Conservation of Energy vs Conservation of Mass

[Guest]

 For fun, I’m re-reading Plutonium: A History Of The World’s Most Dangerous Element. By Jeremy Bernstein (Cornell University Press, 2007). 

I want to confirm a “big idea”...

1. In non-nuclear chemistry (that I teach in the high school science classroom, junior grades), the law of conservation of mass holds true.  It’s the basis of balancing chemical reactions.

2. The moment I start bombarding neutrons at nuclei, the above law fails.  The Law Of Conservation of Energy then takes over. It follows Einstein’s famous equation E = mc2.

 

Yes? No? Uh...

 

Sincerely, PrometheanCat.

[MedievalMatt]

8 minutes ago, PrometheanCat2 said:

 For fun, I’m re-reading Plutonium: A History Of The World’s Most Dangerous Element. By Jeremy Bernstein (Cornell University Press, 2007). 

I want to confirm a “big idea”...

1. In non-nuclear chemistry (that I teach in the high school science classroom, junior grades), the law of conservation of mass holds true.  It’s the basis of balancing chemical reactions.

2. The moment I start bombarding neutrons at nuclei, the above law fails.  The Law Of Conservation of Energy then takes over. It follows Einstein’s famous equation E = mc2.

 

Yes? No? Uh...

 

Sincerely, PrometheanCat.

I thought it was matter.  Conservation of matter.  it can never be created nor destroyed.  only changing forms.  Mass is variable.  Maybe im an idiot?

[PhantomJaguarr]

1 hour ago, PrometheanCat2 said:

the above law fails.

This part is confusing. I don't understand how it fails? If it's just converted to another form...

[Dissitesuxba11s]

1 hour ago, MedievalMatt said:

I thought it was matter.  Conservation of matter.  it can never be created nor destroyed.  only changing forms.  Mass is variable.  Maybe im an idiot?

Correct and not correct; it is conservation of mass. Mass is the amount of matter in an object; weight is what's variable. 

 

When you bombard a nuclei with neutrons, they split into different particles with separate atomic weights but smaller combined mass (this is why it "fails"). Some of that mass is converted into energy during separation during a process called nuclear fission.

 

Just trying to remember what I learned in school. Please correct me if I'm wrong.

Edited November 24, 2017 by Dissitesuxba11s
Worded better

[Guest]

58 minutes ago, Dissitesuxba11s said:

Correct and not correct; it is conservation of mass. Mass is the amount of matter in an object; weight is what's variable. 

 

When you bombard a nuclei with neutrons, they split into different particles with separate atomic weights but smaller combined mass (this is why it "fails"). Some of that mass is converted into energy during separation during a process called nuclear fission.

 

Just trying to remember what I learned in school. Please correct me if I'm wrong.

Thanks for the insight, eh.  I looked at my “fail” usage... It reminds me again how classical chemistry.... nuclear chemistry... and electrochemistry have nuanced differences.

 

Thanks for all the responses. I’m glad I’m attempting this reading again. Its comprehension remained elusive for me.

 

[Guest]

1 hour ago, WhiteJaguar77 said:

This part is confusing. I don't understand how it fails? If it's just converted to another form...

As I’m reading about the history of nuclear chemistry, the author’s attempting to recreate the problems our forefathers (and foremothers) had to tackle.  Example: slower moving neutrons affect nuclei more than fast moving nuclei. Fun! Good for my brain...

[pyrojoe34]

Yea that's about right. But keep in mind they do split into two atoms of smaller mass, the mass is still (mostly) conserved in the neutrons that are released. However, about 0.1% of the mass is converted to energy so you do end up with a little less mass.

 

Example of fission reaction:

Uranium 235 gets hit with (and absorbs) a neutron to form Uranium 236. This splits into Krypton 92 and Barium 141 (which add to 233), AND releases 3 neutrons (as well as some gamma photons and a ton on energy) which makes the total mass of the products 236. You can see that nothing is lost in the reaction, only rearranged.

[captain_to_fire]

2 hours ago, PrometheanCat2 said:

The moment I start bombarding neutrons at nuclei, the above law fails.  The Law Of Conservation of Energy then takes over. It follows Einstein’s famous equation E = mc2.

I’m thinking, if a kilogram of Uranium-235 was bombarded with neutrons, the U-235 nuclei split into lighter elements. If we take into account the energy released and the weight of the lighter elements released, then it still follows the law of mass conservation, I think. Maybe @Godlygamer23 can correct me on this. 

 

2 hours ago, PrometheanCat2 said:

In non-nuclear chemistry (that I teach in the high school science classroom, junior grades), the law of conservation of mass holds true.  It’s the basis of balancing chemical reactions.

You’re correct about this. Whether it’s burning fossil fuels or acid rain eroding statues or a redox reaction, no mass is created nor destroyed. 

[Guest]

9 minutes ago, pyrojoe34 said:

No. Although they do split into two atoms of smaller mass, the mass is still conserved in the neutrons that are released.

 

Example:

Uranium 235 gets hit with (and absorbs) a neutron to form Uranium 236. This splits into Krypton 92 and Barium 141 (which add to 233), AND releases 3 neutrons (as well as some gamma photons and a ton on energy) which makes the total mass 236. You can see that nothing is lost in the reaction, only rearranged.

Ah! Thank you, @pyrojoe34. So, the Law of Conservation of Mass doesn’t contradict the Law of Conservation of Energy.... even at the nuclear-level.

