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Standard XII

Chemistry

Enthalpy

If enthalpy o...

Question

If enthalpy of formation of $C H_{3} - C H_{3} (g), C H_{3} - C H_{2} - C H_{3} (g) a n d C H_{3} - C H_{2} - C H_{2} - C H_{3} (g)$ are $20$ $k c a l$ /mole, $25$ $k c a l$ /mol and $30$ $k c a l / m o l$ respectively, then enthalpy of formation of $C H_{3} - C H_{2} - C H_{2} - C H_{2} - C H_{2} - C H_{3}$ (g) is:

- 50

k c a l

/mol

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- 40

k c a l

/mol

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- 45

k c a l

/mol

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- 35

k c a l

/mol

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- 55

k c a l

/mol

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Solution

The correct option is B $- 40$ $k c a l$ /mol
If enthalpy of formation of $C H_{3} - C H_{3}$ (g),
The enthalpy of formation per $C H_{2}$ group
$= 5 k c a l / m o l .$
Hence enthalpy of formation of $C_{6} H_{14}$
$= - 30 - 5 \times 2$
$= - 40 k c a l / m o l .$

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Similar questions

In the reaction

$C S_{2} (l) + 3 O_{2} (g) \to C O_{2} (g) + 2 S O_{2} (g) Δ H = - 265 k c a l$

The enthalpies of formation of $C O_{2}$ and $S O_{2}$ are both negative and are in the ratio 4 : 3. The enthalpy of formation of $C S_{2}$ is $+ 26 k c a l / m o l$ . Calculate the enthalpy of formation of $S O_{2}$ .

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Q. In the reaction

C S_{2} (l) + 3 O_{2} (g) \to C O_{2} (g) + 2 S O_{2} (g) △ H = - 265 k c a l

The enthalpies of formation of

C O_{2}

and

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and heat of formation of

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The heat of formation of methyl radical is ?

Q. Estimate the heat of formation of gaseous isoprene

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from the following data;

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If enthalpy of formation of CH3−CH3(g),CH3−CH2−CH3(g)andCH3−CH2−CH2−CH3(g) are 20 kcal /mole,25 kcal /mol and 30 kcal/mol respectively, then enthalpy of formation of CH3−CH2−CH2−CH2−CH2−CH3 (g) is:

The correct option is B −40 kcal/molIf enthalpy of formation of CH3−CH3 (g),The enthalpy of formation per CH2 group =5kcal/mol.Hence enthalpy of formation of C6H14=−30−5×2 =−40kcal/mol.

The correct option is B $- 40$ $k c a l$ /mol
If enthalpy of formation of $C H_{3} - C H_{3}$ (g),
The enthalpy of formation per $C H_{2}$ group
$= 5 k c a l / m o l .$
Hence enthalpy of formation of $C_{6} H_{14}$
$= - 30 - 5 \times 2$
$= - 40 k c a l / m o l .$