1) It is said that the combustion of hydrogen or natural gas produces less emissions than the
combustion of gasoline or oil related to the same energy generated by either fuel. Check this
statement quantitatively
Data: heat of combustion of H2 is about 240 kJ/mol, CH4 803 kJ/mol and C8H18 5090 kJ/mol
(reaction heats depend on temperature!)
2) The area of forests on Earth is 4.5·107 km2. In 1860 it was still 6·107 km2.
a) How much carbon of the atmosphere would be fixed per year if the lost area would be
afforested? Assume that the amount of carbon fixed as CO2 by photosynthesis is 500 t per year
and km2 provided the forest is in the growing state.
b) Today the amount of carbon emitted as CO2 by combustion of fossil fuels and wood is
2.7·1010 t per year. What is the increase (in %) of carbon per year if the total amount of carbon
(C) in the atmosphere is 8.1·1014 kg? Assume that half of the emitted carbon is fixed as CO2 by
absorption in the oceans.
c) How much is the netto emission of carbon in the atmosphere if the reforestation program
mentioned above would be realized? What is the reduction of emitted carbon in % per year in
this case?
3) Coal used for combustion in a 300 MW power plant has the following chemical composition
(in weight %):
82% carbon; 6,5% inert solids; 5% hydrogen; 5% water; 1.5% sulfur
a) The heat content of coal is 29 kJ/g. How much coal has to be fired per hour if the electrical
efficiency of the power plant is 40%?
b) What is the composition (as molar fractions) of the exhaust gas if we assume that all oxygen
of the air is consumed to burn the coal?
c) The allowed limiting concentration of SO2 in the air according to WHO is 350 μg/m3, in the
exhaust gas it is about 500 mg/m3. How much SO2 (in %) has to be removed by a suitable
desulfuration procedure before the exhaust gas enters the atmosphere?
4) Concentration of perchloroethylene (PCE) in the industrial zone is measured at 5 ppmv
(cm3/m3) – sampling 1 m above the surface. Waste was probably treated illegally in this area in
the past. Analysis of surface soil leads to PCE concentration at 50 ppb (μg/kg). Is the soil-bound
PCE the source of PCE in the air?
5) A gasoline tank of a car contains 50 l. Every time the empty tank is refilled, gaseous gasoline
is pressed out of the tank and released to the air. Assume that the partial pressure of gasoline in
the empty tank is equal to the saturated vapor pressure of liquid gasoline. The assumption is
justified by the fact that even in the empty tank there is a small amount of liquid gasoline left
being in equilibrium with gaseous gasoline.
a) Calculate the amount of gaseous gasoline emitted to the air when the empty tank is refilled.
The vapor pressure of gasoline at 300 K is 7 kPa, the average molar mass of gasoline is about
100 g/mol.
b) There are over 4 million private cars in the Czech Republic (all cars about 6.5 million).
Assume that each of them drives 20 000 km per year consuming 8 l of liquid gasoline per 100
km (averaged figures). How much gasoline is emitted into the air by losses due to refilling all the
tanks? What volume of liquid gasoline corresponds to this loss? The density of liquid gasoline is
0.68 g/cm3.
6) 90 ml of NO2 dissolves in 100 g of water at 20°C and at atmospheric pressure. Evaluate the
Henry’s law constant of NO2 if the saturated vapor pressure of water at this temperature is 2.3
kPa and the gas phase contains only NO2 and water vapor.
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