Tag: introduction to thermodynamics

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

Which of the following is not a state function?


a. $U + PV$      b. $q + w$     c. $\cfrac { q _ {rev} }{ T }$       d. $q$

  1. a

  2. b

  3. c

  4. d
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

When you combust $100.0\ g$ of propane at $500.K$ and $1.00\ atm$ in a closed container, you expected to collect $279\ L$ of carbon dioxide. Instead, when you collect the gas, it measures $651\ L$ in total.
Why have you collected more than your predicted, theoretical yield?

  1. The theoretical yield was calculated incorrectly.

  2. The graduated cylinder used to collect the gas was read incorrectly.

  3. You did not account for the surrounding volume of air.

  4. You did not account for the volume of water vapor that was produced.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\text{The theoretical yield was calculaterd incorrectly.}$

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

For a reaction to be spontaneous in neither direction, which of the following is/are correct regarding the closed system?
(1) ${ \left( \Delta { G } \right)  } _{ T,P }=0$
(2)${ \left( \Delta { G } \right)  } _{ T,P }< 0$
(3) ${ \left( \Delta { G } \right)  } _{ U,V }=0$
(4) ${ \left( \Delta { G } \right)  } _{ U,V }>0$
Codes:

  1. 1,2,3 are correct

  2. 1 and 2 are correct

  3. 2 and 4 are correct

  4. 1 and 3 are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\text{For spontaneous in neither direction:}$

(1) ${ \left( \Delta { G } \right)  } _{ T,P }=0$
(3) ${ \left( \Delta { G } \right)  } _{ U,V }=0$
$\text{is correct.}$

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

Select the state functions among the following:

  1. temperature

  2. entropy

  3. work

  4. enthalpy
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

State function is defined as a system that depends upon the initial and final positions,

so temperature , entropy and enthalpy depends upon the initial and final state, so they are state function but work depends upon the area of PV curve.

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

A system where there is exchange of energy but not of mass is called _________ system.

  1. insulated

  2. isolated

  3. open

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

In thermodynamics, a closed system can exchange energy (as heat or work) but not matter, with its surroundings. An isolated system cannot exchange any heat, work, or matter with the surroundings, while an open system can exchange energy and matter.

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

Temperatures of two hot bodies $B _{1}$ and $B _{2}$ are $100^{\circ}C$ and $80^{\circ}C$ respectively. The temperature of surrounding is $40^{\circ}C$. At $t = 0$, the ratio of rates of cooling of the two bodies (liquid) $R _{1} : R _{2}$ will be:

  1. $3 : 2$
  2. $5 : 4$
  3. $2 : 1$
  4. $4 : 5$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rate of cooling=$\cfrac { dQ }{ dt } \propto \quad \Delta T$ 

$\therefore \cfrac { { R } _{ 1 } }{ { R } _{ 2 } } =\cfrac { { \Delta T } _{ 1 } }{ { \Delta T } _{ 2 } } =\cfrac { 100-40 }{ 80-40 } =\cfrac { 60 }{ 40 } =\cfrac { 3 }{ 2 } $

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

In a closed insulator container, a liquid is stirred with a paddle to increase the temperature. Which of the following is true?

  1. $\triangle U=w\neq O,q=O$
  2. $\triangle U=w=q\neq O$
  3. $\triangle U=O,w=q\neq O$
  4. $w=O,\triangle U=q\neq O$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A closed insulated container, a liquid is stirred with a paddle to increase the temperature, therefore it behave as adiabatic system, $q=0$

$\Delta U=q+w$
$\implies \Delta U=w\neq 0$

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

For an isolated system, the entropy:

  1. Either increases or remains constant

  2. Either decreases or remains constant

  3. Can never decrease

  4. Can never increase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy.