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

C(graphite)+O2(g)CO2(g);  ΔH=xkJ

C(diamond)+O2(g)CO2(g);  ΔH=ykJ [Pb. PET 1985]

(1) (x+y)kJmol1

(2) (xy)kJmol1

(3) (yx)kJmol1

(4) None of these

Subtopic:  Thermochemistry |
 76%
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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

(1) –1802 kJ

(2) +1802 kJ

(3) –800 kJ

(4) +228 kJ

Subtopic:  Hess's Law |
 73%
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NEET 2023 - Target Batch - Aryan Raj Singh

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

(1) – 121 KJ / mole

(2) + 121 KJ / mole

(3) – 242 KJ / mole

(4) + 242 KJ / mole

Subtopic:  Hess's Law |
 63%
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The heat change for the reaction H2 (g) +12O2 (g)H2O(l) is called

1. Heat of reaction

2. Heat of formation

3. Heat of vaporization

4. None of the above

Subtopic:  Thermochemistry |
 82%
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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

Subtopic:  Thermochemistry |
 68%
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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

(1) T1 = T2

(2) T1 = 2T2

(3) T1 = 4T2

(4) T2 = 9T1

Subtopic:  Enthalpy & Internal energy |
 54%
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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

(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

Subtopic:  Thermochemistry |
 75%
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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)

Subtopic:  Thermochemistry |
 82%
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In which of the following reactions does the heat change represent the heat of the formation of water

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

Subtopic:  Thermochemistry |
 85%
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Hints

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

Subtopic:  Thermochemistry |
 79%
From NCERT
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