Friday

April 25, 2014

April 25, 2014

Number of results: 23,830

**Calculus**

The half-life of Palladium-100 is 4 days. After 12 days a sample of Palladium-100 has been reduced to a mass of 4 mg. What was the initial mass (in mg) of the sample? What is the mass 5 weeks after the start?
*Thursday, February 18, 2010 at 11:49pm by <3*

**physics**

If the physical half-life of sulfur-35 is 87.1 days, and the biologic half-life in the testicle is 632 days, what is its effective half-life in this organ? I know i have to find the time and then the half-life. But im having trouble finding the time A(t)=Ao x e ^ (-0.693) (t...
*Thursday, October 24, 2013 at 9:58pm by Sarah*

**Chemistry **

The metal palladium crystallizes in a face-centered cubic lattice with an edge length of 388.8 pm. What is the density of the palladium?
*Monday, February 4, 2013 at 6:32pm by Sarah*

**math**

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element? half-life: b)How long will it take for a sample of 100 mg to decay to 51 mg? time needed:
*Saturday, May 18, 2013 at 4:06am by Rachel*

**Chemistry**

Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half life of 2.48 * 10^5 years Thorium-230 has half life of 8.0 * 10^4 years Radium-226 has half life of 1.62 * 10^3 years Lead-210 has half life of 20.4 years. The rate constant for the decay of unstable nuclide X...
*Tuesday, March 20, 2012 at 2:23pm by Harry*

**chem**

Can someone please help me with the following questions? 1:Suppose you were given an ancient wooden box. If you analyze the box for carbon-14 activity and find that it is 50% of that of a new piece of wood of the same size, how old is the wood in the box? 2:How old is an ...
*Tuesday, January 2, 2007 at 8:15pm by Margaret*

**Half-Life**

Uranium-238 decays to Lead-206. The half life of Uranium-238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes?
*Sunday, February 19, 2012 at 5:08pm by Noah*

**Chemistry**

Mefenamic acid (Ponstan Forte) has a half life of 2 hours. Naproxen has a half life of 12 to 17 hours. Both are anti inflammatory drugs of apparently similar nature but could someone please explain the difference in half life? Thank you Mike
*Thursday, August 13, 2009 at 4:31am by Mike*

**Chemistry**

a)Calculate the lattice constant a in palladium (Pd).express your answer in angstroms. b) Calculate the distance (in angstroms) between adjacent (110) planes in palladium (Pd). Hint: use your work from part (a).
*Thursday, November 22, 2012 at 8:32am by selly*

**chemistry**

If there are 80 milligrams of a radioactive element decays to 10 milligrams in 30 minutes then what is the elements half life in minutes? Ok i narrowed it down to either 10 or 30...but im rly confused so if u could help it wuld be grea 80 40 1 min 20 2 min 10 3min looks like ...
*Sunday, March 4, 2007 at 7:19pm by jojo*

**life science**

I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
*Thursday, February 7, 2008 at 11:53pm by claire*

**half-life**

1. The half-life of a first-order reaction is 9.89 minutes. How many minutes will have elapsed after 27 half-lives? My answer is 267.03. 2. The half-life of a second-order reaction is 2.508 days. How many days will have elapsed after 8 half-lives? My answer is 5.330. Is this ...
*Wednesday, February 7, 2007 at 5:43pm by Issac*

**linear/exponential**

This question involves the half-life formula. In this exercise, we are to give a half-life for an exponentially decaying quantity. Need answer to the following: The half-life of a drug in the bloodstream is 4 hours. By what factor does the concentration of the drug decrease in...
*Saturday, November 24, 2007 at 4:08pm by kayse*

**Second order half life**

At 100 degrees C , a certain substance undergoes second-order decomposition with a half-life of 26 minutes. If the initial concentration of the substance is 3.9×10−2M , what is the value of the rate constant at 100degrees C? So I put in (1560seconds) 1/2 = 1/ k (3.9×10&#...
*Tuesday, September 21, 2010 at 6:46pm by Sar*

**Chemistry**

(a) Calculate the lattice constant a in palladium (Pd). Use only the information available in the class Periodic Table, and express your answer in angstroms. (b) Calculate the distance (in angstroms) between adjacent (110) planes in palladium (Pd). Hint: use your work from ...
*Thursday, November 22, 2012 at 4:30am by c*

