ENCE 433 Dr. Alba Torrents

ENVIRONMENTAL ENGINEERING ANALYSIS Fall 1998

Homework Set # 2 Out: September 17 Due: September 24

SOLUTION

1. We will calculate the heat of reaction for the daytime (endothermic) reaction and determine the amount of solar energy absorbed.

kcal/mole -1033.5 -330.9 -68.3

Stoich. coeff. x1 x1 x10

kcal/mole -1033.5 -330.9 -683

H₂₉₈^o = products - reactants = [-330.9 - 683] - [1033.5] = +19.6 kcal/mole

This the amount of heat adsorbed by 1 mole of Na₂SO₄.10H₂O(s) .

We have 322x10³ g / 322 (g/mole) = 1x10³ moles

The heat adsorbed and therefore available to release at night is :

19.6 kcal x 10³ = 1.96 x 10⁴ kcal

2.