Which reactions are spontaneous?

i. c2h5oh(l) + 3o2(g) 2co2(g) + 3h2o(l), g = –36.7 kj
ii. 2c6h6(l) + 15o2(g) 12co2(g) + 6h2o(l), g = –6,405 kj
iii. caco3(s) cao(s) + co2(g), g = 13.0 kj
iv. ni(s) + cl2(g) nicl2(s), g = 1,130.28 kj
a.) i and ii
b.) iii and iv
c.) i and iii
d.) ii and iv

The correct answer is option A.

Explanation:

Gibbs's free energy is defined as the energy which is associated to the chemical reaction that can be used to do work. It is represented as "G".

When Gibbs's free energy is negative, the reaction is said to be spontaneous and when Gibbs's free energy is positive, the reaction is said to be non-spontaneous.

From the given options:

Reaction 1 and reaction 2 has negative Gibbs's free energy and hence, is considered as the spontaneous reactions.

Reaction 3 and reaction 4 has positive Gibbs's free energy and hence, is considered as the non-spontaneous reactions.

Therefore, the correct answer is Option A.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%