Question

a)

Use Hess's law to calculate the enthalpy change for the reaction:

3C(s) + 4H₂(g) + ½O₂(g) → C₃H₈O(l)

Given the following thermochemical equations:

2C₃H₈O(l) + 9O₂(g) → 6CO₂(g) + 8H₂O(l)    ΔH = -4042.6 kJ/mol

C(s) + O₂(g) → CO₂(g)    ΔH = -393.51 kJ/mol

H₂(g) + ½O₂(g) → H₂O(l)    ΔH = -285.83 kJ/mol
(in kJ/mol)

A: -267.7

B: -302.6

C: -341.9

D: -386.3

E: -436.5

F: -493.3

G: -557.4

H: -629.9

b)

Define if the following statement is an endothermic process or exothermic process for the system? In each case, the “system” is underlined.

exothermic or endothermic  water freezing into ice cubes in the freezer
exothermic or endothermic  dry ice subliming into carbon dioxide
exothermic or endothermic  a block of cheese being cooled in a refrigerator

Answer 1

3 C(s) + 4H₂ Ly 1 + 1 o, g) → (3780 ** 01 + 3x ® ] +[4 x® ] gives the above reaction An - 1 x (-4042.6) + 3x (-3 9 3.51) + Yx (-285.83) -302.55 KJ - – 3 02.6