Acetylene, C 2 H 2 , is a gas commonly used inwelding, and is formed from the re

Question

Acetylene, C2H2, is a gas commonly used inwelding, and is formed from the reaction of calcium carbide,CaC2, with water. Given the thermochemicalequations below, determine the value of the standard enthalpy offormation, DHf0, forC2H2 (g) in kJ/mole.

Before you even begin your work here, what is the overall (ornet) thermochemical equation for formation of acetylene from itscomponent elements?

DH0 = H

CaO (s) + H2O (l) à Ca(OH)2(s)              DH0 =   -65.3 kJ

CaO (s) + 3 C (s) à CaC2 (s) + CO(g)      DH0 = +462.3 kJ

CaCO3 (s) à CaO (s) + CO2(g)        DH0 = +178   kJ

CaC2 (s) + 2 H2O (l) àCa(OH)2 (s) + C2H2(g)    DH0 = -126   kJ

2 C (s) + O2 (g) à 2 CO(g)                       DH0 = -220    kJ

2 H2O (l) à 2 H2 (g) +O2(g)           DH0 = +572    kJ

Explanation / Answer

CaO (s) + H2O (l) ------> Ca(OH)2(s)         :DH1  =   -65.3 kJ    ----( 1)

CaO (s) + 3 C (s) --------> CaC2 (s) + CO(g)      : DH 2 = +462.3kJ     ---- ( 2 )

CaCO3 (s) --------> CaO (s) +CO2 (g)        :DH3 = +178    kJ   ---- ( 3 )

CaC2 (s) + 2 H2O (l) ------->Ca(OH)2 (s) + C2H2(g)    : DH4 = -126 kJ  ---------( 4 )

2 C (s) + O2 (g) ------> 2 CO(g)       :   DH5 = -220    kJ    -------- ( 5)

2 H2O (l) --------> 2 H2 (g)+ O2(g)         :  DH6 = +572    kJ --------( 6 )

Formation of C2H2 is given by the Equation 2C +H2 ----->C2H2    : DH7------- ( 7)

Eq ( 7 ) can be obtained by the following sequence

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