Tag: introduction to thermodynamics

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

The state of gas can be described by quoting the relationship between_____________.

  1. pressure, volume, temperature

  2. temperature, amount, pressure

  3. amount, volume, temperature

  4. pressure, volume, temperature, amount
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pressure $(P)$, volume $(V)$, temperature $(T)$, amount $(n)$ etc. are the state variables or state functions.

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

Select incorrect statement(s):

  1. A closed system with all adiabatic boundaries must be an isolated system

  2. Total heat exchange in a cyclic process may be zero

  3. Entropy of a closed system is maximum at equilibrium

  4. Molar gibb's Energy is an extensive property
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Since heat is energy, only two systems can stop it from crossing the boundary closed and isolated system. So yes, adiabatic process can happen in an isolated system. But all adiabatic process need not happen in an isolated system, it can happen in a closed system also.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Two closed vessel $A$ and $B$ of equal volume of $8.21L$ are connected by a narrow tube of negligible volume with open valve. The left hand side container id found to contain $3\ mole \, CO _2$ and $2\ mole$ of $He$ at $400K$. What is the partial pressure of $He$ in vessel $B$ at $500K$?

  1. 2.4 atm

  2. 8 atm

  3. 12 atm

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

partial pressure of $He$ in vessel $B$, 

$PV = nRT$
$P _{He} = \dfrac{nRT}{V} = \dfrac{2\times 8.314\times 400}{8.21} =8atm$

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

Ammonium carbamate dissociates as ${ NH } _{ 2 }COON{ H } _{ 4\left( s \right)  }\leftrightharpoons 2N{ H } _{ 3\left( g \right)  }+{ CO } _{ 2\left( g \right)  }$. In a closed vessel containing ammonium carbamate in equilibrium, ammonia is added such that the partial pressure of ${ NH } _{ 3 }$ now equals to the original total pressure. The ratio of total pressure now to the original pressure is :

  1. $\frac { 27 }{ 31 } $
  2. $\frac { 31 }{ 27 } $
  3. $\frac { 4 }{ 9 } $
  4. $\frac { 5 }{ 9 } $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For the reaction NH2COONH4(s) <=> 2NH3(g) + CO2(g), the initial equilibrium partial pressures are P(NH3) = 2p and P(CO2) = p, so total pressure P1 = 3p. After adding NH3, the new P(NH3) = 3p. Using Kp = (2p)^2 * p = 4p^3, the new equilibrium satisfies 4p^3 = (3p)^2 * P(CO2_new), giving P(CO2_new) = 4p/9. The new total pressure P2 = 3p + 4p/9 = 31p/9. The ratio P2/P1 = (31p/9) / 3p = 31/27.

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

If the density of a certain gas at $30^oC$ and $768 \ torr$ is $1.35 \ kg/{m}^{3}$, the density at STP would be:

  1. $1.48 \ kg/{m}^{3}$
  2. $1.58 \ kg/{m}^{3}$
  3. $1.25 \ kg/{m}^{3}$
  4. $1.4 \ kg/{m}^{3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
From Ideal gas law,

$PM = dRT$

$P _1 = 768\ torr$
$T _1 = 30^0\ C = 303\ K$
$d _1 = 1.35 kg/ m^3$

At STP, 
$T _2 = 273\ K$
$P _2 = 760\ torr$

$\dfrac{P _1}{P _2} = \dfrac{d _1T _1}{d _2T _2}$

$\dfrac{768}{760} = \dfrac{1.35\times 303}{d _2\times 273}$

$d _2 = 1.48 kg/m^3$

Hence, option A is correct.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Assertion: Heat is not a state function

Reason: The change of heat depends upon the

path followed

  1. both A and R are true and R is the correct explanation of A.

  2. both A and R are true but R is not the correct explanation of A.

  3. A is true but R is false.

  4. both A and R are false.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat is a path function. The change of heat depends upon the path followed

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

Which of the following statement(s) is/are incorrect?

  1. For a closed system at rest with no fields, the sum of $q+w$ has the same value for every process that goes from a given state 1 to a given state 2
  2. If a closed system at rest in the absence of external field undergoes an adiabatic process that has $w=0$, then the temperature of system must remain constant

  3. A change in state from state 1 to state 2 produces a greater increase in entropy of the sytem when carried out irreversible than when carried out reversibly

  4. The change in entropy of the system for an adiabatic process in a closed system must be zero
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

A container of volume $1{m}^{3}$ is divided into two equal parts by a partition. One part has an ideal diatomic gas at $300K$ and the other part has vacuum. The whole system is isolated from the surrounding. When the partition is removed, the gas expands to occupy the whole volume. Its temperature will be:

  1. $300K$
  2. ${ 227.5 }^{ o }C$
  3. $455K$
  4. ${455}^{o}C$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is a free expansion of an ideal gas into a vacuum. Since the system is isolated (q=0) and expands into a vacuum (w=0), the internal energy remains constant (delta U = 0). For an ideal gas, internal energy depends only on temperature, so the temperature remains 300K.