Please help 15 points Part c Look at the two question marks between zinc (Zn) and arsenic (AS). At
the time, no elements were known with atomic weights between 65.2
and 75. But Mendeleev predicted that two elements must exist with
atomic weights in this range. What led Mendeleev to predict that two
undiscovered elements existed in that range?

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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