What are the spectator ions in Na+ + OH + H+ + Cl + H2O + Na+ + Cl? O A. Na+, OH, H+, and ci-
O B. OH, H+, and H20
C. Na+ and cl
D. OH' and H+

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

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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