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Half-life and carbon dating | Nuclear chemistry | Chemistry | Khan Academy

765 ratings | 486801 views
Carbon dating is a real-life example of a first-order reaction. This video explains half-life in the context of radioactive decay. Watch the next lesson: https://www.khanacademy.org/science/chemistry/nuclear-chemistry/radioactive-decay/v/half-life-of-radioactive-isotopes?utm_source=YT&utm_medium=Desc&utm_campaign=chemistry Missed the previous lesson? https://www.khanacademy.org/science/chemistry/nuclear-chemistry/radioactive-decay/v/alpha-beta-and-gamma-decay?utm_source=YT&utm_medium=Desc&utm_campaign=chemistry Chemistry on Khan Academy: Did you know that everything is made out of chemicals? Chemistry is the study of matter: its composition, properties, and reactivity. This material roughly covers a first-year high school or college course, and a good understanding of algebra is helpful. About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content. For free. For everyone. Forever. #YouCanLearnAnything Subscribe to Khan Academy’s Chemistry channel: https://www.youtube.com/channel/UCyEot66LrwWFEMONvrIBh3A?sub_confirmation=1 Subscribe to Khan Academy: https://www.youtube.com/subscription_center?add_user=khanacademy
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Text Comments (112)
Ishita Nager (15 days ago)
Thanks for teaching this in such a chill way, prof!
Bhakti Ghongate (1 month ago)
FYI half life of C- 14 is 5730 yrs
The Cringe World (6 months ago)
Why are you not my teacher ????
Yosef (2 months ago)
He is your teacher. Just over the internet on a website. Doesn't make him any less of a teacher.
Esperanza Ruiz (7 months ago)
thanks for teaching me what my college professor wouldn't
Sid P (9 months ago)
So some of these atoms on a very small level will last many times over it's half-life probability.
RK Education Hub (10 months ago)
https://youtu.be/Z3PNljx0pNE
GHOSTLY pro (11 months ago)
which class
Aryssa Guerrero (1 year ago)
Thank you, this makes so much more sense now.
BENNY BOY (1 year ago)
this guy sucks at explaining. he gives to much info. he needs to be straight to the point
Shanny Park (1 year ago)
Gotta watch this bcoz I forgot how to do this sht and finals is approaching. Pray for my soul
Richard Hambel (1 year ago)
carbon dating is such complete bullcrap it never actually work they dated a seal to be 10000 years old LMAO idiots dont believe this bullcrap there is ZERO evidence of anything being more than 10000 years old this carbon dating bullcrap is just propaganda to push the evolutionist agenda
Will Hester (1 year ago)
hate comment
Will Hester (1 year ago)
hate comment
ARELY FLORES (1 year ago)
why did Carbon-14 go to 2.5g and N-14 to 7.5 shouldn't it been 2.5g of N-14 as well?
Tayyab Hameed (1 year ago)
yep they are inversely proportional(i.e when one quantity increases the other decreases),.........
rimsha jaffri (1 year ago)
No because its only the carbon that is decaying, whilst you're gaining more nitrogen hence why the carbon goes down by 2.5 yet the nitrogen increases by that same amount :)
Vucar (1 year ago)
i've learned so much from this disembodied voice. i wish sal would start a bedtime story series... "its time for a bed time story. a bed...time........ story...... bed time story."
I so read that in his voice lol
Black Knight - GAMING (2 years ago)
Khan! You are a better teacher than my science teacher! I understood everything in 12 minutes while my teacher talks for 50 minutes and no one understands anything.
Noah Marciano (1 year ago)
haha so true!
Omar Abdalla (1 year ago)
Black Knight - GAMING lxk/&/@@psxpls,mkklxplxkkslxllx,mjkjy,. ,Kk
hunter (2 years ago)
if I have a block of a ton C14 lying next to a block of 100g C14, do they also need same time for the half of them to decay? 500 kg vs. 50g lost? THat really makes me confuse
It's Ben Porter (2 years ago)
Yes, because fundamentally the half-life of C-14, defined as 5740 years, is the time at which the probability of any one carbon atom within the sample having decayed is 50%. Thus, if you keep adding more an more carbon atoms, each atom after 5740 years will have a 50% chance of decaying, and half the atoms, by probability, will be nitrogen. Of course, this is completely down to probability and so there may be 40% carbon to 60% nitrogen, but on average, 50% will decay regardless of the amount due to the fact that this probability is the probability of an atom having decayed after the half-life has elapsed. It is a bit like if you had a claw machine which randomly gives away prizes, and on average gives away 50% of its prizes after an hour, where there are 1000 prizes initially. You would expect that after an hour, 500 prizes would remain and 500 prizes would have been won by probability. For this example the remaining prizes would represent Carbon, the prizes given away would represent Nitrogen, and the half life would be one hour. If, however, we started with 2000 prizes, we would still expect that, due to the fact that after one hour the chance of a prize being given away is 50%, that 50% of the prizes would be given away, which is equal to 1000 prizes. Applying this back to your question, due to the fact that the decay is a percentage of the initial mass, it does not matter whether you have 1000 or 1000000 carbon atoms, half will still remain and half will decay as the decay is always proportional to the number of atoms present.
