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Equilibrium Constant from Nernst Equation

Standard free...

Question

Standard free energies of formation (in kJ/mol) at 298 K are -237.2, -394.4 and -8.2 for $H_{2} O (l), C O_{2} (g)$ and pentane (g), respectively. The value of $E_{c e l l}^{0}$ for the pentane-oxygen fuel cell is:

A

1.0968 V

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B

0.0968 V

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C

1.968 V

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D

2.0968 V

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Solution

The correct option is A $1.0968 V$
$C_{5} H_{12} + 8 O_{2} ⟶ 5 C O_{2} + 6 H_{2} O$

$Δ G = G (p r o d u c t s) - G (r e a c t a n t s) = 5 \times (- 394.4) + 6 \times (- 237.2) - (- 8.2) = - 3387 K j m o l^{- 1}$

To get $E_{c e l l}$ use the equation:

$Δ G = - n F E_{c e l l}$

As O is moving from 0 to -2 oxidation state, n = 32 for this reaction

$- 3387 \times 1000$ $= - 32 \times 96500 \times E_{c e l l}$

$E_{c e l l} = 1.0968 V$

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Similar questions

Q. Standard free energies of formation(in

k J / m o l

298

- 237.2

- 394.4

- 8.2

H_{2} O (I), C O_{2} (g)

and pentane(g) respectively. The value of

E_{c e l l}^{o}

for the pentane-oxygen fuel cell is:

Q. The standard free energies of formation of

H_{2} O_{(l)}, {C O}_{2 (g)}

an n-pentane are

- 237.2 k J,

- 394.4 k J,

- 8.2 k J

. Then the value of

E^{0}

for pentane-oxygen fuel cell is:

Q. If 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) \to C O_{2} (g) + 2 H_{2} O (g)

298 K

standard Gibb’s energies of formation for

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

- 166.2, - 237.2

- 394.4 {kJ mol}^{- 1},

respectively. If the standard enthalpy of combustion of methanol is

- 726 {kJ mol}^{- 1}

, the efficiency of the fuel cell will be:

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, 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:

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