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Calorific value of ethane, in kJ/g if for the reaction is: $2C _2H _6+7O _2\rightarrow 4CO _2+6H _2O;\Delta H=-745.6$ kcal.

chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

  1. $-12.4$

  2. $-52$

  3. $-24.8$

  4. $-104$

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Correct Option: B
Explanation:

Heat of combustion of ethane $=-\frac{745.6}{2}=-372.8\;Kcal\;mol^{-1}=-1559.79\;KJ\;mol^{-1}$       ($1\;cal.=4.2\;J$)

$calorific\; value=\dfrac{heat\;of\;combustion }{gram\;molecular\;weight\;of\;fuel}=-\dfrac{1559.79}{30}=-51.98\approx 52\;KJgm^{-1}$

Calorific value of ethane, in kJ/g if for the reaction :


 $2C _2H _6 + 7O _2 \rightarrow 4CO _2 + 6H _2O; \Delta H = -745.6\ kcal$

chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

  1. $-12.4$

  2. $-52$

  3. $-24.8$

  4. $-104$

Show answer
Correct Option: B
Explanation:

$2C _2H _6+7O _2\rightarrow 4CO _2+6H _2O$; $\Delta H=-745.6KCal$


$\therefore$ Heat of combustion of ethane $=\cfrac {-745.6}{2}=-372.8 Kcal$

                                                                              $=-372.8 \times 4.18 kJ$

                                                                              $=-1558.3 kJ$

Calorific value $=\cfrac {\text{Heat of combustion}}{\text{Molecular weight of }C _2H _6}=- \cfrac {1558.3}{30}=-51.9=-52\ kJ/g$ .


Therefore, the correct option is B.

The heat of combustion of carbon is $94$kcal. The calorific value of carbon is about:

chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

  1. $7.8$ kcal

  2. $15.6$ kcal

  3. $47.0$ kcal

  4. $94$ kcal

Show answer
Correct Option: A
Explanation:

The calorific value of a substance is the heat which it releases during combustion of its $1\text{ } gm$ solid.

Therefore, $\text{Calorific value }(C.V)=\cfrac{\text{Heat of combustion}}{\text{Mol. weight}}\ C+O _2\longrightarrow CO _2;\triangle H=-94Kcal\C.V=\cfrac{-94}{12}Kcal\=-7.83Kcal$

Gross and net calorific value of fuel will be the same :

chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

  1. if its ash content is zero

  2. under no circumstances

  3. if its carbon content is very low

  4. if its hydrogen/hydrogen compound content is zero

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Correct Option: D
Explanation:

The gross or high heating value is the amount of heat produced by the complete combustion of a unit quantity of fuel. 


The net, or lower, value is determined by calculation and equals the gross calorific value minus the latent heat of the water vapor formed from the combustion of hydrogen and from any moisture present in the fuel. 

Gross and net calorific value of a fuel will be the same if its hydrogen compound content is zero.

Hence, option $D$ is correct.

Presence of __________ in a dry gaseous fuel does not contribute to its calorific value.

chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

  1. sulphur

  2. oxygen

  3. hydrogen

  4. carbon

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Correct Option: B
Explanation:

The energy contained in a fuel or food, determined by measuring the heat produced by the complete combustion of a specified quantity of it. This is now usually expressed in joules per kilogram. Oxygen present in dry gaseous fuel does not contribute to its calorific value.

Junker's calorimeter is used to determine the calorific value of ___________.

chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

  1. pulverised coal

  2. gaseous fuels

  3. fuel oil

  4. none of these

Show answer
Correct Option: B
Explanation:

Calorimeter is the instrument used to measure calorific value of heat produced by combustible substances. Junker's calorimeter is used to determine the calorific value of gaseous fuels.

Which of the following gaseous fuels has the lowest calorific value?

chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

  1. Gober gas

  2. Refinery gas

  3. Converter gas

  4. Blast furnace gas

Show answer
Correct Option: D
Explanation:

Calorific value of these gases are listed in table
Gober gas $= $  $5kWh/Nm^3$
refinery gas $= $ $1.5kWh/Nm^3$
Converte gas$ = $ $3kWh/Nm^3$
Blast furnace gas $=$  $0.9kWh/Nm^3$

Gross & net calorific value is the same for ___________.

chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

  1. blast furnace gas

  2. coke oven gas

  3. L.D. converter gas

  4. none of these

Show answer
Correct Option: C
Explanation:

Gross & net calorific value is the same for L.D converter gas. Calorific value is the total quantity of heat liberated by the complete combustion of a unit mass of the fuel in air or oxygen. It is expressed in $kcal/m^3$ or British thermal unit (B.T.U) per cubic foot.

Which of the following has the highest calorific value?

chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

  1. Coal gas

  2. Water gas

  3. Producer gas

  4. Carbon dixode gas

Show answer
Correct Option: A
Explanation:

Calorific value: The amount of energy produced by the complete combustion of a material or fuel.
Coal gas $H _2+CO+CH _4$ has the highest calorific value.

Calorific value is expressed in:

chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

  1. calories per gram

  2. kilojoules per gram

  3. kilocalories per gram

  4. calories per kilogram

Show answer
Correct Option: C
Explanation:

The calorific value of a fuel is the quantity of heat produced by its combustion, at constant pressure and under STP conditions. It is mainly expressed in kcal/g.