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

C(graphite)+O2(g)CO2(g);  ΔH=xkJ

C(diamond)+C2(g)CO2(g);  ΔH=ykJ [Pb. PET 1985]

(1) (x+y)kJmol1

(2) (xy)kJmol1

(3) (yx)kJmol1

(4) None of these

Concept Questions :-

Thermochemistry
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Given that

2C(s)+2O2(g)2CO2(g);  ΔH=787kJ

H2(g)+12O2(g)H2O(l);  ΔH=286kJ

C2H2(g)+212O2(g)2CO2(g)+H2O(l);ΔH=1301kJ

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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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

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The heat change for the reaction H2+12O2H2O 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 (ΔHfo) of methane [IIT JEE (Screening) 1992]

(1) C(diamond)+2H2(g)=CH4(g)

(2) C(graphite)+2H2(g)=CH4(l)

(3) C(graphite)+2H2(g)=CH4(g)

(4) C(graphite)+4H=CH4(g)

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

(1) 2H2(g)+O2(g)2H2O(l);ΔH=116kcal

(2) H2(g)+12O2(g)H2O(l);ΔH=58kcal

(3) H+(aq.)+OH(aq.)2H2O(l);ΔH=13.7kcal

(4) C2H2(g)+212O2(g)2CO2(g)+H2O(l); ΔH=310kcal

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Based on the following thermochemical equations

H2O(g)+C(s)CO(g)+H2(g);ΔH=131kJ

CO(g)+12O2(g)CO2(g);ΔH=282kJ

H2(g)+12O2(g)H2O(g);ΔH=242kJ

C(s)+O2(g)CO2(g);ΔH=XkJ

The value of X is [CBSE PMT 1992]

(1) –393 kJ

(2) –655 kJ

(3) +393 kJ

(4) +655 kJ

Concept Questions :-

Thermochemistry
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