**algebra 2**

element x has a half life of 90 seconds. How much of a 100 gram sample of element x is left after half an hour
*Tuesday, February 15, 2011 at 1:26am by frances*

**Chemistry**

Hydrogen gas dissolves in palladium with the hydrogen molecules going into the spaces between the metal ions. Determine the molarity, molality, and percent by mass of the H2:Pd solution (d=10.8g/cm)containing 0.94g hydrogen gas dissolved in 215 grams of palladium metal.
*Friday, February 17, 2012 at 8:05pm by James*

**Earth Science**

Why is potassium-argon dating most applicable to dating very old rocks? potassium’s long half-life potassium’s short half-life argon’s long half-life argon’s short half-life
*Thursday, February 21, 2013 at 12:09am by Anonymous*

**Chemistry**

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years? A. 2.0 grams of 198 Au B. 2.0 grams of 42 K C. 4.0 grams of 32 P D. 4.0 grams of 60 Co By the way the numbers next to the elements are their atomic masses. thanks ...
*Saturday, March 3, 2007 at 8:50pm by Sanjay*

**Chemistry**

All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639,000 y, what is its half life
*Tuesday, December 11, 2012 at 11:06pm by Matthew*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*Wednesday, September 18, 2013 at 7:12pm by Nadia*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*Thursday, September 19, 2013 at 4:26pm by Nadia*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*Thursday, September 19, 2013 at 7:54pm by Nadia*

**Physcis 30**

Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)? How many will remain after two half-lives (60 seconds)? Three half-lives? So basically, after 30 seconds it will be 50.After 60 sec. ...
*Thursday, January 6, 2011 at 11:13am by Marium*

**Chemistry**

The half-life of iodine -131 is 16 days. If you start with 100 gram sample, how many half-lives have past when you have less than a gram left?
*Sunday, October 28, 2007 at 8:28pm by Taylor*

**college**

. S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
*Monday, May 3, 2010 at 9:51am by kurt*

**college chem**

S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
*Monday, May 3, 2010 at 2:50pm by Anonymous*

**chemistry**

A given reaction has an activation energy of 24.52 kJ/mol. At 25C the half-life is 4 minutes. At what temperature will the half-life be reduced to 20 seconds?
*Saturday, April 9, 2011 at 4:04pm by Eddy*

**chemistry**

Find the number of disintegrations per minute emitted by 1.1 mol of 232-Th in 1 min. The half-life of 232-Th is 1.4 x 1010 year I was able to do this with the following technique: 1.1 x 6.022 x10^23 =6.62x10^23 1.4x10^10=7.358x10^15 minutes I think then it is 6.62x10^23 x 7....
*Thursday, August 2, 2012 at 1:18pm by Nancy *

**Chemistry**

Palladium-107 undergoes â decay (t1/2 = 6.5 x 105 yr) to form silver-107. How long will it take for 0.150 mol of silver-107 to form from 1.25 mol of palladium-107? help please...thank you :)
*Tuesday, December 7, 2010 at 9:12am by Queen*

**help huge test friday science**

I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
*Friday, February 8, 2008 at 12:38am by claire*

**Math **

Suppose a quantity is halvd every 18 years. use the approximate half-life formula to estimate its decay rate. is the half life equation y= 1/2^t1/2 2^1/2t= 1/y t 1/2= log2 (1/y) Where do I put 18 at?
*Friday, December 4, 2009 at 4:05pm by Randi*

**Math - D.E.Q.**

The half-life of a radioactive isotope is the amount of time it takes for a quantity of radioactive material to decay to one-half of its original amount. i) The half-life of Carbon 14 (C-14) is 5230 years. Determine the decay-rate parameter for C − 14.
*Tuesday, January 18, 2011 at 12:07pm by Justin*

**math**

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physics. You purify a sample of 2 grams. One of your colleagues steals half of it, and eight days later you find that 0.1 gram of the radioactive material is ...
*Sunday, October 21, 2012 at 2:34pm by Roseanne*

**Half-life**

After two hours, 1/16 of the initial amount of a radioactive isotope remains undecayed. What is the half-life of the isotope?
*Monday, November 18, 2013 at 8:45am by Andrea*

**chemistry**

How do you find the half-life of an element? Please explain and show me how to do this. I know the answer is 14.3 days, but I don't know how to work it. thank you! the problem is: After 42 days, a 2.0-g sample of phosphous-32 contains only 0.25g of isotope. What is the half-...
*Thursday, December 13, 2007 at 9:07pm by Ryan*