리라 (2 years ago)
isnt one mole of any particle equivalent to 6.023x10^-23? at 1:22 its written "23" ! If its a mistake please fix it.
mohit p (1 year ago)
Infinity lol it is +ve 23
M N (2 years ago)
+Infinity It is 23
Devansh Gandhi (2 years ago)
Thank you, Sal. You're the best! Really, really helpful!
Derek Edmunds (3 years ago)
So as the nitrogen is being formed from carbon, does the nitrogen begin decaying as well?
Ellie zaman (2 years ago)
Yess !!
Vishal Singh (3 years ago)
11:53 Half-Life 3 confirmed.
Insanitee Rap-turr (3 years ago)
+Vishal Singh Ah. I'm glad you saw that joke worked out for me. ;)
HowtoGuru100 (3 years ago)
+Vishal Singh hahaha
Pork Chop (3 years ago)
How is 5740 year half life determined??
Christian Holland (4 months ago)
They observe how fast the sample decays, then put numbers into an equation, and then you have the half-life.
M N (2 years ago)
+Pork Chop I hope this helps. We have an equation that tells us how many number of particles are at given time, t: N(t)=n*e^(-rt) n = measured number of a certain type of particle at t=0. r = decay rate t = time half-life literally means the time it takes for 1/2 of the sample to be transmuted to something else. So in 5740 years, 5g of a 10g sample is transmuted. If the sample size is 5,000kg, then 2,500kg is transmuted. Meaning, the bigger the sample size, the higher the probability of seeing the decay. The number of particles(molecules) can be found by knowing its atomic mass and Avogadro's number. Therefore, N(t), n, and t are all measurable!!! r = ln(2)/T; T=half-life so, N(t) = n*e^(-ln(2)t/T) Now, the only unknown variable is T and we can calculate it!
Pork Chop (3 years ago)
404 not fpound
Vishaal Shiva (3 years ago)
+Pork Chop Yeah I had the same question!!! That is really a big number of years and no one has lived up till then to find out the halflife
Alex yeet (4 years ago)
this is science. not gaming --'
TANMAN55555XBOXONE (6 months ago)
—‘This not gaming is science.
zach silva (4 years ago)
It was all a setup, man, a big setup made to for you to learn.
Insanitee Rap-turr (4 years ago)
Half-Life 3 confirmed.
SNOW Martinez (5 months ago)
Insanitee Rap-turr amazing
Citokyne Studios (6 months ago)
I'm trying to find a video about half lives that doesn't have one of these comments. Let me be the one!
Justin G (4 years ago)
anyone watching this has a chem teacher who is awful or confused the hell out of them and the special people are in both situations
Fire Bolt (10 months ago)
we have this in physics. the tutor is shit
fleshcookie (4 years ago)
I could listen to Sal talk all day.
Anurag Harsh (4 years ago)
Alishaaaaaaa...i love you!! :* I love you too Anurag :*
Enny Enny (5 years ago)
youtube is the new school...:D
libertynindependence (5 years ago)
So there isn't a constant rate of decay?
Dslyexiac (5 years ago)
Uhhhm, that wasn't made by valve...
Dslyexiac (5 years ago)
How do you know he did...
Dslyexiac (5 years ago)
You know he doesn't talk :c
RoomWithAView (5 years ago)
or 7
Janstache (5 years ago)
using paint? XD
Angelos (5 years ago)
nice but I understand all of this, what I want to know is how is the half life of any radio metric material determined?
troller123able (5 years ago)
Its funny when he talks about the ultimate atom going against the odds! LOL
Striversurvivor (5 years ago)
We'll probably never see a 3rd episode of this video.
mo. ack (1 year ago)
just like we'll never see half life 3
Striversurvivor (5 years ago)
Rise and shine, Dr. Khan. Wake up and smell the boredom.
gamefreak22333 (5 years ago)
make it 5 now lol
Whit Long (5 years ago)
lol ikr
Christopher Muñoz (5 years ago)
The continuous moving of the pointer, when you're not writing anything on the black screen, really drives me nuts. I had to get it out lol.
Alex Alexx (5 years ago)
10
collin w (5 years ago)
so this guy is my science teacher now...
