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Standard XII

Chemistry

Gibbs Free Energy & Spontaneity

When lnK is...

Question

When $ln K$ is plotted against $\frac{1}{T}$ using the Van't Hoff equation, a straight line is expected with a slope equal to:

Δ H^{o} / R T

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- Δ H^{o} / R

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Δ H^{o} / R

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R / Δ H^{o}

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Solution

The correct option is B $- Δ H^{o} / R$
integrating Van't Hoff equation ${\frac {d}{dT}}\ln K_{\mathrm {eq} }={\frac {\Delta H^{\ominus }}{RT^{2}}}$
we get, $\ln {\frac {K_{2}}{K_{1}}}={\frac {-\Delta H^{\ominus }}{R}}\left({\frac {1}{T_{2}}}-{\frac {1}{T_{1}}}\right).$
hence the slope is given in option b.

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Similar questions

Q. Variation of equilibrium constant

K

with temperature

T

is given by van't Hoff equation:

log K = log A - \frac{Δ H^{o}}{2.303 R T}

A graph between

log K

and

T^{- 1}

was a straight line as shown in the figure and having

θ = {tan}^{- 1} (- 0.5)

and

O P = 10

. Calculate:
(a)

Δ H^{o}

(Standard heat of reaction) when

T = 298 K

(b)

A

(pre-exponential factor)
(c) Equilibrium constant

K

298 K

(d)

K

798 K

, if

Δ H^{o}

is independent of temperature

Q. For which one of the following equations is

Δ H^{o}

(reaction) equal to

Δ H^{o}

(formation) for the product?

Q. Calculate

Δ H^{o}

for the reaction,

N a_{2} O (s) + S O_{3} (g) \to N a_{2} S O_{4} (g)

using the following :

N a (s) + H_{2} O (l) \to N a O H (s) + \frac{1}{2} H_{2} (g); Δ H^{o} = - 146 k J

N a_{2} S O_{4} (s) + H_{2} O (l) \to 2 N a O H (s) + S O_{3} (g); Δ H^{o} = + 418 k J

2 N a O (s) + 2 H_{2} (g) \to 4 N a (s) + 2 H_{2} O (l); Δ H^{o} = + 259 k J

Q. The variation of equilibrium constant (

K

) of a certain reaction with temperature (

T

) is

ln K = 3.0 + \frac{2.0 \times 10^{4}}{T}

given

R = 8.3 J K^{- 1} m o l^{- 1}

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Δ H^{o}

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Q. Calculate

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of the reaction

2 N a B r + C l_{2} = 2 N a C l + {B r}_{2}

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Δ H^{o} (N a B r) = - 361 K J / m o l

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When lnK is plotted against 1T using the Van't Hoff equation, a straight line is expected with a slope equal to:

The correct option is B −ΔHo/Rintegrating Van't Hoff equation we get,hence the slope is given in option b.

When $ln K$ is plotted against $\frac{1}{T}$ using the Van't Hoff equation, a straight line is expected with a slope equal to: