The heat of formation of methane at 25° C at a constant pressure is -17.890 kcal. Its heat of formation at constant volume is: [R=1.987 kcal degree -1 mol -1 ]

Question

The heat of formation of methane at 25° C at a constant pressure is -17.890 kcal. Its heat of formation at constant volume is: [R=1.987 kcal degree -1 mol -1 ] (A) -17.297 kcal (B) +17.297 kcal (C) -172.97 kcal (D) +172.97 kcal

Tardigrade Admin · Accepted Answer

Write the equation for heat of formation of

C H_{4}

first to calculate

n_{g}

then calculate

Δ E

Cheat of formation of

C H_{4}

at constant volume) by using formula

Δ E = Δ H + Δ n_{g} RT

Δ H = - 17.890

kcal
Given,

R = 1.987 kcal degree^{- 1} m o l^{- 1}

T = 2 5^{\circ} C = 25 + 273 = 298 K

C (s) + 2 H_{2} (g) ⟶ C H_{4} (g)

Δ n_{g} =

number of moles of gaseous products

-

number of moles of gaseous reactants

= 1 - 2 = - 1

Δ E = Δ H - n RT

= - 17.890 + (- 1 \times 1.987 \times 1 0^{3} \times 298)

= - 17.297

kcal

Q. The heat of formation of methane at 25∘C at a constant pressure is −17.890 kcal. Its heat of formation at constant volume is : [R=1.987 kcal degree −1mol−1 ]

-17.297 kcal

+17.297 kcal

-172.97 kcal

+172.97 kcal

Q. The heat of formation of methane at $2 5^{\circ} C$ at a constant pressure is $- 17.890$ kcal. Its heat of formation at constant volume is : $[R = 1.987$ kcal degree $^{- 1} m o l^{- 1}$ ]