Thermodynamics is the study of the relationships between heat and other forms of energy. It is based on Kinetic Theory, which assumes that (i) all matter is composed of tiny particles (atoms or molecules), and (ii) these particles are in constant motion. Here are some of the things you must know. 1. Since heat is a form of energy, it is measured in Joules but can also be measured in kilocalories (kcal) with the conversion factor being 1 kcal = 4186 Joules. 2. The Celsius and Kelvin temperature scales are widely used in scientific work. One Kelvin is equal to one degree Celsius, and ΔT_{K} = ΔT_{C}. To change a Celsius temperature to Kelvin use, T_{K} = T_{C} + 273.15. 3. The Kelvin (K), is named after William Thomson, Lord Kelvin (1824 1907), British. The Celsius scale was devised by the Swedish astronomer Anders Celsius (17041744) and was based on the properties of water. 4. At absolute zero, 0.0 K, or 273.15 C, matter has a minimum thermal energy. This is regarded as the lowest temperature attainable. 5. Most solids expand when heated and contract when cooled. To measure this this effect linearly, we use the equation ΔL = α·L_{o}·ΔT , where α is the coefficient of linear expansion. 6. For volume expansion, we use the equation ΔV = β·V_{o}·ΔT , where β is the coefficient of volume expansion. 7. In an isolated system, a quantity of heat, Q , can be exchanged between substances but the total energy of the system is constant. This is known as the Law of Heat Exchange, Q_{L} = Q_{G} . 8. The quantity of heat gained or lost by any material can be calculated using the equation, Q = m·c·(T_{f} T_{i}) , with m = mass, c = specific heat capacity, and (T_{f} T_{i}) being the temperature change, ΔT. 9. The equation for phasechanging processes is Q = mL. 10. Relative humidity is defined as a percent, based on the ratio (Partial pressure of water vapor)/(Equilibrium vapor pressure of water at the existing temperature) x 100 . The Dew Point is the temperature below which the water vapor in the air condenses. 11. The conduction of heat through a bar of length L can be measured with the equation, Q = (k·A·ΔT)t/L , with k being the thermal conductivity, A is the crosssectional area, T the change in temperature, and t being the time. 12. The radiant energy, Q, emitted during a time, t, by an object whose surface area is A, and whose Kelvin temperature is T, is given by the StefanBoltzmann Law of Radiation, Q = e·σ·T^{4}·A·t . 13. The constant, σ = 5.67x10^{8} J/(s·m^{2}·K^{4}) , is known as the Stefan Boltzmann constant, and e is the emissivity, a dimensionless number characterizing the surface of the material. The emissivity lies between 0 and 1, with 0 for a nonemitting surface, and 1 for a perfect blackbody. 14. The net radiant power is the power an object emits minus the power that it absorbs. The net radiant power emitted by an object of temperature T located in an environment of temperature T_{o}, is given by the equation, P_{net} = e·σ·A(T^{4}  T_{o}^{4}). 15. The number of moles n contained in a sample is equal to the number of particles N (atoms or molecules) in the sample divided by the number of particles per mole N_{A}. We then have the equation n = N/N_{A}, where N_{A} = 6.022x10^{23} particles per mole, known as Avogadro’s Number, from Amedeo Avogadro (17761856), Turin, Italy. 16. The number of moles is also equal to the mass m of the sample (expressed in grams) divided by the mass per mole (expressed in grams per mole ). This gives us the equation n = m/(mass per mole). The mass per mole (in g/mol) of a substance has the same numerical value as the atomic or molecular mass of one of its particles (in atomic mass units). 17. The mass of a particle (in grams) can be obtained by dividing the mass per mole (in g/mol) by Avogadro's number: m_{particle} = mass per mole/N_{A}. 18. The ideal gas law relates the absolute pressure P, the volume V, the number n of moles, and the Kelvin temperature T of an ideal gas, or PV = nRT, here we have R = 8.31 J/(mol∙K), the universal gas constant. An ideal gas is one that within a range of densities, temperature, volume, and pressure have a simple relationship. 19. An alternative form of the ideal gas law is PV = NkT, where N is the number of particles and k = R/N_{A} = 1.38x10^{23} J/K , a constant named after Ludwig Boltzmann (18441906), Austria, who developed the branch of Physics known as Statistical Mechanics. 20. When a gas is kept at constant temperature, its pressure is inversely proportional to the volume. This is Boyle's Law P_{i}V_{i} = P_{f}V_{f} , named after Robert Boyle (16271691) from Ireland. 21. Also, when the pressure is kept constant, the volume is directly proportional to the temperature. This is the law of Charles and GuyLussac V_{i}/T_{i} = V_{f}/T_{f} , by Jacques Charles (17461823) and Joseph Louis GuyLussac (17781850), both from France. 22. The equation that applies here is KE_{avg} = ½ mv^{2}_{rms} = 3/2 kT, where v_{rms} is the rootmeansquare speed of the particles, derived statistically. The internal energy U of n moles of a monatomic ideal gas is U = 3/2 nRT. 23. Diffusion is the process by which solute molecules move through a solvent from an area of higher concentration to an area of lower concentration. Fick’s Law, named after Adolf Eugen Fick (18291901), Germany, states that the mass of a solute that diffuses in time through a channel of known length and crosssectional area is given by m = (D·A·ΔC)t/L . In this equation, ΔC is the solute concentration difference between the ends of the channel, and D is the diffusion constant. 24. Thermodynamics is the study of heat and how it relates to the other forms of energy (mechanical, light, sound, electric, magnetic, atomic, and nuclear). The Zeroth Law of Thermodynamics states that two systems are in thermal equilibrium if there is no net heat flow between them when they are brought into thermal contact. 