Using modern sign convention, PV work…

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Presentation transcript:

Using modern sign convention, PV work… QUESTION: Calculate the work associated with the compression of a 3.00 L sample of gas to half its original volume, due to an external pressure of 2.00 atm. A. 0.303 kJ, B. 0.667 J, C. 1.50 J, D. 3.00 kJ w = - Pex dV = - Pex V = - (2.00 atm) (1.50 L – 3.00 L) = - (2.00 atm) (-1.50 L) = + 3.00 L atm  303 J, or 0.303 kJ NOTE: 1 L atm = 101.325 J, or 0.101325 kJ Calculate the work associated with the compression of a 3.00 Liter sample of gas to half its original volume, due to an external pressure of 2.00 atmospheres. PAUSE Work due to expansion or compression of an object is called “pressure volume work”,… or PV work Using modern sign convention, PV work… CLICK is calculated by taking the negative of integral of the external pressure with respect to volume. CLICK If the external pressure is constant while the system’s volume is changing, then the formula for PV work simplifies to … negative of external pressure, times change in volume Let’s plug in the numbers, …. …. External pressure is 2.00 atmospheres …. Change in volume is given by the final volume CALLOUT “half of 3.00 L” pointing to 1.50 L 1.50 liters is one-half of 3.00 liters. HIGHLIGHT 1.50 L …. Minus the initial volume HIGHLIGHT 3.00 L Note that the problem says that the final volume is half of the original volume. Therefore, our change in volume is NEGATIVE 1.50 L And w is equal to POSITIVE 3.00 liter atmospheres. We need to convert this value to Joules or kilojoules since these are the units given in the choices. One liter atmosphere is equivalent to 101.352 joules or 0.101325 kilojoules. Therefore, 3.00 liter atmospheres is equivalent to 303 joules, or 0.303 kilojoules. The correct answer is choice A. CLICK PAUSE END RECORDING

Video ID: 8-6-2 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Assisted by Johuan Gasery In partial fulfillment of the requirements for CHEM 481, Fall 2008.