Thermodynamics Notes - Temperature, Internal Energy, and Laws - PDF

Week 2 Thermodynamic System Temperature Internal energy Thermal Equilibrium 0th Law of Thermodynamics 1st Law of Thermodynamics 2nd Law Ways of heating Global warming (cooling) Statistically significant changes in Global mean...

Week 2 Thermodynamic System Temperature Internal energy Thermal Equilibrium 0th Law of Thermodynamics 1st Law of Thermodynamics 2nd Law Ways of heating Global warming (cooling) Statistically significant changes in Global mean surface temperature T “Current” Global warming T GMST has increased ~0.9 degrees over the last century  Temperature Changes, Global Heat, Heat Transfer Warming Thermodynamics  Mechanics vs Thermodynamics Mechanics: Thermodynamics: 1st Law: no interaction => equilibrium 0th Law: no interaction => equilibrium Mechanical Equilibrium: v=const Thermal Equilibrium: T=const E=const U=const The only one way to change ME: work The main way to change TE: heat Mechanics: Thermal Physics: set of laws to describe transitions from set of laws to describe transitions from one one mechanical Equilibrium to another: Thermal Equilibrium State to another: 2nd Law 1st Law, …. Thermodynamic System and Boundary of system Gas Liquid Solid Plasma or their combination A thermodynamic system is a part of the physical universe (should includes large number of particles) A boundary is a closed surface surrounding a system Everything external to the system is the surroundings (environment) Solid: particles are arranged in a definite pattern. Solids Liquid: no definite pattern, have a have both a definite shape definite volume but assume the and a definite volume shape of their containers Gas: particles travel independently in straight- Plasma: composed of line paths. Gases assume electrons and positive ions at the shape and volume of very high temperatures. their container. Temperature - one of the most important quantity in Thermodynamics Easy to measure Operational definition- T is what we measure with thermometer Based on thermal expansion  Temperature Scales Thermometers can be calibrated by placing them in thermal contact with some object that remains at constant temperature Celsius scale (1742- Anders Celsius): mixture of ice and water water and steam in thermal equilibrium in thermal equilibrium Freezing point ice–water mixture defined as 0°C Boiling point water–steam as 100°C Distance between these 2 points divided into 100 equal segments Fahrenheit scale: (most common scale used in the U.S.), 1724 (Daniel Fahrenheit) – Employs a smaller degree than Celsius scale – Uses a different zero of temperature than Celsius scale Temperature of the freezing point of water is set at 32°F Temperature of the boiling point of water is set at 212°F 180 divisions between these 2 points Conversion between Celsius (TC) and Fahrenheit (TF) temperatures: 9 TF = TC + 32 o 5 In defining Celsius and Fahrenheit scales we used water (freezing and boiling points) and the fact of “thermal expansion” 0 is arbitrary chosen (doesn’t have any physical meaning) so both Celsius and Fahrenheit scales are not fundamental 9 TF = TC + 32 o 5  Kelvin Temperature Scale (absolute temperature), 1848 Named for British physicist (William Thomson) Lord Kelvin (1824–1907) Units same as those on Celsius scale, but zero point is shifted so that 0 K = –273.15°C T K = T C + 273. 15 This is not a relative scale with an arbitrary zero point, but has as its lowest point absolute zero – the lowest possible temperature.  Gas Thermometer 3 data sets (trials) for 3 different amount of gas in the bulb (at 0o and 100o C) P T In each case, regardless of the gas amount (and gas used), the curves extrapolate to the same temperature (absolute zero) at zero pressure Gases liquefy and solidify at very low temperatures, so we can’t actually observe this zero-pressure condition The absolute-zero reference point forms basis of Kelvin temperature scale Temperatures Range  Internal Energy The internal energy of a substance is the total kinetic and potential energy of the molecules of a substance. U = kinetic + potential U is less than total energy (+mc2, motion as whole system (translational and rotation) No apparent energy on Macroscopic view How energy from heating or work is stored? Q, W U = kinetic + potential Sometimes all energy goes (stored) into kinetic energy: KE = ½ mv2 Q, W KE = ½ mv2 =3/2 kT k-Boltzmann’s constant Temperature is measure of the average kinetic energy (of translational motion) of atoms or molecules! Sometimes all Energy (stored) into potential energy (chemical bonding) No temperature change during phase transformations! Energy (heat) taken or released is called latent heat Thermal Equilibrium 0th Law of Thermodynamics 1st Law of Thermodynamics 2nd Law Ways of heating Thermal Equilibrium Experimental fact: When you put two objects (systems) in thermal contact and wait long enough, they tend to come to the same temperature. TAf TBf TAi TBi Tai> or U2=Q, Internal Energy of object 2 is increased by Q (object heated) U = Q First Law of Thermodynamics (not general form)  First Law of Thermodynamics (general form) the internal energy of a system can be U changed by heating/cooling or doing work. U = Q + W Q – energy flow between a system and its environment due to T across a boundary (heating (Q > 0) or cooling (Q < 0), we will call it Heat W - any other kind of energy transfer across boundary - Work The internal energy of a substance is the total kinetic and potential energy of the molecules of a substance. U = kinetic + potential 2nd Law: Q (heat) T1 T2 T1>T2 Naturally (in isolated system), energy (net energy) flows from higher temperature to low temperature objects One of the consequences (or foundations) of 2nd Law  Ways of Heating Three mechanisms for heat transfer due to a temperature difference 1. Conduction 2. Convection 3. Radiation  Conduction (gases) Temperature is measure of the average kinetic energy (of translational motion) of atoms or molecules! ½ mv2 =3/2 kT Conduction (solids (liquids))  Energy transfer through the bulk Convection motion of hot material Examples – heater – gas furnace (forced) Natural convection mechanism - “hot air rises”  Few words about quantum world Q Q 3 degrees of freedom 3 degrees of freedom (translational)+ (translational) Some vibration+ Some rotational+ Q is split equally Q is split equally between all (3) degrees of freedom between all degrees of freedom  Few words about quantum world (let us consider two atomic gas) At low temperatures, translational energy Q of molecules 3/2 (kT) is smaller then energy levels of rotational and vibrational motions, so all Q stores in translations and T is rising faster At higher T some portions of Q goes to rotate then later to vibrate molecules, so less and less Translation Rotation Vibration Portion of Q goes into translation 1 atom T increase T 1 atom Two atoms T Two atoms Q Q Quantum view Mechanistic view