Question

The H–H bond energy is 430 kJ mol⁻¹ and Cl–Cl bond energy is 240 kJ mol⁻¹. $\Delta H$ for HCl is – 90 kJ/mol. The H–Cl bond energy is about :
(a) 180 kJ mol⁻¹
(b) 360 kJ mol⁻¹
(c) 213 kJ mol⁻¹
(d) 425 kJ mol⁻¹

Answer 1

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H2(g)→2HgΔH(H)=+430KJ/mol

Cl2(g)→2Cl(g)ΔHCl=+240KJ/mol

HCl(g)→H(g)+Cl(g)ΔH(HCl)=?

Bond enthalpy of HCl[ΔHHCl] can be found out as follows .

ΔH=∑ΔH0f(product)−∑ΔH0f(reactantt)

=[ΔH0f(H)+ΔH0f(Cl)]−[ΔH0f(HCl)]

=12×430+12×240−(−90)

=425KJ/mol

Answer 2

H2(g)→2HgΔH(H)=+430KJ/mol

Cl2(g)→2Cl(g)ΔHCl=+240KJ/mol

HCl(g)→H(g)+Cl(g)ΔH(HCl)=?

Bond enthalpy of HCl[ΔHHCl] can be found out as follows .

ΔH=∑ΔH0f(product)−∑ΔH0f(reactantt)

=[ΔH0f(H)+ΔH0f(Cl)]−[ΔH0f(HCl)]

=12×430+12×240−(−90)

=425KJ/mol