## knocknock 2 years ago If mass energy equivalence is taken into account, when water is cooled to form ice, the mass of water should: A) Increase B) Decrease C) Not change D) First increase then decrease

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1. SerikMB

Probably, the answer is C. Because when the material changes it's phase, it changes it's density, so only volume is affected.

2. knocknock

Well, the answer is A and the explanation says "According to mass energy equivalence, mass and energy remain conserved. so, when water is cooled to form ice it loses energy. So, change in energy increases the mass of water." But I can't understand it because it's a little vague. I think that mass should decrease since \[\Delta E=(\Delta M) c^2\] Energy is being taken out of water, consequently some mass of the water is converted to this energy lost. So net mass decreases. Am I correct?

3. yrelhan4

@Mashy

4. shivaniits

hmm..interesting for mass energy equivalence it should increase as energy gets converted to mass but it is not that we should that consider the fact that the energy still lies with in the system may be it gets lost to the surroundings...but if we do not talk about anything else but the system i mean not considering any losses then yup acc. to mass energy equivalence it should increase but we can't ignore the basic law here: regardless of anything how can total mass of a system be changed alright you will say that nuclear reactions are such example of this thing but don't you think nuclear reactors bombard atoms with high energy so that the nuclear force too get involved in the reaction but while cooling the water we are not giving such amount of energy.. plus i think this mass energy equivalence concept is really misunderstood sometimes..!! http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ it is EINSTEIN work on mass energy equivalence and he raised this mass energy equivalence concept from do inertia of a body is dependent on its energy content ..!! i guess it would clear out your doubts.. do correct me if am wrong..:)

5. Mashy

what nonsense?! the answer is C.. mass does not change like.. lol! @knockknock.. it loses its energy to surroundings thats all!!.. whatever amount of energy it has lost is been given out to the surroundings.. mass energy only comes into play if you can unlock the energy of the nucleus and that is only when you go for nuclear reactions!..

6. shivaniits

yup it could only be possible in case of nuclear reactors where the direct conversion could be viewed but the inertia thing is possessed by everything and it is the factor that made einstein develop the strong concept of mass energy equivalence..but here as far i could say the cooling water system doesn't possess much energy..!!

7. Mashy

i thought it was the fact that nothing could beat the speed of light was what made einstien come up with the concept.. and the fact that maxwell had hypothized that electromagnetic waves will always keep going away from you at speed of light no matter what you do.. !

8. shivaniits

hmm..thats from where the mathematical derivation and understanding of mass-energy equivalence concept was established..but it not only prepared mathematical base for mass energy equivalence but also for special theory of relativity..!! you can check it out here: its einstein's work http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ published as Does the inertia of a body depend upon its energy-content?

9. gleem

From Einstein's mass energy equivalence we know moving objects are more massive than resting objects. Warm bodies are made up of vibrating molecules ie. moving bodies. When cooling occurs the molecules are slowed. Thus don't we expect the total observed mass to decrease as cooling continues.

10. Mashy

omg.. but do we have to consider that.. cause if we consider that. then mass always keeps fluctuating :P.. m pretty sure taht ONLY comes into play when we talk about relativity..!!

11. gleem

If this question is a relativity context it is like asking how much heavier we get when we run: not much. In a thermodynamic context would this energy change be somehow included in the internal energy?

12. Mashy

no.. we will definitely not consider that in thermodynamics :P!..