Radioactive decay can be described by the following equation in a = in ao- kt where ao is the original amount of the substance, a is the amount of the substance remaining after time t, and k is a constant that is characteristic of the substance. minutes for the radioactive isotope chromium-56, k is 1.17 x 10 if the original amount of chromium-56 in a sample is 34.5 mg, how much time is needed for the amount of chromium- 56 that remains to fall to 20.3 mg?

The amount of time needed is 4.53 minutes.

Explanation:

The equation used to calculate time period follows:

where,

= initial mass of Cr-56 isotope = 34.5 mg

A = mass of the Cr-56 isotope left after the time = 20.3 mg

t = time = ? min

k = rate constant =

Putting values in above equation, we get:

Hence, the amount of time needed is 4.53 minutes.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

answer; 4 electrons;