Which of these is true about the total amount of energy in a closed system? A) Decreases
B) Destroyed
C) Increases
D) Remains the same

D. remains the same

Explanation:

the energy remains the same in a closed system.

it is stable as it is in group 0 which have full outer shells of electrons

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