HarveyMidnight (5 years ago)
Hahaha! That one actually made me laugh! English isn't even the MOST-SPOKEN of all languages! Oh lord... Hahahaha!
Christie Shull (6 years ago)
What is with the language? I hate english
Tristan Lamb (6 years ago)
thank you, my teacher is fucking retarded. I hope she loses half of her life...
BNMC (10 months ago)
I hope mine loses all their life
Foxtrop13 (6 years ago)
so entropy fucks everything?
Obed Raymond Bagona (6 years ago)
Loved the 'Time Machine' part. Thank you once again, Khan Academy! :D
Karthik Ankar (6 years ago)
if 40 g of x in 2 years gets reduced to 20 g . then , in next two years 20 g should become ZERO g ? ! please reply
Light Of Eyes (10 months ago)
Karthik Ankar no it will become 10g
Mazen Youssef (6 years ago)
impossible. they have tenure -_-
Krnz (6 years ago)
I though this wos half life game
Vtron (6 months ago)
It is not, it's an educational video explaining half-lives
matty18972 (6 years ago)
00:39 mmmm grapes
Mercy S (6 years ago)
O.o ummm.... doesn't he mean Beta radiation?
cherrypies3 (6 years ago)
wtf
Uzaair Shah (6 years ago)
WHAT IS THE NEXT VIDEO?1
MsSrivera09 (6 years ago)
I love you. You are the best teacher ever, you saved me. Thank you! and I love your voice.
pharaohgirgzz (6 years ago)
A language for weird hardcore indian men who live in forests naked and jack off there
pharaohgirgzz (6 years ago)
LOLOLOLOLOLOLOLOLOL go watch the punjabi one.
Faria Fairuz (6 years ago)
T(1/2)=ln2/kamda=ln2Tao N=Noe^-lamdaT(1/2)
justin gonzalez (6 years ago)
...you got me laid on the weekend sir, i didnt have to study so i got it on, in return...i thank you :') by -no longer a virgin
Just-Silver (1 year ago)
too late but... !!!CONGRATS
SgtSprinkles (6 years ago)
Now we just need a guide to kill headcrabs.
futurluv13 (6 years ago)
@kieran080188 what's so funny there?
futurluv13 (6 years ago)
@simon1430 well chemistry is math based....
TheSmallBones (6 years ago)
what the fuck i have a science exam in 2 days and i learned more here than i did in a 1 month unit at school
Marie Clarisse (6 years ago)
wow i learned more in 12 minute than i did in an hour of school
s0m0c (6 years ago)
Gracias.
Avocadoe (6 years ago)
Is this math or chemistry.... -.-
6thHorseMan (6 years ago)
@bb33nnii "microsoft paint is amazing" Sal isn't using MS Paint for his videos.
Pricee123 (6 years ago)
@akinrinmade00 and a-level :D
Eilavesch (7 years ago)
Rise and shine, Mr. Khan. Rise and shine...
92soothsayer (7 years ago)
i knew i'd see references to the game, let alone being one of the top comments
Rob Akin (7 years ago)
gcse life saver !
bb33nnii (7 years ago)
microsoft paint is amazing
Elisabeth Meyer (7 years ago)
Wow, my college prof made a total muck of this in her lecture. After seeing this I can almost get through my homework!
ganana0tube (7 years ago)
haha why do i even go to school...
AntharesProcyon (7 years ago)
@ 09:45 with that google subtitle program: 'So after one house wife you'll just looking at one adam after a five thousand seven hundred" Ah, that makes sense! Anyway, must admit that this is pretty awesome, it really saved my ass for this horrible exam I have soon..
cptmacmillan1111 (7 years ago)
gordon freeman can fix this problem by whacking it by a crowbar X
Collin Blank (8 years ago)
Damn I was hoping the next video would teach us how to build a time machine.
tcmzueck (8 years ago)
"Well anywhere mass is invariant this is not a tremendous amount." Classic.
karmacomacure (8 years ago)
yaaay
KarbineKyle (8 years ago)
Awesome Video! They're Great! Why didn't my teachers back in grade school teach this? They just talked about what was in the book, or just said to study out of the book! I wanted teachers who KNEW HOW to teach! You'd have made an AWESOME TEACHER in my middle or high school! It's great to have someone like you educating people who don't know this or didn't learn this, although I know this already, for the most part, I'm just keeping myself "up to date." THUMBS UP!
Afzal Manzoor (8 years ago)
great video
hacksign000 (9 years ago)
aw why didnt I watch this when I was doing half life ? -.-
Fede (9 years ago)
Half-Life?! Copyright?! Debate?! Exclamation mark?! Not a chance.

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