**Chemistry**

The half-life (t1/2) of a first order reaction is 0.100 s. What is the rate constant? a. 6.93 s-1 b. 0.693 s-1 c. 0.0693 s-1 d. 0.144 s-1 e. 3.01 s-1
*Friday, December 6, 2013 at 1:14am by Shines*

**Stats**

Suppose X & Y are two independent stocks' returns with: E(X) = E(Y) =15% and V(X) = 144, V(Y) = 256 Problem 1. Buy half X and half Y, so w1 = w2 = 0.5 and Z = (X+Y)/2 Note: The answer says that the variance is 100 but I thought it would be 200. Since I would be adding half ...
*Friday, September 14, 2012 at 6:07pm by Matt*

**Gen Chem**

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239-Np to decay to 1.00% of its original quantity? I got: close to 15 days. Is this right? I figured that about 1% of the original quantity would be roughly 6.5 Half lives, and since a half ...
*Friday, March 28, 2008 at 5:34pm by Sarah H*

**Alegbra**

Andrew measures the amount of a very unstable substance to be 100 moles. The half-life of this substance is 3 days (after 3 days, half is gone). Write an exponential function that models this situation where y is the amount of substance and x is time in days. Thank you for ...
*Tuesday, May 1, 2012 at 6:58pm by Jessica*

**Chem Class**

The rate constant of a first-order process that has a half-life of 225 s is ?????? s-1. ok so i divided half life of 1st order= 0.693/K k i put 225 and i got 3.08 x 10^-3 is that right?
*Monday, October 25, 2010 at 12:43pm by Laynie*

**algebra**

Andrew measures they amount of a very unstable substance to be 100 moles. the half life of this substance is 3 days(after 3 days, half is gone). write an exponential function that models this situation where Y is the amount of substance and X is time in days. use your equation...
*Friday, April 26, 2013 at 11:11pm by Anonymous*

**Chemistry**

Half-life N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
*Saturday, December 1, 2012 at 2:26am by Paul*

**Math/Radioactive Dating**

How would I calculate the age of a rock only given the amount of each in grams and half-life? 40K decays to 40Ar. Half life of 40K is 1.25 billion years. 40K = 20 grams 40Ar= 5 grams I think the formula is Final Amount of 40K = Initial Amount of 40K * (1/2)^(time/half-life) If...
*Saturday, February 19, 2011 at 2:12pm by Lena*

**Science Half Lives**

I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7)
*Tuesday, January 25, 2011 at 11:16pm by Krys*

**Chemistry**

K-42 has a half-life of 12.4 hours. If you begin with 250g of K-42, determine how much you will have left after 4 half-lives. How long does 4 half-lives take? please help
*Sunday, May 15, 2011 at 8:29pm by Jazmin *

**Science**

Radioactive substance decays so that after t years, the amount remaining, expressed as a percent of the original amount, is A(t)=100(1.6)^(-t). a) Determine the function A’, which represent the rate of decay of the substance. b) what is the half-life for this substance? c) ...
*Tuesday, March 6, 2012 at 11:03pm by jessica*

**Chemistry**

What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s? Please help me!!
*Tuesday, December 11, 2012 at 10:57pm by Matthew*

**chemistry**

The isotype caesium -137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotype in a sample of caesium to decay to one-sixteenth of its original amount? first half life 1/2 second 1/4 third 1/8 fourth 1/16...
*Tuesday, March 6, 2007 at 7:00am by Charley*

**half life**

If the radiological half life of a material is 31 minutes, and you have 77 grams now, how much did you have 55 minutes ago?
*Thursday, January 13, 2011 at 10:52am by julie*

**half life**

tritium has a half life of 24.3 years .a sample of 0.1 is produced . will tthe mass of tritium change after 24.3 years
*Thursday, April 14, 2011 at 6:40am by Anonymous*

**calculus**

The rate at which an amount of a radioactive substance decays is modeled by the differential equation dA/dt = kA, where A is the mass in grams, t is the time in years, and k is a constant. Answer the following. a) If a 100-gram sample of the radioactive substance decays to 95 ...
*Monday, March 19, 2012 at 12:43pm by ronnieday*

**Chemistry**

In 6.20 h a 100 g sample of ag 112 decays to 25 grams. what is the half life of ag 112. I think the answer is 3.10 but I'm not sure. Thanks in advance =)
*Wednesday, June 15, 2011 at 12:39pm by Jackie*

