Question

1) Which of the following reactions is most likely to have a positive ASsys? (System refers to the reaction.)

a. SiC(s) + 2CO(g) → SiO2(s) + 3C(s)
b. 6CO2(g) + 6H2O(g) → C6H12O6(aq) + O2(g)
c. CO(g) + Cl2(g) → COCl2(g)
d. 2HNO3(1) + NO(g) + 3NO2(g) + H2O(1)

Answer 1

D

Step-by-step explanation:

Of the four given equations, we want to determine which will most likely have a positive ΔS.

A positive ΔS indicates an increase in entropy. Recall that entropy can be described as the "randomness" of a substance. Therefore, gases have the highest entropy, followed by liquids and solids.

Examining each answer choice:

• A is unlikely to have a positive ΔS, as gases are being converted into solids. As a result, entropy is lowered.
• B is likewise unlikely to have a positive ΔS. Multiple moles of gases are being converted into solution and another gas, leading to a decrease in "randomness."
• While all species involved in C are gases, we can see that two moles of gases react to form only one. Because the amount of gases decrease as the reaction proceeds, the amount of "randomness" likewise decreases, indicating a decrease in entropy.

• D is the best answer. One mole of gas reacts to form three moles of gas, thereby increasing "randomness" and hence increasea entropy.