25. The First Law of Thermodynamics states that the total increase in thermal energy of a system is equal to the sum of the heat added to it and the work done on it, which is given by the equation ΔU = (U_{f} U_{i}) = QW. 26. A thermal process is considered quasistatic when it occurs slowly enough that a uniform pressure and temperature exist throughout the system at all times. The work done in any kind of quasistatic process is given by the area under the pressure versus volume graph. 27. An isobaric process is one that occurs at constant pressure. The work done when a system changes at constant pressure from initial to final volume is given by the equation W = P·ΔV = P(V_{f} V_{i}). 28. An isochoric process is done at constant volume and no work is done. An isothermal process is done at constant temperature. An adiabatic process takes place without the transfer of heat. 18. When n moles of an ideal gas change quasistatically from an initial to a final volume at a constant Kelvin temperature, the work done is given by W = nRT·ln(V_{f} /V_{i}). 29. When n moles of an ideal gas change quasistatically and adiabatically from an initial to a final Kelvin temperature, the work done is according to W = 3/2 nR(T_{i} T_{f}). 30. During an adiabatic process, and in addition to the Ideal Gas Law, an ideal gas obeys the relation P_{i}V_{i}^{γ} = P_{f}V_{f}^{γ}, where γ = c_{p}/c_{v}, which is the ratio of specific heat capacities at constant pressure and constant volume. 31. The molar specific heat capacity of a substance determines how much heat is added or removed when the temperature of n moles of the substance changes. This is given by the equation Q = C·n·ΔT. 32. For a monatomic ideal gas, the molar specific heat capacities at constant pressure and constant volume are, respectively, C_{P }= 5/2 R and C_{V }= 3/2 R, where R is the Ideal Gas Constant equal to 8.31 J/(mol·K). 33. For any type of an ideal gas, the difference between C_{P }and C_{V }is R, or C_{P } C_{V }= R. 34. There are many equivalent statements for the Second Law of Thermodynamics. In terms of heat flow, the second law declares that heat flows spontaneously from a substance at higher temperature to a substance at lower temperature. 35. The second law also states that natural processes always go in a direction that increases the entropy, S, unavailable energy, or disorder, of a system. ΔS = Q – W. 36. A heat engine continuously converts thermal energy to mechanical energy and does work. The efficiency, e, of a heat engine is expressed by the equation e = (Work done)/(Input heat) = W/Q_{H}. 37. Conservation of energy requires that the input heat of magnitude Q_{H} must be equal to the work done plus the heat of magnitude Q_{C} rejected or expelled to a cold reservoir. This gives us Q_{H} = W + Q_{C}. By combining the previous two equations we arrive at the result, e = 1 – (Q_{C} / Q_{H} ). 38. A reversible process is one in which the both system and its environment can be returned to exactly the same states they were in before the process occurred. An alternate statement for the second law was stated by French engineer, Sadi Carnot (17961832). 39. Carnot’s principle states that no irreversible engine operating between two reservoirs at constant temperature can have a greater efficiency than a reversible engine operating between the same temperatures. Furthermore, all reversible engines operating between the same temperatures have the same efficiency. 40. A Carnot engine is a reversible engine in which all input heat Q_{H} originates from a hot reservoir at a single Kelvin temperature, and all rejected heat Q_{C} goes into a cold reservoir also at a single Kelvin temperature. For the Carnot engine, we have Q_{C}/Q_{H} = T_{C}/T_{H}. 41. This gives an equation for the maximum efficiency that an engine can have operating between two fixed temperatures. e_{ Carnot} = 1  T_{C}/T_{H}. 42. A heat pump, air conditioner, or refrigerator uses mechanical energy to transfer heat from an area of lower to higher temperature. These are governed by the Law of Conservation of Energy with Q_{H} = W + Q_{C}. 43. The coefficient of performance of a refrigerator or air conditioner is given by the equation Coefficient of performance = Q_{C} /W. For the heat pump we have a similar relationship, Coefficient of performance = Q_{H}/W. 44. The change in entropy, ΔS, for a process in which heat enters or leaves a system reversibly at a constant Kelvin temperature is ΔS = (Q/T)_{R}, where the subscript R stands for "reversible." 45. In terms of entropy, the second law states that the total entropy of the universe does not change when a reversible process occurs (ΔS_{universe} = 0 J/K), and increases when an irreversible process occurs (ΔS > 0 J/K). 46. Irreversible processes cause energy to be made unavailable for the performance of work. This energy is given by W_{unavailable} = T_{o}·ΔS_{universe} where ΔS_{universe} is the total entropy change in the universe and T_{o} is the Kelvin temperature of the coldest reservoir into which heat can be rejected. 47. And still, we need these steps to solve any problem in Physics: (i) read the problem and identify the given variables (ii) determine what you are asked to solve for (iii) find the correct equation to use (iv) use Algebra, Trigonometry, and/or Calculus to isolate the unknown (v) substitutein the given information and simplify. Click Thermal Energy to view the PowerPoint. End of Introduction to Thermodynamics. Click HERE to continue. For a Sample Problem Set #1 on Thermodynamics. Click HERE. For a Sample Problem Set #2 on Thermodynamics. Click HERE. For REVIEW Problem Set on Thermodynamics. Click HERE. For the Heat of Fusion Lab Handout. Click HERE. For the Lab Abstract template. Click HERE.
 

