Question 8.11: PREDICTING THE SIGN OF ΔS FOR A REACTION Predict whether ΔS°...

PREDICTING THE SIGN OF ΔS FOR A REACTION

Predict whether ΔS° is likely to be positive or negative for each of the following reactions:

(a) H_{2}C=CH_{2}(g)  +  Br_{2}(g)  →  BrCH_{2}CH_{2}Br(l)

(b) 2  C_{2}H_{6}(g)  +  7  O_{2}(g)  →  4  CO_{2}(g)  +  6  H_{2}O(g)

STRATEGY
Look at each reaction, and try to decide whether molecular randomness increases or decreases. Reactions that increase the number of gaseous molecules generally have a positive ΔS, while reactions that decrease the number of gaseous molecules have a negative ΔS.