# Homework Help: Theory Thermodynamics 2º Law

1. May 23, 2015

### Awanerv

Hi

My problem is

1. The problem statement, all variables and given/known data

To raise 1°C the temperature of 1 liter of water, we spend 1 kcal. Therefore, cooling of 1°C 1 liter of water, it should be possible to extract 1 kcal of energy. Based on this principle, a ship could be propelled by the energy and simultaneously cool their cargo: the ocean would be a virtually inexhaustible reservoir of energy. Explain why this is not working.

2. Relevant equations
N/A

3. The attempt at a solution

I think is not possible because the neighborhood is very big ( ocean ) and the temperature of water is constant is impossible to extract energy from ocean and cool the water -1° C .

2. May 23, 2015

### BvU

Hello Awanerv, welcome to PF !

If I understand the exercise properly, I think they want to use warmth from either the cargo or from the ocean ?
Did you skip a word when typing in the problem statement ?

3. May 23, 2015

### Awanerv

No

I really dont know , how to answer this question properly

Thanks BvU

4. May 23, 2015

### BvU

Well, you have the title of this thread ! What did you learn in the section on this topic where this question is asked ?

5. May 23, 2015

### Awanerv

Hi BvU

I try to find the source of this question but not succeed

The question is from my class ( thermodynamic )

I copy the question from the whiteboard from my teacher

I was think the question is formulated by the teacher

anyway thanks for help

6. May 23, 2015

### BvU

You have to do some research into this 2nd law, then. Try to figure out why you can't get work (energy) out of a process that brings heat from a cold place to a warm place. (refrigerators use electric power to do their cooling).

7. May 23, 2015

### insightful

8. May 24, 2015

### BvU

Dear Awa,

I suppose the exercise statement you gave us is a wordly translation, and I still can't distinguish between two thinkable options:

1. they want you to think why you can't extract energy from the cargo (a potentially useful thing) and use that energy to propel the ship.
2. they want you to think why you can't extract energy from the ocean and use that energy to propel the ship and also to cool the carge. Double useful.

All this in the context of apparent limitations forced by the second law.
So again, I urge you to find out about this second law and what it means for imagined processes like the one described in this exercise.
To begin with, you could state the second law in your own words. And it would be really nice if we can work towards an equation (yes! N/A under 2. was a missed opportunity !) that relates work done to changes in heat.

At this point a comment that may be very useful in PF and also in other comparable situations: Telling that you didn't succeed doesn't improve the situation. There's nothing wrong with not succeeeding (it is far better than not having tried!), but the information doesn't help people like me to provide useful assistance. Better to tell us what you did find. And what you already do know is also important, otherwise we can't use meaningful wording while assisting.

@insightful: At this stage searching around for complicated processes is not helping Awanerv to understand the concepts of the second law.

Last edited: May 24, 2015
9. May 24, 2015

### Awanerv

Hi BvU

Thanks for all reply

I will try to answer with my own word plus second law of thermodynamic

Best Regards