Acetylene, C 2 H 2 , is a gas commonly used inwelding, and is formed from the re
ID: 689909 • Letter: A
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