Which of the following is a process with a negative ΔS?
Which of the following is a process with a negative ΔS?
CO2(s) → CO2(g)
H2O(l) → H2(s)
dissolving sugar in water
CaCO3(s) → CaO(s) + CO2(g)
None of the choices are correct because ΔS cannot be negative.
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Answers & Comments
Negative change in entropy.....
The change in entropy is proportional to the change in the number of microstates in which we find a substance. ("Disorder", though still found in many textbooks and many teachers' dusty old notes, is no longer the preferred way of thinking of entropy.)
Phase changes are often used to illustrate changes in entropy. The number of microstates increases as a substance goes from solid to liquid to gas. The number of microstates increases as a solid dissolves in a solution, and sometimes forms ions.
A positive entropy change means that entropy is increases. A negative entropy change means that entropy is decreasing.
CO2(s) --> CO2(g) ............ entropy increases, sublimation to form a gas
H2O(l) --> H2O(s) ............. entropy decreases, freezing ............ H2O(s), not H2(s)
C12H22O11(s) --> C12H22O11(aq) ........... entropy increases, dissolving
CaCO3(s) --> CaO(s) + CO2(g) .......... entropy increases, a gas is formed
Entropy can be EITHER positive or negative.