Given the heats of reaction below- Mgs - 2HClaq- MgCl2aq - H2g H - -143 kJ MgOs - 2HCIaq - MgCI2aq - H2Og H - -216 kJ H2g - 1-2O2- H2OI H - -285 kJCalculate the heat for the overall reaction from the above data- Mgs - 1-2O2- MgOs

The correct option is A 212 kJ For the net reaction Mg(s) + 1/2 O_2 → MgO(s) Reaction 1 and reaction 3 need to progress in forward direction and rea ...

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Standard XII

Chemistry

Hess' Law

Given the hea...

Question

Given the heats of reaction below:
$M g (s) + 2 H C l (a q) \to M g C l 2 (a q) + H 2 (g)$
$△ H = - 143 k J$
$M g O (s) + 2 H C I (a q) \to M g C I_{2} (a q) + H_{2} O (g)$
$△ H = - 216 k J$
$H_{2} (g) + 1 / 2 O_{2} \to H_{2} O (I)$
$△ H = - 285 k J$
Calculate the heat for the overall reaction from the above data.
$M g (s) + 1 / 2 O_{2} \to M g O (s)$

- 644 k J

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- 212 k J

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+ 644 k J

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- 74 k J

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+ 74 k J

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Solution

The correct option is A $- 212 k J$
For the net reaction
$M g (s) + 1 / 2 O_{2} \to M g O (s)$
Reaction 1 and reaction 3 need to progress in forward direction and reaction 2 need to progress in backward direction.
$M g (s) + 2 H C l (a q) \to M g C l 2 (a q) + H 2 (g)$
$△ H = - 143 k J$ ...... (1)
$M g C I_{2} (a q) + H_{2} O (g) \to M g O (s) + 2 H C I (a q)$
$△ H = + 216 k J$ ...... (2)
$H_{2} (g) + 1 / 2 O_{2} \to H_{2} O (I)$
$△ H = - 285 k J$ ...... (3)
--------------------------------------------
$M g (s) + 2 H C l (a q) + H_{2} (g) + 1 / 2 O_{2} + M g C l_{2} (a q) + H_{2} O (g) \to M g O (s) + 2 H C l (a q) + M g C l_{2} (a q) + H_{2} (g) + H_{2} O (l)$
Hence, the net reaction is
$M g (s) + 1 / 2 O_{2} \to M g O (s)$
The overall heat would be then:
Heat of Reaction 1 - heat of Reaction 2 + heat of Reaction 3
$Δ H = - 143 k J - (- 216 k J) + (- 285 k J) = - 212 k J$

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Given the heats of reaction below:Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)△H=−143 kJMgO(s)+2HCI(aq)→MgCI2(aq)+H2O(g)△H=−216 kJH2(g)+1/2O2→H2O(I)△H=−285 kJCalculate the heat for the overall reaction from the above data.Mg(s)+1/2O2→MgO(s)