Question

Which of the following changes has a decrease in entropy?

CO2(s) → CO2(g)
2H2O(l) → 2H2(g) + O2(g)
H2O(l) → H2O(s)
2KClO3(s) → 3O2(g) + 2KCl(s)

Answer 1

In order to solve this problem you need to consider the states of matter and the amount of products.

If there are more products than reactants than there is an increase in entropy.

States of matter: increasing the motion of particles increases entropy.

Molecular movement:

Solid<Liquid<Gas

Changing states of matter from left to right would be an increase in entropy.

Changing states of matter from right to left would be a decrease in entropy

The answer is number 3

Answer 2

Answer: Option (c) is the correct answer.

Step-by-step explanation:

Entropy is the degree of randomness that is, more randomly the atoms of a substance are moving more will be its entropy.

For example, when ice melts then solid state of water is changing into liquid state. This, means degree of randomness is increasing.

Whereas when water is freezing then molecules are coming closer to each other. As a result, there occurs decrease in degree of randomness.

Thus, we can conclude that
`H2O(l) \rightarrow H2O(s)` is the change that has a decrease in entropy.