Question

Carbon-14 has a half-life of 5720 years and this is a first order reaction. If a piece of wood has converted 25% of the carbon-14, then how old is it?
A) 11440 years
B) 2375 years
C) 4750 years
D) 4290 years
E) 1430 years
Answer: B

) For a particular first-order reaction, it takes 24 minutes for the concentration of the reactant to decrease to 25% of its initial value. What is the value for rate constant (in s-1) for the reaction?
A) 2.0 × 10-4 s-1
B) 9.6 × 10-4 s-1
C) 1.2 × 10-2 s-1
D) 5.8 × 10-2 s-1
Answer: B
Diff: 3 Page Ref: 13.4

Answer 1

ok i know how to solve the problem but i am having problems with knowning when do i subtract from 100

Answer 2

what was the equation again t1/2=log2/k ?

Answer 3

the first one i would do 100-25
the second i would just do ln[25]=-kt+ln[100]

Answer 4

t1/2= .693/k

Answer 5

kk thx let me look at this

Answer 6

first one
ln[75]=-kt+ln[100]

Answer 7

would you divide 25/100 for the 1st one?

Answer 8

the answer wouldnt be correct you have to do 100-25=75
which confuses me, when do you subtract from 100 and when wouldnt you

Answer 9

I believe since they gave you half life you can subtract from 100, and the 2nd question you do not have half life given

Answer 10

I forgot why, but if you have half life given you can subtract 100

Answer 11

ok i have another question

Answer 12

kk

Answer 13

I got it since carbon 12natural is about 99%, and we are using carbon 14, we subtract 100-25

Answer 14

???

Answer 15

oh i remeber when i solved for that in 1045 ok.

Answer 16

kk

Answer 17

so when i have a half life is when i will subtract from 100 basically

Answer 18

yes when its says carbon 14 then subtract 100

Answer 19

ok i have two more questions and i just posted one of them

Answer 20

kk