The half-life of bismuth-210, 210bi, is 5 days. (a) if a sample has a mass of 184 mg, find the amount remaining after 15 days.

- 23.0 mg

Solution:- Radioactive decay obeys first order kinetics and the first order kinetics equation is:

where, is the initial amount of radioactive substance and N is it's amount after time t. k is the decay constant.

From given information, Original amount, of the radioactive substance is 184 mg and we are asked to calculate the amount N after 15 days. It means, t = 15 days

Half life is given as 5 days. From the half life, we could calculate the decay constant k using the equation:

where, is the symbol for half life. let's plug in the value of half like to calculate k:

Let's plug in the values in the first order kinetics equation and solve it for N:

lnN = 3.136

N = 23.0 mg

So, 23.0 mg of Bi-210 would be remaining after 15 days.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !