CH2=CH2 +H2O <--> CH3-CH2-OH

Delta H = -10.6 kcal/mol
Delta S = -30.3 cal/Kmol

why is delta S a negative value?

Not quite sure I understand the question.

If we go to the Gibb's free energy equation:

delta G = delta H - (T)(delta S)

where T is the temperature in kelvin

Remember that a more negative value of delta g is more spontaneous, and a large positive value of delta g is less spontaneous.

since both H and S are negative:

delta G = (-H) - (T)(-S)
delta G = (-H) + (T)(S)

thus, the larger the value of T, the more positive the delta G... the LESS spontaneous...

Is this what you are after?

Delta S (entropy change) is a measure of the degree of disorder or randomness in a system. In this reaction, the reactant CH2=CH2 (ethylene) and the product CH3-CH2-OH (ethanol) have different molecular structures. Ethylene consists of two carbon atoms double-bonded to each other, while ethanol has an additional hydrogen atom bonded to one of the carbon atoms in ethylene.

When molecules undergo a chemical change, their arrangement and organization often change. In this reaction, the reactant ethylene is becoming more ordered as it transforms into ethanol. The addition of water (H2O) molecule to ethylene results in the formation of a more structured molecule. Therefore, the reaction leads to a decrease in entropy.

Since the reaction is causing the system to become more ordered and less random, delta S is negative (-30.3 cal/Kmol). The negative value indicates that there is a decrease in the number of microstates available to the molecules, resulting in a reduction in the overall randomness or freedom of motion of the particles involved in the reaction.