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Standard XII

Chemistry

Introduction of VSEPR

If the heats ...

Question

If the heats of formation of ${A l}_{2} O_{3} (s)$ and ${C r}_{2} O_{3} (s)$ are $1596 k J$ and $1134 k J$ (both exothermic) respectively. Calculate $Δ H$ of the thermite reaction.
${C r}_{2} O_{3} (s) + 2 A l (s) ⟶ 2 C r (s) + {A l}_{2} O_{3} (s)$

64 k J

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- 464 k J

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464 k J

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None of these

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Solution

The correct option is D $- 464 k J$
$Δ H = h e a t o f f o r m a t i o n o f$ $A l_{2} O_{3}$ - $h e a t o f f o r m a t i o n o f C r_{2} O_{3}$
$Δ H$ = $- 1596 - (- 1134) = - 464 K J$

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Similar questions

Q. The enthalpy change for two reactions are given by the equations:

2 C r (s) + \frac{3}{2} O_{2} (g) ⟶ {C r}_{2} O_{3} (s); Δ H = - 1130 k J

C (s) + \frac{1}{2} O_{2} (g) ⟶ C O (g); Δ H = - 110 k J

What is the enthalpy change in

k J

for the following reaction?

3 C (s) + {C r}_{2} O_{3} (s) ⟶ 2 C r (s) + 3 C O (g)

List I	List II
A. Calcination	a. $2 {C u}_{2} S + 3 O_{2} \to 2 {C u}_{2} O + 2 S O_{2}$
B. Roasting	b. ${F e}_{2} O_{3} \cdot n H_{2} O \to {F e}_{2} O_{3} + n H_{2} O$
C. Flux	c. ${C r}_{2} O_{3} + 2 A l \to {A l}_{2} O_{3} + 2 C r$
D. Thermite	d. $S i O_{2} + F e O \to F e S i O_{3}$

Match the following.

Q. When compared to

Δ G^{o}

for the formation of

{A l}_{2} O_{3}

, the

Δ G^{o}

for the formation of

{C r}_{2} O_{3}

is:

${F e}_{2} O_{3}$ + $A l$ $\to$ $F e$ + ${A l}_{2} O_{3}$
This is the reaction used in thermite welding process. Calcium can also be used instead of aluminium in this process.

Q. If the masses of

C r

and

O

are in the ratio

13 : 12

C r O_{3}

, then the ratio of

O

that combines with the same mass of Cr in

{C r}_{2} O_{3}

and

{C r}_{2} O_{3}

is:

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If the heats of formation of Al2O3(s) and Cr2O3(s) are 1596kJ and 1134kJ (both exothermic) respectively. Calculate ΔH of the thermite reaction.Cr2O3(s)+2Al(s)⟶2Cr(s)+Al2O3(s)

The correct option is D −464 kJΔH=heatofformationofAl2O3 - heatofformationofCr2O3 ΔH = −1596−(−1134)=−464KJ

If the heats of formation of ${A l}_{2} O_{3} (s)$ and ${C r}_{2} O_{3} (s)$ are $1596 k J$ and $1134 k J$ (both exothermic) respectively. Calculate $Δ H$ of the thermite reaction.
${C r}_{2} O_{3} (s) + 2 A l (s) ⟶ 2 C r (s) + {A l}_{2} O_{3} (s)$

The correct option is D $- 464 k J$
$Δ H = h e a t o f f o r m a t i o n o f$ $A l_{2} O_{3}$ - $h e a t o f f o r m a t i o n o f C r_{2} O_{3}$
$Δ H$ = $- 1596 - (- 1134) = - 464 K J$