Question

If the standard heat of formation of
HCl gas at 25 deg.C is -22.66 Kcal
mole-1, calculate the standard heat
of formation at 60 deg.C. ACp For
HCl is -6.82 cal mol-1 deg-1. *​

Answer 1

Answer:

HCL is 7.83 cal mol-5 deg-9

Answer 2

Given: temperature, T₁ = 25 °C, and T₂ = 60 °C

           standard heat of formation, ΔH₁ at  25 °C = -22.66 kcal/mol

           molar heat capacity at constant pressure, ΔCp= -6.82 cal/mol/°C

To Find: standard heat of formation at  60 °C, ΔH₂.

Solution:

To calculate ΔH₂, the formula used:

• change in enthalpy = molar heat capacity x change in temperature
• Δ H   = ΔCp x ΔT

Applying the above formula:

Δ H   = ΔCp x ΔT

ΔH₂ -  ΔH₁  =  ΔCp x ( T₂ - T₁ )

ΔH₂ - (-22.66)  =  -6.82 x (60 - 25)

and, as 1 kcal = 1000 cal

        or, 1000 cal = 1 kcal

        so, 6.82 cal = 6.82 x 10⁻³ kcal

∴ ΔH₂ - (-22.66)  =  (-6.82 x 10⁻³) x 35

   ΔH₂   =  (-6.82 x 10⁻³) x 35 - 22.66

             = (- 238.7 x 10⁻³) - 22.66

             = - 0.2387 - 22.66

             = - 22.89

   ΔH₂   =  - 22.89 kcal

Hence, the standard heat of formation at  60 °C is - 22.89 kcal.