Presentation on theme: "MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010."— Presentation transcript:
MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010
MFS The First Law of Thermodynamics Thermodynamic system is a system that can interact (and exchange energy) with its surroundings, or environment, in at least two ways, one of which is heat transfer. Thermodynamic process is a process in which there are changes in the state thermodynamic system. Work Done during volume changes
MFS Work Done by the system Paths Between Thermodynamics States
MFS Internal Energy (U) Internal Energy of a system is the sum of kinetic energies of all of its constituent particles, plus the sum of all the potential energies of interaction among these particles. Where: = change in internal energy U 1 = initial internal energy U 2 = final internal energy
MFS System Surroundings (environment) The First Law of Thermodynamics = Q-W = +50 J System Surroundings (environment) = Q-W = -50 J System Surroundings (environment) Q = 150JW = 150J = Q-W = 0 Q = -150J W = -100J Where: = change in internal energy (J) W = work done (J) Q = heat quantity (J) Q = 150JW = 100J
MFS The First Law of Thermodynamics Ex. A gas in a cylinder is held at a constant pressure of 2.30x10 5 Pa and is cooled and compressed from 1.70 m 3 to 1.20 m 3. The internal energy of the gas decreases by 1.40x10 5 J. a) Find the work done by the gas. b) Find the absolute value of the heat flow into or out of the gas, and state the direction of heat flow. c) Does it matter whether or not the gas is ideal? J, b) 2.55x10 5 J, out of gas, c) no (Ans. a) -1.15x10 5 Ex. A gas in a cylinder is held at a constant pressure of 2.30 x 10 5 Pa and is cooled and compressed from 1.70 m 3 to 1.20 m 3. The internal energy of the gas decreases by 1.40 x 10 5 J. a) Find the work done by the gas, b) Find the absolute value |Q| of the heat flow into or out of the gas, and state the direction of heat flow, c) Does it matter whether or not the gas if ideal? Why or who not?
MFS Kinds of Thermodynamic Process 1. Adiabatic Process (pronounced ay-dee-ah-bat-ic) is defined as one with no heat transfer into or out of a system: Q = 0. (adiabatic process) 2. Isochoric Process (pronounced eye-so-kor-ic) is a constant- volume process. When the volume of thermodynamic system is constant W=0. (isochoric process) 3. Isobaric Process (pronounced eye-so-bear-ic) is a constant – pressure process. (Isobaric process) 4. Isothermal Process (pronounced eye-so-bear-ic) is a constant –temperature process. (Isothermal process)
MFS Internal Energy of an Ideal Gas Property of Ideal Gas: The internal energy of an ideal gas depends only on its temperature, and not on its pressure and volume.
MFS Heat Capacity of an Ideal Gas Molar heat capacity at constant volume (C V ) Molar heat capacity at constant pressure (C p ) (First Law) At constant volume (from First Law) (because dQ=dU) or At constant pressure ( from pV=nRT ) (Molar heat capacities of an ideal gas) (ratio of heat capacities) Where: C p = molar specific at constant pressure (J/mol.K) C V = molar specific at constant volume (J/mol.K) R = ideal gas constant initial and final volume
MFS Type of Gas GasC V (J/mol.K) C p (J/mol.K) C p -C V (J/mol.K) (J/mol.K) MonatomicHe12.4720.788.311.67 Ar12.4720.788.311.67 DiatomicH2H2 20.4228.748.321.41 N2N2 20.7629.078.311.40 O2O2 20.8529.178.311.40 CO20.8529.168.311.40 PolyatomicCO 2 28.4636.948.481.30 SO 2 31.3940.378.981.29 H2SH2S25.9534.608.651.33 Molar Heat Capacities of Gases
MFS Heat Capacity of an Ideal Gas Molar heat capacities for Monatomic ideal gas Molar heat capacities for Diatomic ideal gas Molar heat capacities for Polyatomic ideal gas
MFS Example. In an experiment to simulate conditions within an automobile engine, 645J of heat is transferred to 0.185 mol of air-conditioned within a cylinder of volume 40.0cm 3. Initially the nitrogen is at a pressure of 3.00x10 6 Pa and a temperature of 780K. a) If the volume of the cylinder is held fixed, what is the final temperature of the air? Assume that the air is essentially nitrogen gas, use the Table. Draw a pV-diagram for this process. b) Find the final temperature of the air if the pressure remains constant. Draw a pV- diagram for this process
MFS Adiabatic Process for an Ideal Gas No heat transfer, Q = 0
MFS Adiabatic Process for an Ideal Gas Adiabatic process, ideal gas