**Chemistry**

half life of tritium is 12.5 years. how much will remain after 100 years if you started wit 256 grams?
*Thursday, October 14, 2010 at 4:06pm by Anonymous*

**Science**

A certain isotope has a half-life of 12 hrs. How long will it take for 100 ƒÝgr to decay into only 25 ƒÝgr?
*Sunday, July 15, 2012 at 12:37pm by Haley*

**Calculus**

The half-life of Radium-226 is 1590 years. If a sample contains 100 mg, how many mg will remain after 4000 years?
*Friday, November 16, 2012 at 6:43pm by Anonymous *

**science/math**

1) Nobelium has a half-life of 1 hour. If you start with 1 kg, how much will you have by this time tomorrow? 2) You have 90 g of Lawrencium. You step away to watch one episode of "everybody loves raymond." when you return to your scientific studies, you only have 0.088g of ...
*Thursday, November 13, 2008 at 5:52pm by kayla*

**math/science**

1) Nobelium has a half-life of 1 hour. If you start with 1 kg, how much will you have by this time tomorrow? 2) You have 90 g of Lawrencium. You step away to watch one episode of "everybody loves raymond." when you return to your scientific studies, you only have 0.088g of ...
*Thursday, November 13, 2008 at 7:32pm by kayla*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?
*Thursday, February 24, 2011 at 7:53pm by rachel*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?
*Thursday, February 24, 2011 at 7:59pm by rachel*

**UIW**

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239Np to decay to 0.100% of its original quantity
*Thursday, September 19, 2013 at 1:32am by Anonymous*

**chemistry**

a sample of a radioisotope had a mass of 100.0 grams. After exactly 24 days, 6.25 grams remained. The half life of the isotope is _________
*Friday, June 3, 2011 at 7:57am by rick*

**college chem**

a first order reaction has a fifth life of 20 seconds ( the amount of time needed to use up 1/5) a) Prove that the reaction has a constant 1/5 life. b) find the half life.
*Sunday, February 21, 2010 at 10:31pm by hymie*

**CALCULUS PLEASE HELP!!**

suppose m(0) milligrams of a drug are put in the blood of an injection. The amount of drug t hours after the injection is given by m(t)=m(o)e^-kt, for t (=>) 0, where k is the rate constant, which is related to the half life. we also treat oral administration of drugs as an...
*Tuesday, April 17, 2012 at 2:02pm by Jake*

**Advanced Math Help!**

suppose m(0) milligrams of a drug are put in the blood of an injection. The amount of drug t hours after the injection is given by m(t)=m(o)e^-kt, for t (=>) 0, where k is the rate constant, which is related to the half life. we also treat oral administration of drugs as an...
*Tuesday, April 17, 2012 at 2:11pm by Rach*

**CALCULUS PLEASE HELP**

suppose m(0) milligrams of a drug are put in the blood of an injection. The amount of drug t hours after the injection is given by m(t)=m(o)e^-kt, for t (=>) 0, where k is the rate constant, which is related to the half life. we also treat oral administration of drugs as an...
*Tuesday, April 17, 2012 at 7:52pm by Rach*

**Calculus**

A certain radioactive material decays exponetially. The percent, P, of the material left after t years is given by P(t)= 100(1.2)^-t a)Determine the half life of the substance
*Tuesday, April 13, 2010 at 7:43pm by lala*

**Chemistry**

I've figured out most of it. I'm not sure how to find the percentage ofd the isotope. Define the half life. The half-life of a radioisotope is found to be 4.55 minutes. If the decay follows first order kinetics, what percentage of isotope will remain after 2.00 hours if you ...
*Tuesday, March 5, 2013 at 8:57pm by m*

**Chemistry **

If 100.0 g of carbon-14 decays until only 25.0 g of carbon is left after 11,460 y, what is the half-life of carbon-14?
*Tuesday, December 11, 2012 at 11:10pm by Jacob *

**statistics**

A professional basketball player has embarked on a program to study his ability to shoot foul shots. On each day in which a game is not scheduled, he intends to shoot 100 foul shots. He maintains records over a period of 40 days of practice, with the results below. Foul Shots ...
*Saturday, October 3, 2009 at 10:53am by MBAhopeful*

**Physical Science- Help Please!**

Suppose that you are given a 100 gram sample of a radioactive substance with a half-life of 32 days. How many grams will be left after 192 days?
*Wednesday, December 5, 2012 at 4:13pm by Molly*

