1. Dry air is roughly 79% N2 and 21% O2 by volume. Calculate its average molar mass and density at STP using the ideal gas law.
2. A mixture containing nitrogen and hydrogen weighs 3.50 g and occupies a volume of 7.46 L at 300 K and 1.00 atm. Calculate the mole fraction and mass percent of these gases. Assume ideal gas behavior.
3. An ideal gas at 300 K is found to exert a pressure of 1.0 bar. What is the pressure exerted by the gas if the temperature is increased to 475K, and the volume of the gas decreases by 10%?
4. A piece of sodium metal reacts completely with water as follows:
2Na(s) + 2H2O (l) → 2NaOH(aq) + H2(g)
The hydrogen gas generated is collected over water at 25.0 °C. The volume of the gas is 246 mL measured at 1.00 atm. Calculate the number of grams of sodium used in the reaction. (Note: vapor pressure of water at 25 °C is 0.0313 atm).
5. Ammonia (NH3) can exist in equilibrium with its component elements, nitrogen (N2) and hydrogen (H2). A sample of ammonia is placed in an evacuated container of fixed volume. (i) If a sample of ammonia is 100% decomposed, and the pressure is found to be 124 torr, what is the partial pressure of each of the gases present? (ii) If the sample of ammonia is only 50% decomposed, and the pressure is found to be 116 torr, what is the partial pressure of each of the gases present?
6. The van der Waals constants a and b for benzene are 18.00 atm L² mol⁻² and 0.115 L mol⁻¹, respectively. Calculate the critical constants (Pc, Vc and Tc) for benzene.
7. Given Pc = 49.3 atm, Vc = 0.0753 L mol-1, and Tc = 151.0 K for argon (Ar), estimate the radius of argon in picometers.
8. Using a P-T phase diagram, describe how to obtain supercritical H2O from ice at STP.