Presentation is loading. Please wait.

Presentation is loading. Please wait.

MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010.

Similar presentations


Presentation on theme: "MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010."— Presentation transcript:

1 MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010

2 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

3 MFS Work Done by the system

4 MFS Work Done by the system Where: W = work done by the system [J] p = pressure [p a ] dV = differential volume [m 3 ] V 1 & V 2 = initial and final volume [m 3 ] dS F A

5 MFS Work Done by the system Where: W = work done by the system p = pressure dV = differential volume V 1 & V 2 = initial and final volume V1V1 V2V2 pV-diagram 0 p V

6 MFS Work Done by the system Signs of work done

7 MFS Work Done by the system If the pressure is constant during thermodynamic process

8 MFS Problem

9 MFS Work Done by the system Paths Between Thermodynamics States

10 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

11 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

12 MFS The First Law of Thermodynamics

13 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?

14 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)

15 MFS Kinds of Thermodynamic Process

16 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.

17 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

18 MFS Type of Gas GasC V (J/mol.K) C p (J/mol.K) C p -C V (J/mol.K) (J/mol.K) MonatomicHe Ar DiatomicH2H N2N O2O CO PolyatomicCO SO H2SH2S Molar Heat Capacities of Gases

19 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

20 MFS Example. In an experiment to simulate conditions within an automobile engine, 645J of heat is transferred to 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

21 MFS Adiabatic Process for an Ideal Gas No heat transfer, Q = 0

22 MFS Adiabatic Process for an Ideal Gas Adiabatic process, ideal gas


Download ppt "MFS First Law of Thermodynamics Created by: Marlon Flores Sacedon Physics section, DMPS June 2010."

Similar presentations


Ads by Google