Tag: chemical thermodynamics

Questions Related to chemical thermodynamics

Ideal fuel should have high calorific value.

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

  1. True

  2. False

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Correct Option: A
Explanation:

Calorific value is defined as heat produced by complete combustion of a specific quantity of a fuel . It is usually expressed in joules per kilogram. An ideal fuel is one which is having high calorific value.

What is used to measure the calorific value of a substance?

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

  1. Barometer

  2. Bomb calorimeter

  3. Spectrometer

  4. Combustion chamber

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Correct Option: B
Explanation:

Barometer: To measure pressure.

Bomb calorimeter: To measure the heat output of combustion.

Spectrometer: To measure the absorption of light.

Combustion chamber: Chamber used for combustion.

What is the unit of calorific value?

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

  1. kJ/kg

  2. kJ/lit

  3. km/hr

  4. kcal

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Correct Option: A
Explanation:

Calorific value is defined as the amount of energy released during combustion per unit mass of the substance.

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

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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

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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

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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 $=$  $0.9kWh/Nm^3$