Question

The emission of NO2 by fossil fuel combustion can be prevented by injecting gaseous urea into the combustion mixture. The urea reduces NO (which oxidizes in air to form NO2) according to the following reaction:
2CO(NH2)2(g)+4NO(g)+O2(g)→4N2(g)+2CO2(g)+4H2O(g)
Suppose that the exhaust stream of an automobile has a flow rate of 2.42 L/s at 661 K and contains a partial pressure of NO of 14.0 torr

Answer 1

Answer on Question #81516 – Chemistry – General Chemistry

The emission of $\mathrm{NO}_2$ by fossil fuel combustion can be prevented by injecting gaseous urea into the combustion mixture. The urea reduces NO (which oxidizes in air to form $\mathrm{NO}_2$) according to the following reaction:

$$2 \mathrm{CO}(\mathrm{NH}_2)_{2(\mathrm{g})} + 4 \mathrm{NO}(\mathrm{g}) + \mathrm{O}_{2(\mathrm{g})} \rightarrow 4 \mathrm{N}_{2(\mathrm{g})} + 2 \mathrm{CO}_{2(\mathrm{g})} + 4 \mathrm{H}_2\mathrm{O}(\mathrm{g})$$

Suppose that the exhaust stream of an automobile has a flow rate of 2.42 L/s at 661 K and contains a partial pressure of NO of 14.0 torr.

What total mass of urea is necessary to react completely with the NO formed during 9.0 hours of driving?

Solution:

- 9.0 hours × 3600 seconds / hour = 32400 seconds

- 32400 seconds × 2.42 L/s = 78 408 Litres of NO

Find the moles of NO using the ideal gas law:

$$\mathrm{PV} = \mathrm{nRT}$$ $$(14 \text{ Torr}) \times (78 \text{ 408 Litres}) = \mathrm{n} \times (62.36 \text{ L-Torr/mol} \cdot \mathrm{K}) \times (661 \text{ K})$$ $$\mathrm{n} = 26.63 \text{ moles of NO}$$

According to the equation

$$2 \mathrm{CO}(\mathrm{NH}_2)_{2(\mathrm{g})} + 4 \mathrm{NO}(\mathrm{g}) + \mathrm{O}_{2(\mathrm{g})} \rightarrow 4 \mathrm{N}_{2(\mathrm{g})} + 2 \mathrm{CO}_{2(\mathrm{g})} + 4 \mathrm{H}_2\mathrm{O}(\mathrm{g})$$

- 4 moles of NO reacts with 2 moles of urea,

which, using molar mass, is

$$2 \text{ mol urea} \times 60.06 \text{ g/mol} = 120.12 \text{ grams}$$

so

$$26.63 \text{ moles of NO} \times (120.12 \text{ grams urea}) / (4 \text{ mol NO}) = 800 \text{ grams of urea}$$

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