The standard enthalpy of combustion at 25C of hydrogen, cyclohexene (C6H10) and cyclohexane (C6H12) are -241, -3800 and -3920 kJ mol-1, respectively. Calculate the standard enthalpy of hydrogenation of cyclohexene.

1. -131 kJ mol-1

2. -155 kJ mol-1

3. -167 kJ mol-1

4. -121 kJ mol-1

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Thermochemistry
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A gas mixture consisting of 3.67 litres of ethylene and methane on complete combustion at 25C produces 6.11 litres of CO2. Find out the amount of heat evolved on burning one litre of the gas mixture. The heats of combustion of ethylene and methane are -1423 and -891 kJ mol-1, respectively, at 25C.

1. 30.88 kJ

2. 20.28 kJ

3. 50.88 kJ

4. 60.18 kJ

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Iodine molecule dissociates into atoms after absorbing light of 4500 A. If one quantum of radiation is absorbed by each molecule, calculate the kinetic energy of iodine atoms. Bond energy of I2 is 240 kJ mol-1.

1. 2.16×10-20 J

2. 0.16×10-20 J

3. 5.03×10-20 J

4. 8.32×10-20 J

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Thermochemistry
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From the following data, calculate the enthalpy change for the combustion of cyclopropane at 298 K. The enthalpy of formation of CO2(g), H2O(l) and propene (g) are -393.5, -285.8 and 20.42 kJ mol-1 respectively. The enthalpy of isomerisation of cyclopropane to propene is -33.0 kJ mol-1.

1. -1021.32 kJ mol-1

2. -2091.32 kJ mol-1

3. -5021.32 kJ mol-1

4. -3141.32 kJ mol-1

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The bond dissociation enthalpy of gaseous H2, Cl2 and HCl are 435, 243 and 431 kJ mol-1, respectively. Calculate the enthalpy of formation of HCl gas.

1. -92 kJ mol-1

2. -82 kJ mol-1

3. -21 kJ mol-1

4. -55 kJ mol-1

Concept Questions :-

Enthalpy and It's Type
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The enthalpies of the following reactions are shown alongwith.

12H2g+12O2gOHg ; H=42.09 kJ mol-1H2g2Hg;                      H=435.89 kJ mol-1O2g2Og;                      H=495.05 kJ mol-1

Calculate the O-H bond energies for the hydroxyl radical.

1. 223.18 kJ mol-1

2. 423.38 kJ mol-1

3. 513.28 kJ mol-1

4. 113.38 kJ mol-1

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Thermochemistry
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The heat of combustion of ethylene at 17C and at constant volume is -332.19 kcals. What is the value at constant pressure, given that water is in liquid state ?

1. -131.25 k cals

2. -412.23 k cals

3. -534.12 k cals

4. -333.35 k cals

Concept Questions :-

Enthalpy and It's Type
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For a reaction, A+BAB, cP is given by the equation 40+5×10-3 T JK4 in the temperature range 300-600 K. The enthalpy of the reaction at 300 K -s -25.0 KJ. Calculate the enthalpy of the reaction at 450 K.

Also SNO2=57.5 cal/deg, SO2=49.0 cal/deg, SNO=50.3 cal/deg, SO3=56.8 cal/deg.

1. -10.12 kJ

2. -28.32 kJ

3. -18.72 kJ

4. -8.21 kJ

Concept Questions :-

Enthalpy and It's Type
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A certain vessel X has water and nitrogen gas at a total pressure of 2 atm. and 300 K. All the contents of the vessel are transferred to another vessel Y having half the capacity of the vessel X. The pressiure of N2 in this vessel was 3.8 atm. at 300 K. The vessel Y is heated to 320 K and the total pressure observed was 4.32 atm. Calculate the enthalpy of vapourisation of water assuming it to be independent of temperature. Also assume the volume occupied by the gases in a vessel is equal to the volume of the vessel.

1. 39.637 kJ mol-1

2. 19.531 kJ mol-1

3. 396.37 kJ mol-1

4. 3.9127 kJ mol-1

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Enthalpy and It's Type
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The intermediate SiH2 is formed in the thermal decomposition of silicon hydrides. Calculate Hf of SiH2 given the following reactions

Si2H6g+H2g2SiH4g; H=-11.7 kJ/molSiH4gSiH2g+H2g; H=+239.7 kJ/molHf, Si2H6g=+80.3 kJ mol-1

1. 353 kJ/mol

2. 321 kJ/mol

3. 198 kJ/mol

4. 274 kJ/mol

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Thermochemistry
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