Which of the following statements is true? A. Cutting paper is an example of a chemical reaction because a new substance is formed and the process cannot be undone.
B. Freezing water is an example of a chemical reaction because a new substance is formed and the process cannot be undone.
C. Burning paper is an example of a chemical reaction because a new substance is formed and the process cannot be undone.
D. Melting ice is an example of a chemical reaction because a new substance is formed and the process cannot be undone.

the answer is 303.15 or 303

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