They give us a measure of the tendency for reduction to occur at a particular electrode. They tell us that all half-reactions must be written as reductions. They give us the absolute potential at the electrode in each half-reaction. They tell us in which direction current will flow in a spontaneous redox reaction.

thats how its supposed to be

answer///carbon;

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