Consider the energy balance equation for a closed system: deltaU+deltaE k +delta
ID: 1330877 • Letter: C
Question
Consider the energy balance equation for a closed system: deltaU+deltaEk +deltaEp=Q-W.
Given the scenarios and systems described below,sort the energy balance equation terms according to if they are less than zero,equal to zero, or greater than zero.
Scenario 1: You put a jar of pickles,intially at room temperature, into the refirgerator, and the jar contents cool to 38*F. Consider the system to be the jar contents, and assume that the shelf in the refrigerator is at the same height as the counter which the jar initially rested.
Scenario 2: The same pickle jar falls off the shelf and is about to hit the floor. Consider the pickle jar to be the system, and for there to be negible heat transfer and temperature change during this process.
Scenario 3:On a cold day,water rests in a small crack in an asphalt road. As night falls, ice freezes, expands, and causes the crack to grow into a pothole. Consider the system to be water.
Explanation / Answer
Scenario 1:
As the height is same, change in potential energy is same => deltaEp = 0
No Velocity => deltaEk = 0
as the system cooled => internal energy decreases (as work done is zero and Q < 0)
=> deltaEk < 0
W = 0
Scenario 2:
As the heat transfer is negligible Q = 0
As the temperature change of the system during the process is negligible
deltaU = 0
As the jar fell from high potential to low potential (potential Energy decreases)
deltaEp < 0
As the jar fell from rest and it acquires some velocity before hitting the floor (Kinetic Energy Increases)
deltaEk > 0
Scenario 3:
As there is no change in the positions and velocity of the system.
potential and kinetic energies remain same
=> deltaEk = 0 and deltaEp = 0
As heat is released by the system Q < 0 (As the system cooled) and work is done by the system W > 0 (In causing the crack to grow into a pothole)
=> deltaU < 0 (Internal Energy decreased)