The heat of atomisation of methane and ethane are and respectively. The longest wavelength of light capable of breaking the C-C bond can be expressed in SI unit as: [2026]

Question

The heat of atomisation of methane and ethane are $' x' {kJ mol}^{- 1}$ and $' y' {kJ mol}^{- 1}$ respectively. The longest wavelength $(λ)$ of light capable of breaking the C-C bond can be expressed in SI unit as: [2026]

Smart Achievers · Accepted Answer

(1)

${CH}_{4} (g) \to C (g) + 4 H (g); Δ_{r} H = x kJ/mol$

$C_{2} H_{6} (g) \to 2 C (g) + 6 H (g); Δ_{r} H = y kJ/mol$

$1000 x = 4 \times ε_{C - H}$

$1000 y = 1 \times ε_{C - C} + 6 \times ε_{C - H}$

$ε_{C - C} = (y - \frac{3 x}{2}) \times 1000 = \frac{h c}{λ} \cdot N_{A}$

$(λ') wavelength of photon = \frac{h c N_{A}}{[4 y - 6 x] \times 250}$

Solution

Q.
The heat of atomisation of methane and ethane are $' x' {kJ mol}^{- 1}$ and $' y' {kJ mol}^{- 1}$ respectively. The longest wavelength $(λ)$ of light capable of breaking the C-C bond can be expressed in SI unit as: [2026]

1 $\frac{N_{A} h c}{250 (4 y - 6 x)}$

2 $N_{A} h c {(y - \frac{6 x}{4})}^{- 1}$

3 $\frac{h c}{1000} {(\frac{y - 6 x}{4})}^{- 1}$

4 $\frac{N_{A} h c}{250 (y - 6 x)}$

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Solution

Q. The heat of atomisation of methane and ethane are 'x' kJ mol-1 and 'y' kJ mol-1 respectively. The longest wavelength (λ) of light capable of breaking the C-C bond can be expressed in SI unit as: [2026]

1 NAhc250(4y-6x)

2 NAhc(y-6x4)-1

3 hc1000(y-6x4)-1

4 NAhc250(y-6x)