as: ΔS of universe = 0 for reversible processes; and ΔS of universe > 0 for irreversible processes Alternative Entropy Statement of Second Law: “All natural or spontaneous processes tend toward a state of greater disorder.” ∆𝑺 ≥ 𝟎 How can we lessen the impact of climate change and global warming?