9. Which of these things is true about the Moon? A
The Moon is always moving around Earth in a circle.
B
The Moon is always in the same position in Earth's sky.
С
The Moon is always moving in many changing patterns around Earth.
D
The Moon is always moving back and forth across Earth's sky.

A and B

Explanation:

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