Which of the following is not a point of evidence that a chemical change has taken place 1. The chemical that go into the reaction change color
2. There is a drastic change in the temperature went to chemicals or mixed together no
3. The products from the chemical reaction change in size/ shape
4. A pungent other is produced from the reaction of two chemicals

it would be a gas formation

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