Tag: introduction to thermodynamics

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

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 ?

  1. $PCI _5$ will increase
  2. $PCI _5$ will decrease
  3. $PCI _5$ will remain unaffected
  4. $CI _2$ will increase
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $PCl _5$ .

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

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) $?

  1. $390.3 kJ mol^{-1}$
  2. $1170.9kJ mol^{-1}$
  3. $590 kJ mol^{-1}$
  4. $720 kJ mol^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Identify the 'State function' among the following

  1. q
  2. q $\times$ W

  3. q/W

  4. q + W
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. heat, mass

  2. heat, temperature

  3. temperature, mass

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Which one of the following systems is an example of a closed system?

  1. Some amount of water in equilibrium with its vapour in a closed and insulated vessel

  2. Some amount of hot water enclosed in a closed container which is not insulated

  3. Hot water contained in an open vessel

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When some amount of water is in equilibrium with its vapour in a closed but non insulated vessel, then it will be an example of closed system.

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

Which of the following is not a state function?

  1. U

  2. P

  3. V

  4. q
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

State variables : To define a thermodynamics states of a system, we have to specify the values of certain mesurable quantities. These are called thermodynamic  variable or state variable. 
A system can be completely defined by four variables namely pressure, temperature, volume and composition. A system is said to be in a certain definite state when all of its properties have definite value. 
Between two fixed state the change in the value of state function is same irrespective of the path connection two states. 
Differential of a state function  integerated over a cyclic path returns zero. 
In other words summation of change in state function in a cyclic process is equal to zero.
Example : T, V, P and U (internal energy), H (enthalpy), S are state variables.

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

Warming ammonium chloride with sodium hydroxide in a test tube is an example of:

  1. closed system

  2. isolated system

  3. open system

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

When we are warming ammonium chloride with sodium hydroxide in a test tube, there is exchange of heat as well as mass between system and surrounding. Mass is transferred from the open end of the test tube due to evaporation. Also heat is being exchanged through the walls of test tube.