The half life of radon-222 is 3.8 days. how much of a 100g sample is left after 15.2 days

6.2 g  

Explanation:  

In a first-order decay, the formula for the amount remaining after n half-lives is  

where  

N₀ and N are the initial and final amounts of the substance  

1. Calculate the number of half-lives.  

If  

2. Calculate the final mass of the substance.  

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol