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Question:

C+O_2(g)→CO_2 (i); ΔH=-393kJ mol⁻¹
H_2+1/2O_2→H_2O, .(ii); ΔH=-287.3 kJ mole⁻¹
2CO_2+3H_2O→C_2H_5OH+3O_2 .(iii); ΔH=1366.8 kJ mol⁻¹
Find the standard enthalpy of formation of C_2H_5OH(l).

281.1kJmol⁻¹;

−281.1kJmol⁻¹;

−562.2kJmol⁻¹;

562.2kJmol⁻¹;

Solution:

Correct option is B. −281.1kJmol⁻¹
Given:-
C+O2→CO2 ΔH=−393kJ/mol
2C+2O2→2CO2 ΔH=−786kJ/mol
H2+1/2O2→H2O ΔH=−287.3kJ/mol
3H2+3/2O2→3H2O ΔH=−861.9kJ/mol
2CO2+3H2O→C2H5OH+3O2 ΔH=1366.8kJ/mol
Adding equation(1),(2) (3), we get-
2C+3H2+1/2O2→C2H5OH ΔH=−281.1kJ/mol
Hence, the standard enthalpy of formation of C2H5OH is −281.1kJ/mol.