 

It gets frustrating in my classroom... how dogmatically I teach the Law of Conservation of Mass... without acknowledging nuclear chemistry.  And DON’T even get me started about teaching optics in grade 10 science.  My definition of “light” is idiotic.  And then I try describing the electromagnetic spectrum.  “Light is a wave”. Okaaaaaaaayyyyy.....

 

I’ve had grade 11-12 physics teachers go pale when I suggest teaching photons in the junior grades.  Heh heh.

 

Edited November 24, 2017 by Guest
Ranting and raving...

[pyrojoe34]

4 minutes ago, PrometheanCat2 said:

Ah! Thank you, @pyrojoe34. So, the Law of Conservation of Mass doesn’t contradict the Law of Conservation of Energy.... even at the nuclear-level.

 

Sorry I just modified the post, I wrote it too quickly and screwed up. A small amount of mass (0.1%) IS converted energy in a fission reaction (kinetic energy and photons). However, the energy released is equal to the mass lost so it is still conserved in the reaction.

[Guest]

6 minutes ago, pyrojoe34 said:

Sorry I just modified the post, I wrote it too quickly and screwed up. A small amount of mass (0.1%) IS converted energy in a fission reaction (kinetic energy and photons). However, the energy released is equal to the mass lost so it is still conserved in the reaction.

Ah, photons.  What the hell are these “units”. Particles? A wave of xxx? After this book, I’m going to pick up Einstein’s biography (that attempts to outline the photon-effect [?] and relativity).  Give it another go. Perhaps I’ll grok it for more than about 5 minutes.

[pyrojoe34]

16 minutes ago, PrometheanCat2 said:

Ah, photons.  What the hell are these “units”. Particles? A wave of xxx? After this book, I’m going to pick up Einstein’s biography (that attempts to outline the photon-effect [?] and relativity).  Give it another go. Perhaps I’ll grok it for more than about 5 minutes.

Photons are what EM waves are made of (visible light, microwaves, radio waves, UV, IR, etc). (light is both a wave and a particle, look at the double-slit experiment for more. The wave-particle duality and quantum properties of light are counter-intuitive but amazing to learn about.) They are considered "massless" (for practical purposes) so they don't factor into the equation (their energy does though). The neutrons and protons (together known as nucleons) have mass (both equal ~1) and so do electrons and positrons (both ~0.05). The "large" particles are made up of smaller subatomic particles like bosons/leptons/quarks which give them properties (like charge, nuclear force, mass, etc).

 

Anyway, I'm not a physicist (just a biomedical scientist) so at this point things get way beyond my knowledge. It's really fun to learn about though, keep reading up, the world of particle physics is a fascinating rabbit hole to fall down.

[PhantomJaguarr]

28 minutes ago, PrometheanCat2 said:

As I’m reading about the history of nuclear chemistry, the author’s attempting to recreate the problems our forefathers (and foremothers) had to tackle.  Example: slower moving neutrons affect nuclei more than fast moving nuclei. Fun! Good for my brain...

I'm not really a fan of chemistry. My comfort and strength is in applied mathematics. I enjoy reading books like Is God a Mathematician? It tackles the question whether mathematics was discovered or invented.

 

I enjoy learning about atoms, though, when it comes to learning about the origin of the universe and after that moment.

[Godlygamer23]

3 hours ago, PrometheanCat2 said:

2. The moment I start bombarding neutrons at nuclei, the above law fails.  The Law Of Conservation of Energy then takes over. It follows Einstein’s famous equation E = mc2.

I'm 100% all laws that we use confirm each other, but I'm also not an expert, and it would be a good idea to research this using information that already exists - it may have been addressed somewhere. For example, it depends on how we're defining mass and matter.

 

That being said, I did find interesting links that might help you further understand conversation of energy and mass, respectively.

https://en.wikipedia.org/wiki/Mass–energy_equivalence#Conservation_of_mass_and_energy

https://en.wikipedia.org/wiki/Conservation_of_mass#Exceptions_or_caveats_to_mass.2Fmatter_conservation

[captain_to_fire]

1 hour ago, WhiteJaguar77 said:

Is God a Mathematician?

Hmm... probably not. ?

1 hour ago, WhiteJaguar77 said:

enjoy learning about atoms, though, when it comes to learning about the origin of the universe and after that moment.

If we disregard wacky scriptural nonsense at the moment, the most popular is of course the Big Bang and how life started on planet Earth; the most popular is the primordial soup theory. Scientists were able to synthesize organic compounds that are building blocks of living things from inorganic elements in a lab using electricity. 

 

But then it begs the question that even scientists have hard time answering, what makes living things alive if both living and non living things are made up of the same stuff: atoms and molecules? A DNA molecule is just a plain double stranded helix of nitrogenous base, phosphate and a sugar and it’s not alive and yet if inside a cell, it makes us who we are. Chlorophyll in plants is just a pigment if it’s outside the plant and yet plants need them to live. So are we actually dead or alive? 

[Guest]

12 minutes ago, hey_yo_ said:

Hmm... probably not. ?

If we disregard wacky scriptural nonsense at the moment... [snip]...So are we actually dead or alive? 

Glib answer: before my Friday beer, I’m dead!

 

When I really want to disturb my students, I ask them to rattle off the current, biological definition of “life”.

 

Thanks again to all the users who took the time (out of watching the Wan Show or watching “art” on the internet) to share their musings with me. @Godlygamer23 , the links are appreciated.

 

Over & out.