1. With the aid of a Hess cycle, determine the enthalpy of the decomposition reaction of sodium nitrate, NaNO3 to sodium nitrite, NaNO2 and oxygen, O2. [5] Enthalpy of formation of NaNO3 = -468 kJ/mol
Enthalpy of formation of NaNO2 = -369kJ/mol

Explanation:

2NaNO₃ = 2NaNO₂ + O₂

NaNO₃    =     NaNO₂   +    1/2 O₂

- 468 kJ           -369 kJ           0  kJ

enthalpy of decomposition reaction

= - 369 - ( - 468 ) kJ

= 99 kJ / mol .      

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