Under which circumstances is the enthalpy of a reaction a positive value?
a)the reaction is endothermic and the products are losing energy.
b)the reaction is exothermic and the products are gaining energy.
c)the reaction is exothermic and the products are losing energy.
d)the reaction is endothermic and the products are gaining energy.

so what is the problem with your lab report and whats the subject of the lab report? i will you

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