**Chemistry - Half-life**

Phosphene decomposes to phosphorus and hydrogen in a first order mechanism. 4PH3(g) --> P4(g) + 6H2(g) This reaction's half-life is 35.0 s at 680 degrees C. If you had 520 mmHg of phosphene in an 8.00-L flask, how long does it take for the pressure in the flask to rise to ...
*Wednesday, April 25, 2012 at 5:17pm by Aria*

**chemistry**

A particular reactant decomposes with a half-life of 103 s when its initial concentration is 0.397 M. The same reactant decomposes with a half-life of 213 s when its initial concentration is 0.192 M. what is the reaction order and rate constant
*Saturday, March 24, 2012 at 1:28pm by katie*

**half-life**

ok so i got... the half life of carbon-14 is 5730 years, the relation c+(1/2)^ N/5730 is used to calc. the concentration, c, in parts per trillion remaining n years after death determine the carbon concentration in a 11460 year old bone. please help :)
*Wednesday, June 30, 2010 at 11:10am by bubb*

**half-life**

ok so i got... the half life of carbon-14 is 5730 years, the relation c+(1/2)^ N/5730 is used to calc. the concentration, c, in parts per trillion remaining n years after death determine the carbon concentration in a 11460 year old bone. please help :)
*Wednesday, June 30, 2010 at 11:13am by bubb*

**Chemistry**

The half life of U238 is 4.5 x 10^9 yr. A sample of rock of 1.6 g produces 29 dis/sec. Assuming all radioactivity is due to U238 find percent by mass of U 238. I have tried ln(t)/ln(0)= -kt and still cannot get the answer What I get is A) 4.5x10^9 x365x60x60x24=1.419x10^17 for...
*Sunday, September 22, 2013 at 12:26am by Nancy *

**half-life of radioisotope**

A radioisotope has a half-life of 4 days. How much of a 20-gram sample of this radioisotope remains at the end of each time period? 1) 4 days 2) 8 days
*Friday, October 31, 2008 at 7:23pm by Stephanie*

**chemistry**

the half-life of polonium-218 is 3.0 minutes. what percentage of the original sample remains after 4 half-lives?
*Wednesday, December 10, 2008 at 5:24pm by melissa*

**Science**

Radium has a half-life of 1620 years and decays into radon, which has a half-life of 3.82 days. A 10-gm source of radium is sealed, and the radon produced is pumped off every 24 hours. How many mill curies of radon are pumped off each time?
*Sunday, September 30, 2012 at 3:49am by Nivia*

**science**

If I begin with 100 atoms, how many atoms will be left of carbon 12 in 17,190 yrs if the half life of C12 is 5,730 yrs?
*Wednesday, April 4, 2012 at 4:59pm by betty*

**Science**

43Lb has a half life of 42 minutes. If you start with 100 grams, how many grams will you have after 84 minutes?
*Tuesday, January 28, 2014 at 8:05pm by Sabrina*

**chemistry ugg!**

what is the age of a rock whose Argon 40 / Potassium 40 ratio is 1.55? The half life of Potassium 40 is 1.28 x 10^9 years I am confussed on this question theres no examples in my book but i have to know it can someone explain to me how to get to the answer? You don't say if ...
*Thursday, June 15, 2006 at 6:38pm by Andrew*

**CHEM**

An isotope has a half life of 56 days. It now has 10,000DPM/ml. What will its activity be 100 days from now?
*Wednesday, April 17, 2013 at 5:36pm by Jared*

**Calculas**

suppose m(0) milligrams of a drug are put in the blood of an injection. The amount of drug t hours after the injection is given by m(t)=m(o)e^-kt, for t (=>) 0, where k is the rate constant, which is related to the half life. we also treat oral administration of drugs as an...
*Sunday, April 15, 2012 at 1:26pm by Jake*

**science**

Please help me with this question.... The isotope caesium-137, which has a half-life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotope in a sample of caesium to decay to one-sixteenth of its original amount? k = 0.693/t1/2...
*Monday, February 5, 2007 at 7:15pm by Mary*

**Chemistry **

The half-life of the first order reaction, A to products, is 53.2 s. What was the original concentration, (A)0 in moles per liter, if after 1.8 minutes, the concentration of A is 0.0783 moles per liter? Not sure whether to use integrated rate law or half life law?
*Wednesday, March 23, 2011 at 12:59am by Adrianna*

