Question

Given that,

\[\ce{C_{(s)} + O_{2(g)} -> CO_{2(g)}}\]   ΔH° = -X kJ

\[\ce{2CO_{(g)} + O_{2(g)} -> 2CO_{2(g)}}\]   ΔH° = - Y kJ, then standard enthalpy of formation of carbon monoxide is ________.

Options

• Y - 2X kJ

• 2X - Y kJ

• `("Y" - 2"X")/2`kJ

• `("2X" - "Y")/2`kJ

Answer 1

Given that,

\[\ce{C_{(s)} + O_{2(g)} -> CO_{2(g)}}\]   ΔH° = -X kJ

\[\ce{2CO_{(g)} + O_{2(g)} -> 2CO_{2(g)}}\]   ΔH° = - Y kJ, then standard enthalpy of formation of carbon monoxide is `underline(("Y" - 2"X")/2 "kJ")`.

Explanation:

Multiply equation (1) by (2)

\[\ce{2C_{(s)} + 2O_{2(g)} -> 2CO_{2(g)}}\]  ΔH°= - 2X kJ     ...(i)

Reverse equation (2)

\[\ce{2CO_{2(g)} -> 2CO_{(g)} + O_{2(g)}}\]   ΔH° = Y kJ     ...(ii)
___________________________________________________________________

\[\ce{2C_{(s)} + O_{2(g)} -> 2CO_{(g)}}\]    ΔH° = Y - 2X kJ      ....[Add Eq. (i) & (ii)]

∴ For the formation of 1 mole of CO

i.e., standard enthalpy of formation = `("Y" - 2"X")/2`kJ