Which of the following pure substances has the lowest

21. Which of the following pure substances has the lowest melting point?
A) NaF B) LiF C) CsF D) RbF E) KF
22. For an ideal gas, which of the following statements is true? 23. The density of a gas is 3.17 g/L at STP. What is its molar mass?
24. The volume of a sample of gas measured at 10.0°C and 1.00 atm pressure is 9.00 L. What must the final
temperature be in order for the gas to have a final volume of 6.00 L at 1.00 atm pressure?

25. A particular compound has an enthalpy of vaporization of 28100 J/mol. At 276 K it has a vapor pressure
of 103 mmHg. What is its vapor pressure at 304 K? ( R = 8.31 J/(K· mol))
A) 99.9 mmHg D) 106 mmHg
B) 318 mmHg E) 33.3 mmHg
C) 171 mmHg
26. For a particular liquid, raising its temperature from 335 K to 353 K causes its vapor pressure to double.
What is the enthalpy of vaporization of this liquid? ( R = 8.31 J/(K· mol))
27. How much heat is released at constant pressure if a 13.0-L tank containing 40.0 atm of hydrogen sulfide
gas condenses at its boiling point of -60.0 o C? The enthalpy of vaporization of hydrogen sulfide is 18.7
kJ/mol at -60.0 o C. ( R = 0.0821 L • atm/(K • mol))
J
J
28. The normal boiling point of a liquid is