THERMOCHEMISTRY CALCULATIONS
Directions: Calculate the heat energy change that takes place. SHOW ALL WORK. Circle your answer & determine
if the reaction is endothermic or exothermic based on ∆H
.
Example: How much heat is released when 90 g of NO decomposes according to the following equation?
2NO
 N 2 + O2
ΔH°= -180 kJ/mol
Is this ENDOTHERMIC or EXOTHERMIC (circle one)
Use these in your conversion!
90g NO
given
1 mol NO
30.01g NO
From Per. Table
-180 kJ
2 mol NO
ANSWER:
= -269.91 kJ
Ratio of coefficient for NO & the ΔH for this reaction (2NO and -180 kj/mol)
1. How much heat will be released when 6.44 g of Sulfur reacts with excess O2 according to the following
equation?
2S + 3O2 → 2SO3 ΔH° = -791.4kJ
Is this ENDOTHERMIC or EXOTHERMIC? (circle one)
2. How much heat will be released when 4.72 g of Carbon reacts with excess O2 according to the
following equation? How many calories is this?
C + O2 → CO2 ΔH°= -393.5kJ
Is this ENDOTHERMIC or EXOTHERMIC?
3. How much heat will be absorbed when 38.2 g of Bromine reacts with excess H 2 according to the
following equation?
H2 + Br2 → 2HBr ΔH°= 72.80kJ
Is this ENDOTHERMIC or EXOTHERMIC?
4. How much heat will be released when 1.48 g of Chlorine reacts with excess phosphorus according to
the following equation?
2P + 5Cl2 → 2PCl5 ΔH°= -886kJ
Is this ENDOTHERMIC or EXOTHERMIC?
5. How much heat will be released when 4.77 g of ethanol (C2H5OH) reacts with excess O2 according to
the following equation? How many calories is this?
C2H5OH + 3O2 → 2CO2 + 3H2O ΔH = -1366.7kJ Is this ENDOTHERMIC or EXOTHERMIC?
6. How much heat will be absorbed when 13.7 g of Nitrogen reacts with excess O 2 according to the
following equation?
N2 + O2 → 2NO ΔH° = -180kJ
Is this ENDOTHERMIC or EXOTHERMIC?
7. How much heat will be released when 11.8 g of Iron reacts with excess O 2 according to the following
equation?
3Fe + 2O2 → Fe3O4 ΔH° = -1120.5kJ
Is this ENDOTHERMIC or EXOTHERMIC?