A compound is a pure substance made up of two or more different atoms joined by chemical bonds. Consider the composition of the air in Earth’s atmosphere. Which of the components of air is a compound? (Hint: refer back to your elements notes) How do you know?

Carbon dioxide is a compound

Explanation:

It is formed by chemical combination of carbon and oxygen atoms

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