The half life for the radioactive decay of potassium- 40 to argon- 40 is 1.26 x 109 years. suppose nuclear chemical analysis shows that there is 0.771 mmol of argon-40 for every 1.000 mmol of potassium-40 in a certain sample of rock. calculate the age of the rock. round your answer to 2 significant digits.

Given:

Half life t1/2 for K-40 = 1.26*10⁹ years

Initial amount of K-40, A₀ = 1.000 mmol

Amount of Ar-40 formed = 0.771 mmol

To determine:

The age of the rock

Explanation:

The radioactive decay can be expressed mathematically as:

A = A₀exp(-kt)(1)

where A₀ = initial amount

A = amount after time t

k = decay constant = 0.693/t1/2 (2)

Here: k = 0.693/1.26*10⁹ yr = 0.55 *10⁻⁹ yr⁻¹

Now:

A₀ of K-40= 1.000 mmol

A of K-40 = 1.000 - 0.771 = 0.229 mmol

Based on eq(1)

0.229 = 1.000 exp(-0.55*10⁻⁹t)

t = 2.68*10⁹ years

Ans: Age of rock = 2.7*10⁹ yrs

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 !

ill try to . no promises tho.

explanation: