Which distinguishes chemical changes from physical changes? A. Physical changes are permanent, while changes are temporary.

B. Chemical changes produce new substances, while physical changes do not.

C. Physical changes alter the substance, while chemical changes maintain the same the same properties.

D. Chemical changes result in a change in mass, while physical changes do not.

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

answer would be option a) they have mobile charged particles.