An engine is running by burning coal. Which statement is correct? A. The engine created energy to perform work. B. The coal created energy to operate the engine. C. The source of energy was created by the sun. D. The energy used to perform work can be traced back to the sun.

the dependant variable is spilled water

the independent is the heat

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