Question

If enthalpy of an overall reaction $$X \to Y$$  along one route is $${\Delta _r}H$$  and $${\Delta _r}{H_1},{\Delta _r}{H_2},{\Delta _r}{H_3}\,...$$     representing enthalpies of reactions leading to same product $$Y$$  then $${\Delta _r}H$$  is

A. $${\Delta _r}H = {\Delta _r}{H_1} + {\Delta _r}{H_2} + {\Delta _r}{H_3}\,...$$  
B. $${\Delta _r}H = {\Delta _r}{H_1} \times {\Delta _r}{H_2} \times {\Delta _r}{H_3}\,...$$
C. $${\Delta _r}H = {\Delta _r}{H_1} + {\Delta _r}{H_2} - {\Delta _r}{H_3}\,...$$
D. $${\Delta _r}H = \frac{{{\Delta _r}{H_1} \times {\Delta _r}{H_2} \times {\Delta _r}{H_3}}}{2}\,\,...$$
Answer :   $${\Delta _r}H = {\Delta _r}{H_1} + {\Delta _r}{H_2} + {\Delta _r}{H_3}\,...$$
Solution :
This is in accordance with Hess's law.

Releted MCQ Question on
Physical Chemistry >> Chemical Thermodynamics

Releted Question 1

The difference between heats of reaction at constant pressure and constant volume for the reaction : $$2{C_6}{H_6}\left( l \right) + 15{O_{2\left( g \right)}} \to $$     $$12C{O_2}\left( g \right) + 6{H_2}O\left( l \right)$$     at $${25^ \circ }C$$  in $$kJ$$ is

A. $$-$$ 7.43
B. $$+$$ 3.72
C. $$-$$ 3.72
D. $$+$$ 7.43
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Releted Question 2

For which change $$\Delta H \ne \Delta E\,:$$

A. $${H_{2\left( g \right)}} + {I_{2\left( g \right)}} \to 2HI\left( g \right)$$
B. $$HC{\text{l}} + NaOH \to NaC{\text{l}}$$
C. $${C_{\left( s \right)}} + {O_{{2_{\left( g \right)}}}} \to C{o_{{2_{\left( g \right)}}}}$$
D. $${N_2}\left( g \right) + 3{H_2}\left( g \right) \to 2N{H_3}\left( g \right)$$
View Answer
Releted Question 3

$${\text{The}}\,\Delta H_f^0\,{\text{for}}\,C{O_2}\left( g \right),\,CO\left( g \right)\,$$     and $${H_2}O\left( g \right)$$   are $$-393.5,$$  $$-110.5$$  and $$ - 241.8\,kJ\,mo{l^{ - 1}}$$    respectively. The standard enthalpy change ( in $$kJ$$ ) for the reaction $$C{O_2}\left( g \right) + {H_2}\left( g \right) \to CO\left( g \right) + {H_2}O\left( g \right)\,{\text{is}}$$

A. 524.1
B. 41.2
C. -262.5
D. -41.2
View Answer
Releted Question 4

In thermodynamics, a process is called reversible when

A. surroundings and system change into each other.
B. there is no boundary between system and surroundings.
C. the surroundings are always in equilibrium with the system.
D. the system changes into the surroundings spontaneously.
View Answer

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Chemical Thermodynamics

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