Question

Answer the questions on Hess's Law listed below. Please note that you must include units throughout all of your calculations and provide your answer in scientific notation to the correct number of significant digits.

Click on the red flags to the left to review content on scientific notation and significant digits.

Question 1

Iron is made from a reaction of iron oxide with carbon monoxide in the following reaction:

Fe₂O_3(s) + 3 CO_(g) → 2 Fe_(s) + 3 CO_2(g)

Using Hess' Law, calculate the enthalpy of reaction given:

C(s) + O2(g) → CO2(g)		ΔH = -393.5 kJ /mol
2 Fe(s) + 3/2 O2(g) → Fe2O3(s)		ΔH = -824.2 kJ /mol
C(s) + 1/2 O2(g) → CO(g)		ΔH = -110.5 kJ /mol

Question 2

Use Hess' Law to calculate enthalpy of reaction for the following equation:

2 N_2(g) + 5 O_2(g) → 2 N₂O_5(g)

Given:

2 H2(g) + O2(g) → 2 H2O(l)		ΔH = -571.6 kJ /mol
N2O5(g) + H2O(l) → 2 HNO3(l)		ΔH = -76.6 kJ /mol
1/2 N2(g) + 3/2 O2(g) + 1/2 H2(g) → HNO3(l)		ΔH = -174.1 kJ /mol

Question 3

Using standard enthalpies of formation, determine the ΔH_reaction for the following equations:

2 CH₃OH_(l) + 3 O_2(g) → 2 CO_2(g) + 4 H₂O_(g)

Standard Enthalpies of Formation
Compound	ΔHf (kJ/mol)
CO(g)	-110.5
CO2(g)	-393.5
CH3OH(l)	-238.4
H2O(g)	-241.8

Answer 1