If x1, x2 and x3 are enthalpies of H - H, O = O and O - H bonds respectively, and x4 is the enthalpy of vaporisation of water, estimate the standard enthalpy of combustion of hydrogen.

Question

If x1, x2 and x3 are enthalpies of H - H, O = O and O - H bonds respectively, and x4 is the enthalpy of vaporisation of water, estimate the standard enthalpy of combustion of hydrogen. (A) x1+(x2/2)-2x3+x4 (B) x1+(x2/2)-2x3-x4 (C) x1+(x2/2)-x3-x4 (D) 2x3-x1-(x2/2)-x4

Tardigrade Admin · Accepted Answer

H2(g)+(1/2)O2(g)→ H2O(l);Δ H textcomb ,H2 Δ H textcomb=Δ HH-H+(1/2)Δ HO =O-2Δ HO-H-Δ H textvap=x1+(x2/2)-2x3-x4

Q. If $x_{1}, x_{2}$ and $x_{3}$ are enthalpies of $H - H, O = O$ and $O - H$ bonds respectively, and $x_{4}$ is the enthalpy of vaporisation of water, estimate the standard enthalpy of combustion of hydrogen.

$x_{1} + \frac{x _{2}}{2} - 2 x_{3} + x_{4}$

$x_{1} + \frac{x _{2}}{2} - 2 x_{3} - x_{4}$

$x_{1} + \frac{x _{2}}{2} - x_{3} - x_{4}$

$2 x_{3} - x_{1} - \frac{x _{2}}{2} - x_{4}$

$H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ H_{comb}, H_{2}$
$Δ H_{comb} = Δ H_{H - H} + \frac{1}{2} Δ H_{O} < b r / >= O - 2Δ H_{O - H} - Δ H_{vap} = x_{1} + \frac{x _{2}}{2} - 2 x_{3} - x_{4}$

Q. If x1​,x2​ and x3​ are enthalpies of H−H,O=O and O−H bonds respectively, and x4​ is the enthalpy of vaporisation of water, estimate the standard enthalpy of combustion of hydrogen.

x1​+2x2​​−2x3​+x4​

x1​+2x2​​−2x3​−x4​

x1​+2x2​​−x3​−x4​

2x3​−x1​−2x2​​−x4​