Use the molar constant volume heat capacities for gases given in Topic 4C (as multiples for R) to estimate the change in reaction enthalpy of N2 (g) + 3 H2 (g) ---> 2 NH3 (g) when the temperture is increased from 300. K to 500. K. Ignore the vibrational contributions to heat capacity. Is the reaction more or less exothermic at the higher temperature?  AtomsLinear MoleculesNonlinear MoleculesCv,m 3/2 R5/2 R3 RCp,m5/2 R7/2 R4 R

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Asked Nov 4, 2019
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Use the molar constant volume heat capacities for gases given in Topic 4C (as multiples for R) to estimate the change in reaction enthalpy of N2 (g) + 3 H2 (g) ---> 2 NH3 (g) when the temperture is increased from 300. K to 500. K. Ignore the vibrational contributions to heat capacity. Is the reaction more or less exothermic at the higher temperature? 

  Atoms Linear Molecules Nonlinear Molecules
Cv,m  3/2 R 5/2 R 3 R
Cp,m 5/2 R 7/2 R 4 R

 

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Expert Answer

Step 1

The change in enthalpy (ΔH) of each reactant and product is calculated using equation (1). The molar constant pressure heat capacity (Cp,m) for NH3 is 4R. The change in enthalpy of NH3 (ΔH1) is calculated as follows:

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ΔΗ-nC,m ΔΤ (1) ΔΗ, -1 mol x 4R (500 K -300 K) -1 molx 4 x8.314 K'mol"' (500 Κ - 300 K) = 6651.2 J

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Step 2

The molar constant pressure heat capacity (Cp,m) for N2 is 7/2R. The change in enthalpy of N2 (ΔH2) is calculated as follows:

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7 AH2 1 molxx8.314 JK mol1 (500 K -300 K) 2 =5819.8 J

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Step 3

The molar constant pressure heat capacity (Cp,m) for H2 is 7/2R. The change in enthalpy...

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7 AH 1 molxx 8.314 JK'mol"1(500 K -300 K) 2 = 5819.8 J

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