Thermodynamics Solved Problems

The second law of thermodynamics states that An important implication of this law is that heat transfers energy spontaneously from higher- to lower-temperature objects, but never spontaneously in the reverse direction.This is because entropy increases for heat transfer of energy from hot to cold (Figure 12.9).possible to transfer energy by heat from a colder to hotter object.

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The gas expands to fill the chamber, but it never regroups on its own in the corner.

The random motion of the gas molecules could take them all back to the corner, but this is never observed to happen (Figure 12.10). (a) Heat transfer occurs spontaneously from hot to cold, but not from cold to hot.

Altogether, the entropy of the universe is increased by the disorder created by digging up the ore and converting it to steel. Every time a plant stores some solar energy in the form of chemical potential energy, or an updraft of warm air lifts a soaring bird, Earth experiences local decreases in entropy as it uses part of the energy transfer from the sun into deep space to do work.

There is a large total increase in entropy resulting from this massive energy transfer.

Nor does a hot, stationary automobile ever spontaneously cool off and start moving.

Another example is the expansion of a puff of gas introduced into one corner of a vacuum chamber.In the game of 52 pickup, the prankster tosses an entire deck of playing cards onto the floor, and you get to pick them up.In the process of picking up the cards, you may have noticed that the amount of work required to restore the cards to an orderly state in the deck is much greater than the amount of work required to toss the cards and create the disorder.If temperature changes during the process, then it is usually a good approximation (for small changes in temperature) to take Absolute temperature is the temperature measured in Kelvins.The Kelvin scale is an absolute temperature scale that is measured in terms of the number of degrees above absolute zero. Using temperatures from another, nonabsolute scale, such as Fahrenheit or Celsius, will give the wrong answer. If so, you have been on the receiving end of a practical joke and, in the process, learned a valuable lesson about the nature of the universe as described by the second law of thermodynamics.Third, the mixture is less orderly, or to use another term, less structured.Rather than having two masses at different temperatures and with different distributions of molecular speeds, we now have a single mass with a broad distribution of molecular speeds, the average of which yields an intermediate temperature.Energy coming from the sun can decrease the entropy of local systems on Earth—that is, is positive and greater in magnitude.In the case of the iron ore, although you made the system of the bridge and steel more structured, you did so at the expense of the universe.(Jon Sullivan, PDPhoto.org) Another way of thinking about this is that it is impossible for any process to have, as its sole result, heat transferring energy from a cooler to a hotter object.Heat cannot transfer energy spontaneously from colder to hotter, because the entropy of the overall system would decrease.

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