Calculate the standard enthalpy change, the standard entropy change, and the sta

Question

Calculate the standard enthalpy change, the standard entropy change, and the standard free energy change for the reaction: N2 (g) + 3 F2 (g) ? 2 NF3 (g) How will the sign of ?G change as the temperature increases?

Explanation / Answer

N2 + 3F2 -- > 2NF3 the standard enthalpy change = 2*( enthalpy of formation of NF3) (as the standard enthalpy of formation of nitrogen and fluorine is 0 by definition) so looking up from the web, enthalpy of formation of NF3 = -31.4KJ/mol so enthalpy change for this rxn = 2*(-31.4) = -62.8KJ similarly the standard entropy change = 2*( entropy of formation of NF3) - (entropy of formation of nitrogen) - 3*(entropy of formation of fluorine) taking all values from the web and putting them the standard entropy change = 2*(260.77) - (191.6) - 3*(202.8) = -0.27846 KJ/K delta G = delta H - T*delta S = delta H + 0.27846T so the value of gibbs free energy will become positive as soon as 0.27846T > delta H and at that point, rxn will become non-spontaneous

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