The heat of transition (ΔHt) of graphite into diamond would be, where

$C\left(\text{graphite}\right)+{O}_{2}\left(g\right)\to C{O}_{2}\left(g\right);\text{\hspace{0.17em}\hspace{0.17em}}\Delta H=x\text{\hspace{0.17em}}kJ$

$C\left(\text{diamond}\right)\text{\hspace{0.17em}}+{C}_{2}\left(g\right)\to C{O}_{2}\left(g\right);\text{\hspace{0.17em}\hspace{0.17em}}\Delta H=y\text{\hspace{0.17em}}kJ$ [Pb. PET 1985]

(1) $\left(x+y\right)\text{\hspace{0.17em}}kJ\text{\hspace{0.17em}}mo{l}^{-1}$

(2) $\left(x-y\right)\text{\hspace{0.17em}}kJ\text{\hspace{0.17em}}mo{l}^{-1}$

(3) $\left(y-x\right)\text{\hspace{0.17em}}kJ\text{\hspace{0.17em}}mo{l}^{-1}$

(4) None of these

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Thermochemistry
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Given that

$2C\left(s\right)+2{O}_{2}\left(g\right)\to 2C{O}_{2}\left(g\right);\text{\hspace{0.17em}\hspace{0.17em}}\Delta H=-787\text{\hspace{0.17em}}kJ$

${H}_{2}\left(g\right)+\frac{1}{2}{O}_{2}\left(g\right)\to {H}_{2}O\left(l\right);\text{\hspace{0.17em}\hspace{0.17em}}\Delta H=-286\text{\hspace{0.17em}}kJ$

${C}_{2}{H}_{2}\left(g\right)+2\frac{1}{2}{O}_{2}\left(g\right)\to 2C{O}_{2}\left(g\right)+{H}_{2}O\left(l\right);\text{\hspace{0.17em}}\Delta H=-1301\text{\hspace{0.17em}}kJ$

Heat of formation of acetylene is [KCET 1989; Orissa JEE 2005]

(1) –1802 kJ

(2) +1802 kJ

(3) –800 kJ

(4) +228 kJ

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Hess's Law
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The enthalpy of combustion at 25°C of H2, cyclohexane (C6H12) and cyclohexene (C6H10) are –241, –3920 and –3800 KJ / mole respectively. The heat of hydrogenation of cyclohexene is [BHU 2005]

(1) – 121 KJ / mole

(2) + 121 KJ / mole

(3) – 242 KJ / mole

(4) + 242 KJ / mole

Concept Questions :-

Hess's Law
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The heat change for the reaction ${H}_{2}+\frac{1}{2}{O}_{2}\to {H}_{2}O$ is called

(1) Heat of reaction

(2) Heat of formation

(3) Heat of vaporisation

(4) None of the above

Concept Questions :-

Thermochemistry
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The heat of neutralisation of a strong acid and a strong alkali is 57.0 kJ mol–1. The heat released when 0.5 mole of HNO3 solution is mixed with 0.2 mole of KOH is [KCET 1991; AIIMS 2002;

(1) 57.0 kJ

(2) 11.4 kJ

(3) 28.5 kJ

(4) 34.9 kJ

Concept Questions :-

Thermochemistry
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A solution of 500 ml of 0.2 M KOH and 500 ml of 0.2 M HCl is mixed and stirred; the rise in temperature is T1. The experiment is repeated using 250 ml each of solution, the temperature raised is T2. Which of the following is true [EAMCET 1987; MP PET 1994]

(1) T1 = T2

(2) T1 = 2T2

(3) T1 = 4T2

(4) T2 = 9T1

Concept Questions :-

Enthalpy and It's Type
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In the reaction for the transition of carbon in the diamond form to carbon in the graphite form, ΔH is –453.5 cal. This points out that [BHU 1981; KCET 1986, 89]

(1) Graphite is chemically different from diamond

(2) Graphite is as stable as diamond

(3) Graphite is more stable than diamond

(4) Diamond is more stable than graphite

Concept Questions :-

Thermochemistry
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Which of the following equations correctly represents the standard heat of formation $\left(\Delta {H}_{f}^{o}\right)$ of methane [IIT JEE (Screening) 1992]

(1) $C\left(diamond\right)\text{\hspace{0.17em}}+2{H}_{2}\left(g\right)=C{H}_{4}\left(g\right)$

(2) $C\left(graphite\right)+2{H}_{2}\left(g\right)=C{H}_{4}\left(l\right)$

(3) $C\left(graphite\right)+2{H}_{2}\left(g\right)=C{H}_{4}\left(g\right)$

(4) $C\left(graphite\right)+4H=C{H}_{4}\left(g\right)$

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In which of the following reactions does the heat change represent the heat of formation of water [EAMCET 1991]

(1) $2{H}_{2}\left(g\right)+{O}_{2}\left(g\right)\to 2{H}_{2}O\left(l\right);\text{\hspace{0.17em}}\Delta H=-116\text{\hspace{0.17em}}kcal$

(2) ${H}_{2}\left(g\right)+\frac{1}{2}{O}_{2}\left(g\right)\to {H}_{2}O\left(l\right);\text{\hspace{0.17em}}\Delta H=-58\text{\hspace{0.17em}}kcal$

(3) ${H}^{+}\left(aq.\right)+O{H}^{-}\left(aq.\right)\to 2{H}_{2}O\left(l\right);\text{\hspace{0.17em}}\Delta H=-13.7\text{\hspace{0.17em}}kcal$

(4) ${C}_{2}{H}_{2}\left(g\right)+2\frac{1}{2}{O}_{2}\left(g\right)\to 2C{O}_{2}\left(g\right)+{H}_{2}O\left(l\right)$; $\Delta H=-310\text{\hspace{0.17em}}kcal$

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Based on the following thermochemical equations

${H}_{2}O\left(g\right)+C\left(s\right)\to CO\left(g\right)+{H}_{2}\left(g\right);\text{\hspace{0.17em}}\Delta H=131\text{\hspace{0.17em}}kJ$

$CO\left(g\right)+\frac{1}{2}{O}_{2}\left(g\right)\to C{O}_{2}\left(g\right);\Delta H=-282\text{\hspace{0.17em}}kJ$

${H}_{2}\left(g\right)+\frac{1}{2}{O}_{2}\left(g\right)\to {H}_{2}O\left(g\right);\text{\hspace{0.17em}}\Delta H=-242\text{\hspace{0.17em}}kJ$

$C\left(s\right)+{O}_{2}\left(g\right)\to C{O}_{2}\left(g\right);\text{\hspace{0.17em}}\Delta H=X\text{\hspace{0.17em}}kJ$

The value of X is [CBSE PMT 1992]

(1) –393 kJ

(2) –655 kJ

(3) +393 kJ

(4) +655 kJ

Concept Questions :-

Thermochemistry