Calculate ΔHf for HCN(g) at 25°C, given the following related reaction at 25°C, 2 NH3(g) + 3 O2(g) + 2 CH4(g) ---> 2 HCN(g) + 6 H2O(g); ΔHrxn = -870.8 kJ and the heats of formation of some species are ΔHf = -80.3 kJ/mol for NH3(g), -74.6 kJ/mol for CH4, and -241.8 kJ/mol for H2O(g). Answers are in kJ/mol.

given, 2 NH3(g) + 3 O2(g) + 2 CH4(g) → 2 HCN(g) + 6 H2O(g); ΔHrxn = -870.8 kJ ΔHf = -80.3 kJ/mol for NH3(g), -74.6 kJ/mol for CH4, and -241.8 kJ/mol for H2O(g) ΔHrxn = ∑∆Hproduct- ∑∆Hreactant = 2∆Hf(HCN) + 6∆Hf(H2O)- 2∆Hf(NH3)-2∆Hf(CH4) The standard formation enthalpy of O2 (g) is zero. -870.8 = 2× ∆Hf(HCN) + 6 × -241.8 -2×-80.3-2×-74.6 -870.8 = 2× ∆Hf(HCN) -1450.8 +160.6 + 149.2 -870.8 = 2× ∆Hf(HCN) -1141 -870.8+1141 = 2× ∆Hf(HCN) 270.2 = 2× ∆Hf(HCN)∆Hf(HCN)= 135.1 kJ/mole Answer: 'Formation enthalpy of HCN is 135.1 kJ/mole'

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Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

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Calculate ΔH_f for HCN(g) at 25°C, given the following related reaction at 25°C,

2 NH₃(g) + 3 O₂(g) + 2 CH₄(g) ---> 2 HCN(g) + 6 H₂O(g); ΔH_rxn = -870.8 kJ

and the heats of formation of some species are ΔH_f = -80.3 kJ/mol for NH₃(g), -74.6 kJ/mol for CH₄, and -241.8 kJ/mol for H₂O(g). Answers are in kJ/mol.

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