Combustion, or , is an example of one of the most familiar chemical changes. melting of ice, likewise, is one of the most common examples of physical changes. when a piece of coal burns, combines with the carbon in the coal. the products are carbon dioxide gas, water vapor, and a lot of ash. after careful measurements are taken, the of the reactants (coal and oxygen) is to the mass of the products (carbon dioxide, water vapor, and ash). during the reaction, the quantity of matter is unchanged. similarly, when 10 grams of ice , grams of water is obtained. mass is in this change as well.'

the answer is c i took the test

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

its b it was a compound