1. This first problem is meant to give you a chance to work through the “per mol” issue in class
in a context with really easy math. Note that many of the answers to the earlier parts will be
given to you in later parts, but the point is for you to walk through the logic, so make sure you
do so. Consider the following reaction:
C(s) + 2F2(g)  CF4(g)
(a) Find ΔH˚ for this reaction. Your units should come out as kJ/mol.
(b) Spoiler alert: Your answer to part (a) should have been -679.9 kJ/mol. Write out the
following sentence, with the blanks filled in as appropriate: 679.9 kJ of enthalpy are
released when ______ moles of C(s) react with ______ moles of F2(g) to produce ______
moles of CF4(g).
(c) What is the ΔH˚ for this reaction per mole of C(s) that reacts? Per mol of F2(g) that reacts?
Per mole of CF4 that is produced? These aren’t necessarily the same numbers.
(d) You should have found that 679.9 kJ of enthalpy is released per mol of C that reacts, but
that only 340.0 kJ of enthalpy is released per mol of F2 that reacts. Why are these numbers
different?
(e) Finally, calculate the ΔH˚ when exactly 0.34 mol of C reacts with exactly 0.68 mol of F 2.
2. The overall reaction that causes heat packs to get warm is given below:
4Fe(s) + 3O2(g)  2Fe2O3(s)
Find ΔH˚ for the reaction where:
(a) 4 moles of Fe reacts with excess O2
(b) 1 mole of Fe reacts with excess O2
(c) 1 gram of Fe reacts with excess O2
3. The enthalpy change for burning ketene (CH2CO)
CH2CO(g) + 2O2(g)  2CO2(g) + H2O(g)
is ΔH˚ = -981.1 kJ/mol at 25˚C. The enthalpy change for the burning of methane
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
is ΔH˚ = -802.3 kJ/mol at 25˚C. Calculate the enthalpy change at 25˚C for the following
reaction:
2CH4(g) + 2O2(g)  CH2CO(g) + 3H2O(g)
4. (a) Mixtures of fertilizer (ammonium nitrate) and fuel oil (a mixture of long-chain
hydrocarbons such as decane, C10H22) are the basis for powerful explosions. Calculate ΔH˚
for the following reaction [ΔH˚f (C10H22) = 249.7 kJ/mol]
3NH4NO3(s) + C10H22(l) + 14O2(g)  3N2(g) + 17 H2O(g) + 10CO2(g)
(b) Trinitrotoluene (TNT or C7H5N3O6) is another powerful explosive. Calculate ΔH˚ for the
following reaction under standard conditions [ΔH˚ f (C7H5N3O6) = -67.1 kJ/mol]
2C7H5N3O6(s)  12CO(g) + 5H2(g) + 2N2(g) + 2C(s)
(c) What mass of TNT would be required to equal the explosive power of 1 mole of
ammonium nitrate? (Another opportunity to practice what “per mole” means.)