Given the balanced equation representing a phase change:
c6h4cl2(s) + energy==> c6h4cl2(g)
which statement describes this change?
(1) it is endothermic, and entropy decreases.
(2) it is endothermic, and entropy increases.
(3) it is exothermic, and entropy decreases.
(4) it is exothermic, and entropy increases.

(2) It is endothermic, and entropy increases.

Explanation: Endothermic reactions are those in which heat is absorbed by the system and exothermic reactions are those in which heat is released by the system.

Entropy is the measure of randomness or disorder of a system. If a system moves from  an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

In the given reaction:

The energy is absorbed by the reactants and thus it is endothermic and the solid reactants are converting to gaseous products, thus the entropy increases.

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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