What is the balanced form of the chemical equation shown below? Zn(NO3)2(aq) + Na S(aq) → ZnS(s) + NaNO3(aq)
A. Zn(NO3)2(aq) + Na2S(aq) → ZnS(s) + 2NaNO3(aq)
B. Zn(NO3)2(aq) + Na S(aq) → ZnS(s) + NaNO3(aq)
C. ZnNO3(aq) + Nas(aq) → ZnS(s) + NaNO3(aq)
O D. 2Zn(NO3)2(aq) + Na2S(aq)
ZnS(s) + 3NaNO3(aq)

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