Question

I was wondering if someone could check whether is right, and if not why?

The following endothermic reaction was carried out at a constant temperature of 298 K. 2A(1) + B(1) -> 2C(9) What can you determine about AS for this reaction? Select one: O a. AS varies dramatically for each reaction and cannot be predicted based upon simple trends. O b. AS=0 O C. While AS can be predicted for some simple reactions, for this reaction the trends are in opposite directions making it impossible to tell. O d. As>0 e. AS<0

Answer 1

Exothermic reaction at constant T (298 K) :

A(l) + B(l) ------> 2 C (g)

Entropy change ΔS :

Entropy is measurement of randomness in system , more precisely : it is a measure of the energy dispersed in a process.The extent to which energy is dispersed depends on how much energy is transferred as heat. As , heat stimulates random motion in the surroundings.

Phase of system also decides entropy as entropy increases from solid to liquid and liquid to gas.This change in entropy is consistent with localization of matter and energy that accompanies the formation of a solid from a liquid or a liquid from a gas.

There are two factors in this reaction which will determine sign of entropy change :

- 2 moles of liquid reactants converts to 2 moles gas product, thus effect is : ΔS= +ve
- Reaction is exothermic (ΔH< 0 ) so,  the entropy change is negative : ΔS= -ve

'so we have trends in opposite direction , so as per this data it is impossible to tell ΔS'  (C).