**CALCULUS PLEASE HELP!!**

suppose m(0) milligrams of a drug are put in the blood of an injection. The amount of drug t hours after the injection is given by m(t)=m(o)e^-kt, for t (=>) 0, where k is the rate constant, which is related to the half life. we also treat oral administration of drugs as an...
*Sunday, April 15, 2012 at 1:53pm by Jake*

**Math**

Bhu had $48, but received $100 as a birthday gift and used the money to pay off her debt. She spent half of the money on a gift for herself. Which expression BEST represents the number of dollars Bhu has left? a.(-48+100)÷2 b.(48+100)÷2 c.-48+100÷2 d.2(48+-100)
*Sunday, February 26, 2012 at 10:43am by Gabriel*

**CHEM**

A particular reactant decomposes with a half-life of 139 seconds when its initial concentration is 0.342 M. The same reactant decomposes with a half-life of 237 seconds when its initial concentration is 0.201. What is the value and unit for this rate constant?
*Saturday, January 25, 2014 at 5:29pm by CHEM *

**chemistry**

The half-life of a reaction was found to be inversely dependent on the concentration of the starting material. Thus, we can say that a. the reaction is zero order b. the reaction is first order c. the reaction is second order d. the reaction starts out first order and changes ...
*Friday, February 17, 2012 at 9:31pm by elvis*

**Chemistry please help!**

A Cesium 137 sample has a measured radioactivity of 50 microcuries.Cesium 137 has a half-life of 30 years. How long will it take this sample to be reduced to a residual radioactivity of 6.25 microcuries? Is there a formula to calculate half life?
*Saturday, February 9, 2008 at 7:49pm by Mary*

**chemistry**

A particular reactant decomposes with a half-life of 103 s when its initial concentration is 0.397 M. The same reactant decomposes with a half-life of 213 s when its initial concentration is 0.192 M. Determine rate order and rate constant.
*Saturday, March 24, 2012 at 10:46am by katie*

**Chem 3A**

please help me with this chemistry problem. Half-Life A radium-226 sample initially contains 0.112 mol. How much radium-226 is left in the sample after 6400 years? The half-life of radium-226 is 1600 years.
*Saturday, July 5, 2008 at 5:28pm by shylo*

**Chemistry(Please check)**

8. The half-life of a reaction was found to be inversely dependent on the concentration of the starting material. Thus, we can say that a. the reaction is zero order b.the reaction is first order c.the reaction is second order d. the reaction starts out first order and changes...
*Monday, February 20, 2012 at 3:07pm by Hannah*

**chemistry**

The half-life of a reaction was found to be inversely dependent on the concentration of the starting material. Thus, we can say that a. the reaction is zero order b. the reaction is first order c. the reaction is second order d. the reaction starts out first order and changes ...
*Saturday, February 18, 2012 at 9:21pm by elvis*

**chemistry**

The half-life of a reaction was found to be inversely dependent on the concentration of the starting material. Thus, we can say that a. the reaction is zero order b. the reaction is first order c. the reaction is second order d. the reaction starts out first order and changes ...
*Saturday, February 18, 2012 at 9:28pm by elvis*

**science**

Carbon-14 has a half-life of approximately 5,730 years. How many half-lives have occurred in a sample that contains 50 percent of the original amount of the parent isotope?
*Monday, July 2, 2012 at 12:11pm by ticie burke*

**chemistry**

A fixed amount of gas initially at 100 K and pressure P1 is expanded from 1 L to 100 L in a piston. The temperature, T2, of the gas at this point is 50 K. The piston is then locked at constant volume V2=100 L and half the gas is pumped out at a constant temperature of T2 . The...
*Monday, December 5, 2011 at 6:51pm by laura *

**economics**

1. DETROIT -- Here's a million-dollar question: How does the global economy connect American car buyers and Russian bureaucrats? One person who can answer is Reg Modlin, an emissions specialist at DaimlerChrysler AG's U.S. unit. Mr. Modlin, like many other auto-industry ...
*Thursday, October 4, 2007 at 11:33am by Chithra*

**Chemistry (Dr.Bob222)**

The half-life of P-32 is 14 days. How long after a sample is delivered can a laboratory wait to use a sample in an experiment if they need at least 10 percent of the original radioactivity? I need help on how to set up this problem. What is the general equation to use for a ...
*Thursday, November 7, 2013 at 5:41pm by K*

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