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Enthalpy of Combustion

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Question

Calculate the efficiency of a fuel cell given the heat of combustion of hydrogen is -286.0 kJ Mol^-1 , and the Gibbs free energy change for the fuel cell is -238 kJ mol^-1

A

63.%

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B

41.5%

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C

73%

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D

83%

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Solution

The correct option is D
83%

Efficiency of fuel cell (? ) = {-238/-286 } x 100 = 83.0% (approx)

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Similar questions

Q. In a fuel cell, methanol is used as fuel and oxygen gas is used as an oxidiser. The reaction is:

{C H}_{3} O H (l) + \frac{3}{2} O_{2} (g) ⟶ \frac{1}{2} C O_{2} (g) + 2 H_{2} O (l)

Calculate standard Gibbs free energy change for the reaction that can be converted into electrical work. If the standard enthalpy of combustion for methanol is

- 726 k J {m o l}^{- 1}

, calculate the efficiency of conversion of Gibbs energy into useful work.

Δ G_{f}^{o}

{C O}_{2}, H_{2} O, {C H}_{3} O H, O_{2}

- 394.36; - 237.13; - 166.27

and zero respectively.

Q. In a fuel cell, methanol is used as a fuel and

O_{2}

is used as an oxidizer. The standard enthalpy of combustion of methanol is

- 726 {kJmol}^{- 1}

. The standard free energies of formation of

C H_{3} O H (l)

C O_{2} (g)

H_{2} O (l)

are − 166.3, −394.4 and

- 237.1 {kJmol}^{- 1}

respectively. The efficiency of the fuel cell will be:

Q. The efficiency of a fuel cell is

80 %

and the standard heat of reaction is

- 300 k J

. The reaction involves two electrons in redox change.

E^{⊖}

for the cell is:

Q. In a fuel cell, methanol is used as fuel and oxygen gas is used as an oxidizer.

The reaction is:

C H_{3} O H (l) + \frac{3}{2} O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)

298 K

, standard Gibb's energies of formation for

C H_{3} O H (l), H_{2} O (l)

C O_{2} (g)

- 166.2, - 237.2

- 394.4 k J m o 1^{- 1}

If standard enthalpy of combustion of methanol is

- 726 k J m o 1^{- 1}

, efficiency of the fuel cell will be:

Q. In a fuel cell (the device used for producing electricity directly from a chemical reaction) methanol is used as a fuel and oxygen gas is used as an oxidizer. The standard enthalpy of combustion of methanol is

- 726 k J m o l^{- 1}

. The standard free energies of formation of

C H_{3} O H (l) . C O_{2 (g)}

H_{2} O (l)

- 166.3, - 394.4

- 237.1 k J m o l^{- 1}

respectively.
The standard free energy change of the reaction will be:

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