Tag: chemical thermodynamics

Questions Related to chemical thermodynamics

Calorific value gives ___________.

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

  1. fuel efficiency

  2. amount of heat

  3. amount of light

  4. none of the above

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Correct Option: A
Explanation:

Calorific value is a measure of heating capacity of fuel. It gives the fuel efficiency.

Which one of the following has the highest calorific value?

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

  1. Kerosene

  2. Biogas

  3. LPG

  4. Petrol

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Correct Option: C
Explanation:

The calorific value of a fuel is the quantity of heat produced by its combustion - at constant pressure and under a conditions known as " normal " of temperature and pressure (i.e. to 0oC and under a pressure of 1,013 mbar). 
The combustion of a fuel product generates water vapor. Certain techniques are used to recover the quantity of heat contained in this water vapor by condensing it. 
The Higher Calorific Value (or Gross Calorific Value - GCV) supposes that the water of combustion is entirely condensed and that the heat contained in the water vapor is recovered. 
The Lower Calorific Value (or Net Calorific Value - NCV) supposes that the products of combustion contains the water vapor. The heat contained in the water vapor is not recovered. 
LPG has a typical specific calorific value of 46.1 MJ/kg.
Calorific value of Bio gas is about 19 to 25 MJ/cubic meter, depending on the methane percentage in the biogas mix.
Heat of combustion of kerosene for lower heating value is 43.1 MJ/kg, and for higher heating value is 46.2 MJ/kg.
Petrol, calorific value of which is 45.8 MJ/kg.
Thus, LPG has highest calorific value among above.

Which of the following compounds has the highest calorific value ?

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

  1. $CH _4$

  2. $C _2H _6$

  3. $H _2$

  4. $C _4H _{10}$

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Correct Option: C
Explanation:

Calorific value is the amount of energy produced by the complete combustion of a molecule. Amongst the given options, $H _{2}$ has the highest calorific value.

In a closed system :

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. energy is not exchanged

  2. matter is exchanged

  3. energy is only exchanged

  4. energy and matter are exchanged

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Correct Option: C
Explanation:

In a closed system Matter is not exchanged but Energy is exchanged.

So option c is correct

Which of the following is a state function ?

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. $q\times w$

  2. $q+w$

  3. $\dfrac{q^2}{w^2}$

  4. $\sqrt{qw}$

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Correct Option: B
Explanation:

Solution:- (B) $q + w$

From first law of thermodynamics,
$\Delta{U} = q + w$
As we know that $\Delta{U}$ is a state function, thus we can say that $q + w$ is a state function.

The following two equilibria exist simultaneously in a closed vessel :
$PCI _5(g) \rightleftharpoons PCI _3(g) + Cl _2(g)$
$COCI _2(g) \rightleftharpoons CO (g) + CI _2 (g)$
If some CO is added into the vessel, then after the equlibrium is attained again, concertration of ?

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. $PCI _5$ will increase

  2. $PCI _5$ will decrease

  3. $PCI _5$ will remain unaffected

  4. $CI _2$ will increase

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Correct Option: C
Explanation:

Given reactions are,

$PCl _5 \rightleftharpoons PCl _3+Cl _2$
$COCl _2\rightleftharpoons CO _{(g)}+Cl _2$
If some $CO$ is added into the vessel, the concentration of $PCl _5$ will remain unaffected, because $CO$ reacts with $Cl _2$ and forms $COCl _2$, not going to effect the concentration of $PCl _5$ .

Bond dissociation enthalphies of ${ H } _{ 2 }\left( g \right) $ and ${ N } _{ 2\left( g \right)  }$ are enthalpy of formation of $N{ H } _{ 3 }\left( g \right) $ is $-46 kJ mol^{-1}$. What is enthalpy of atomization of $N{ H } _{ 3 }\left( g \right) $?

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. $390.3 kJ mol^{-1}$

  2. $1170.9kJ mol^{-1}$

  3. $590 kJ mol^{-1}$

  4. $720 kJ mol^{-1}$

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Correct Option: B

Identify the 'State function' among the following

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. q

  2. q $\times$ W

  3. q/W

  4. q + W

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Correct Option: D
Explanation:

Both work and heat are path functions. Their values depends on the path chosen to reach a particular state.
However, the change in internal energy which is equal to the sum of heat and work, is a state function. Its value is independent of  the path chosen to reach a particular state.

Which is not a state function ?

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. Internal energy

  2. Entropy

  3. Work

  4. Enthalpy

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Correct Option: C
Explanation:

Heat and work are not state functions. Work can't be a state function because it is proportional to the distance an object is moved, which depends on the path used to go from the initial to the final state.

An isolated system is one which neither shows an exchange of _nor _with surroundings.

chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

  1. heat, mass

  2. heat, temperature

  3. temperature, mass

  4. None of these

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Correct Option: A
Explanation:
Heat, mass

In physical science, an isolated system is either 

(1) a thermodynamic system which is completely enclosed by walls through which can pass neither matter nor energy, though they can move around inside it; or 

(2) a physical system so far removed from others that it does not interact with them.

Hence, option A is correct.