# Q&A - Ask Doubts and Get Answers

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In which case change in entropy is negative?

• Option 1)

Evapouration of water

• Option 2)

Expansion of a gas at constant temperature

• Option 3)

Sublimation of solid to gas

• Option 4)

$2H_{(g)} \rightarrow H_2_{(g)}$

Gibb's free energy (? G) -   - wherein Gibb's free energy enthalpy of reaction entropy temperature       degree of randomness decreases  entropy decreases and is negative.Option 1)Evapouration of waterOption 2)Expansion of a gas at constant temperatureOption 3)Sublimation of solid to gasOption 4)

For an ideal solution, the correct option is:

• Option 1)

$\Delta_{mix}S = 0$ at constant T and P

• Option 2)

$\Delta_{mix}V \neq 0$ at constant T and P

• Option 3)

$\Delta_{mix}H = 0$ at constant T and P

• Option 4)

$\Delta_{mix}G = 0$ at constant T and P

For an ideal solution, the Gibbs free energy is always negative, thus their mixing is always spontaneous. The volume change of the mixing of ideal solutions is zero. An ideal solution is one in which the enthalpy of the solution is zero  at constant T and P Option 3 is correct.Option 1) at constant T and POption 2) at constant T and POption 3)  at constant T and POption 4) at constant T and P

Under isothermal condition, a gas at 300K expands from 0.1L to 0.25L against a constant external pressure of 2 bar. The work done by the gas is:

[Given that 1L bar = 100 J]

• Option 1)

-30 J

• Option 2)

5 kJ

• Option 3)

25 J

• Option 4)

30 J

We know that the work done is given as: Now, Option 1 is correct.Option 1)-30 JOption 2)5 kJOption 3)25 JOption 4)30 J
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The correct  thermodynamic conditions for the spontaneous reaction at all temperatures is

• Option 1)

$\Delta H< 0\ and\ \Delta S=0$

• Option 2)

$\Delta H> 0\ and\ \Delta S< 0$

• Option 3)

$\Delta H< 0\ and\ \Delta S> 0$

• Option 4)

$\Delta H< 0\ and\ \Delta S< 0$

Spontanous process -   - wherein For spontanouse process must be negative.     For spontaneous  Or,  If  at all temperature. Hence this also satisfies condition for spontaneous reaction. Option 1) This option is incorrect. Option 2) This option is incorrect. Option 3) This option is correct. Option 4) This option is incorrect.
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