Tag: chemical thermodynamics

Quizzes (7) Questions (120)

Questions Related to chemical thermodynamics

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

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

  1. Barometer

  2. Bomb calorimeter

  3. Spectrometer

  4. Combustion chamber
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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.

  1. $-12.4$
  2. $-52$
  3. $-24.8$
  4. $-104$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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

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

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


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

  1. $-12.4$
  2. $-52$
  3. $-24.8$
  4. $-104$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. $7.8$ kcal
  2. $15.6$ kcal
  3. $47.0$ kcal
  4. $94$ kcal
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. sulphur

  2. oxygen

  3. hydrogen

  4. carbon
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. pulverised coal

  2. gaseous fuels

  3. fuel oil

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. Gober gas

  2. Refinery gas

  3. Converter gas

  4. Blast furnace gas
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $=$  $0.9kWh/Nm^3$