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The standard molar heat of formation of ethane ,CO₂ and water (l) are respectively -21.0,-94.1 and -68.3 Kcal mol⁻1. The standard molar heat of combustion of ethane will be
  • a)
    -372 kcal mol⁻1
  • b)
    162 kcal mol⁻1
  • c)
    -340 kcal mol⁻1
  • d)
    183.5 kcal mol⁻1
Correct answer is option 'A'. Can you explain this answer?
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The standard molar heat of formation of ethane ,CO₂ and water (l...
To find the standard molar heat of combustion of ethane, we need to use the heat of formation values for ethane, CO, and water. The standard molar heat of combustion is defined as the energy released when one mole of a substance undergoes complete combustion in excess oxygen.

The balanced equation for the combustion of ethane is:

C2H6 + 7/2 O2 -> 2 CO2 + 3 H2O

To calculate the standard molar heat of combustion, we need to consider the heat of formation of the reactants and products in the equation.

1. Calculate the heat of formation of the reactants:
Ethane (C2H6): -21.0 kcal/mol
Oxygen (O2): 0 kcal/mol (standard state)
CO: -94.1 kcal/mol
Water (H2O): -68.3 kcal/mol

2. Calculate the heat of formation of the products:
CO2: -94.1 kcal/mol (2 CO molecules)
H2O: -68.3 kcal/mol (3 H2O molecules)

3. Calculate the heat of combustion:
ΔH = (2 * ΔHf(CO2)) + (3 * ΔHf(H2O)) - (1 * ΔHf(C2H6)) - (7/2 * ΔHf(O2))

Substituting the values:
ΔH = (2 * -94.1) + (3 * -68.3) - (-21.0) - (7/2 * 0)
= -188.2 - 204.9 + 21.0
= -372.1 kcal/mol

Therefore, the standard molar heat of combustion of ethane is -372 kcal/mol. The correct answer is option A.
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The standard molar heat of formation of ethane ,CO₂ and water (l) are respectively -21.0,-94.1 and -68.3 Kcal mol⁻1. The standard molar heat of combustion of ethane will bea)-372 kcal mol⁻1b)162 kcal mol⁻1c)-340 kcal mol⁻1d)183.5 kcal mol⁻1Correct answer is option 'A'. Can you explain this answer?
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