Question

Without doing a calculation, predict whether the entropy change will be positive or negative when the following reaction occurs in the direction it is written.
a. CO2(g) + 2H2(g) → CH3OH(l)
b. Br2(l) + H2(g) → 2HBr(g)
c. CH3OH(l) + 3/2O2(g) → CO2(g) + 2H2O(g)
d. 2NH3(g) → N2(g) + 3H2(g)

Answer 1

Answer:

CO2(g) + 2H2(g) → CH3OH(l) negative change in entropy

Br2(l) + H2(g) → 2HBr(g) positive change in entropy

CH3OH(l) + 3/2O2(g) → CO2(g) + 2H2O(g) positive change in entropy

2NH3(g) → N2(g) + 3H2(g) positive change in entropy

Explanation:

The change in entropy of a system is said to be positive when there is an increase in the degree of disorderliness of a system. Recall that entropy is defined as the degree of disorderliness in a system.

When gaseous products are formed in a reaction, the more the increase in entropy of the system. Reactions that yield more gaseous products have a very positive increase in entropy.

Hence all reactions in which there was a positive change in entropy yielded gaseous products.