The astronaut then measures the abundance of magnesium on the new planet, obtaining the following results:
isotope abundance
(%) mass
(amu)
24mg 78.99 23.99
25mg
10.00 24.99
26mg 11.01 25.98
what is the atomic mass of magnesium for this planet?

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