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In which case change in entropy is negat...

In which case change in entropy is negative?

A

`2H(g)toH_(2)(g)`

B

Evaporation of water

C

Expansion of a gas at constant temperature

D

sublimation of solid to gas.

Text Solution

Verified by Experts

The correct Answer is:
A
Entropy=measurement of disorderness if `trianglen_(g)lt0` then `triangleSlt0`
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For a sponaneous reaction, the free energy change must be negative, Delta G=Delta H-T Delta S, Delta H is the enthalpy change during the reaction. T is the absolute temperature, and Delta S is the change in entropy during the reaction. Consider a reaction such as the formation of an oxide M+O_(2) to MO Dioxygen is used up in the course of this reaction. Gases have a more random structure (less ordered) than liquid or solids. Consequently gases have a higher entropy than liquids and solids. In this reaction S (entropy or randomness) decreases, hence Delta S is negative. Thus, if the temperature is raised then T Delta S becomes more negative,Since, TDelta S is substracted in the equation, then Delta G becomes less negative. Thus, the free energy change increases with the increase in temperature. The free energy changes that occur when one mole of common reactant (in this case dioxygen) is used may be plotted graphically aginst temperature for a number of reactions of metals to their oxides. The following plot is called an Ellingham diagram for metal oxide. Understanding of Ellingham diagram is extremely important for the efficient extraction of metals. As per the Ellingham diagram of oxides which of the following conclusion is true ?

The change in entropy, Delta S is positive for an endothermic reaction, if enthalpy change Delta H occurs at the same temperature T, then the reaction is feasible