CameraIcon

SearchIcon

MyQuestionIcon

1

You visited us 1 times! Enjoying our articles? Unlock Full Access!

Hess' Law

The standard ...

Question

The standard heats of formation of ${C H}_{4} (g), {C O}_{2} (g)$ and $H_{2} O (l)$ are $- 76.2, - 398.8, - 241.6 k J {m o l}^{- 1}$ . Calculate amount of heat evolved by burning $1 m^{3}$ of methane measured under normal (STP) conditions (nearest number in MJ).

Open in App

Solution

$R_{1} : C (s) + 2 H_{2} (l) \to C H_{4} (g)$ ; $Δ H_{1} = - 76.2 k J m o l^{- 1}$
$R_{2} : C (s) + O_{2} (g) \to C O_{2} (g)$ ; $Δ H_{2} = - 398.8 k J m o l^{- 1}$
$R_{3} : H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l)$ ; $Δ H_{3} = - 241.6 k J m o l^{- 1}$
Now, burning methane
$R_{4} : C H_{4} (g) + 2 O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)$ ; $Δ H_{4}$
And
$R_{4} = - R_{1} + R_{2} + 2 R_{3}$
According to Hess's Law of constant heat summation,
$Δ H_{4} = - Δ H_{1} + Δ H_{2} + 2 Δ H_{3}$
$Δ H_{4} = 76.2 - 398.8 + 2 \times (- 241.6) = - 805.8 k J m o l^{- 1}$
1 mole of methane gas at STP occupies 22.4 $l$ volume (assuming ideal gas behavior)
$22.4 l \to 1 m o l e$
$1000 l (1 m^{3}) \to ? m o l e$
$\Rightarrow 1 m^{3}$ of methane $= \frac{1000}{22.4}$ mole of methane
Therefore, the heat evolved by burning $1 m^{3}$ of methane

$= \frac{1000}{22.4} \times 805.8$

$= 35973 k J = 35.973 M J$
Answer = 36

Suggest Corrections

thumbs-up

0

Similar questions

Q. The standard heats of formation of

{C H}_{4} (g), {C O}_{2} (g)

H_{2} O (g)

- 76.2, - 398.8

- 241.6

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

respectively. Calculate the amount of heat evolved by burning

1 m^{3}

of methane measured under normal conditions.

Q. The standard heat of formation of

C H_{4 (g)}, C O_{2 (g)}

H_{2} O_{(g)}

- 76.2, - 398.8, - 241.6

k J m o l^{- 1}

respectively. the amount of heat evolved

(i n k J)

m^{3}

of methane measured under normal conditions is

Q. The standard heat of formation of

C H_{4} (g), C O_{2} (g) a n d H_{2} O (g)

are -76.2, -398.8 and -241.6

k J m o l^{- 1}

respectively. Calculate the amount of heat evolved by burning

1 m^{3}

of methane measured under normal conditions.

Q. The standard heat of formation of

C H_{4 (g)}, C O_{2 (g)}

H_{2} O_{(g)}

- 76.2, - 398.8, - 241.6

k J m o l^{- 1}

respectively. the amount of heat evolved

(i n k J)

m^{3}

of methane measured under normal conditions is

Q. What will be the amount of heat evolved by burning 10 L of methane under standard conditions?
(Given heats of formation of

C H_{4}, C O_{2}

H_{2} O

are -76.2, -398.8 and -241.6 kJ

m o l^{- 1}

View More

Join BYJU'S Learning Program

similar_icon

Related Videos

lock

Thermochemistry

CHEMISTRY

Watch in App

explore_more_icon

Explore more

Standard XII Chemistry

Join BYJU'S Learning Program

CrossIcon