Please help me... Refer to the observations of the test tubes from part A. Determine which metal (or hydrogen) in each test tube is more reactive. Remember that the less reactive metal (or hydrogen) will typically end up in pure form as an element, so no reaction will occur if the less reactive metal (or hydrogen) is the one that begins in pure form.

i do not get it   at all

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