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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If enthalpies of formation of C2H4(g), CO2(g) and H2O(l) at 25°C and 1 atm pressure be 52, – 394 and –286 kJ mol–1 respectively, the enthalpy of combustion of C2H4(g) will be [CBSE PMT 1995; AIIMS 1998; Pb. PMT 1999]

(1) +1412 kJ mol–1

(2) –1412 kJ mol–1

(3) +141.2 kJ mol–1

(4) –141.2 kJ mol–1

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Ozone is prepared by passing silent electric discharge through oxygen. In this reaction [AFMC 1998]

(1) Energy is given out

(2) Energy is absorbed

(3) Oxygen is loaded with energy

(4) Oxygen is dissociated into atoms

Concept Questions :-

Thermochemistry
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Combustion of glucose takes place according to the equation, C6H12O6+6O26CO2+6H2O, ΔH=72kcal. How much energy will be required for the production of 1.6 g of glucose (Molecular mass of glucose = 180 g) [AFMC 1999]

(1) 0.064 kcal

(2) 0.64 kcal

(3) 6.4 kcal

(4) 64 kcal

Concept Questions :-

Enthalpy and It's Type
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Which of the following compounds will absorb the maximum quantity of heat when dissolved in the same amount of water ? The heats of solution of these compounds at 25°C in kJ/mole of each solute is given in brackets [AMU (Engg.) 2000]

(1) HNO3(ΔH=33)

(2) KCl(ΔH=+17.64)

(3) NH4NO3(ΔH=+25.5)

(4) HCl(ΔH=74.1)

Concept Questions :-

Thermochemistry
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A system is changed from state A to state B by one path and from B to A another path. If E1 and E2 are the corresponding changes in internal energy, then [Pb. PMT 2001]

(1) E1+E2=ve

(2) E1+E2=+ve

(3) E1+E2=0

(4) None of these

Concept Questions :-

Internal Energy and work done
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If (i) C+O2CO2, (ii) C+1/2O2CO, (iii) CO+1/2O2CO2, the heats of reaction are Q, –12, –10 respectively. Then Q = [Orissa JEE 2004]

(1) – 2

(2) 2

(3) – 22

(4) – 16

Concept Questions :-

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Adsorption of gases on solid surface is generally exothermic because [IIT JEE (Screening) 2004]

(1) Enthalpy is positive

(2) Entropy decreases

(3) Entropy increases

(4) Free energy increase

Concept Questions :-

Spontaneity and Entropy
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