A particular refrigerator cools by evaporating liquefied dichlorodifluoromethane, CCl2F2. How many kilograms of this liquid must be evaporated to freeze a tray of water at 0°C to ice at 0°C? The mass of the water is 505 g, the heat of fusion of ice is 6.01 kJ/mol, and the heat of vaporization of dichlorodifluoromethane is 17.4 kJ/mol.

A 0.250-g chunk of sodium metal is cautiously dropped into a mixture of 50.0 g water and 50.0 g ice, both at 0C. The reaction is 2Na(s)+2H2O(l)2NaOH(aq)+H2(g)H=368kJ Assuming no heat loss to the surroundings, will the ice melt? Assuming the final mixture has a specific heat capacity of 4.18 J/gc, calculate the final temperature. The enthalpy of fusion for ice is 6.02 kJ/mol.

Why are steam burns so much worse than water burns even if the H2O is at the same temperature for both phases? Hint: Consider the heat of vaporization of water.

Are changes in state physical or chemical changes? Explain. What type of forces must be overcome to melt or vaporize a substance (are these forces intramolecular or intermolecular)? Define the molar heat of fusion and molar heat of vaporization. Why is the molar heat of vaporization of water so much larger than its molar heat of fusion? Why does the boiling point of a liquid vary with altitude?

Diethyl ether (CH3CH2OCH2CH3) was one of the first chemicals used as an anesthetic. At 34.6C, diethyl ether has a vapor pressure of 760. torr, and at 17.9C, it has a vapor pressure of 400. torr. What is the H of vaporization for diethyl ether?

Which would you expect to have the higher fusion enthalpy, N2 or I2? Explain your choice.

A 1.50-g sample of methanol (CH3OH) is placed in an evacuated 1.00-L container at 30 C. (a) Calculate the pressure in the container if all of the methanol is vaporized. (Assume the ideal gas law, PV = nRT.) (b) The vapor pressure of methanol at 30 C is 158 torr. What mass of methanol actually evaporates? Is liquid in equilibrium with vapor in the vessel?

The enthalpy of vaporization of water is larger than its enthalpy of fusion. Explain why.

Use Figure 11.7 to estimate the boiling point of carbon tetrachloride, CCl4, under an external pressure of 250 mmHg.

Decide which substance in each of the following pairs has the lower melting point. Explain how you made each choice. a potassium chloride, KCl; or calcium oxide, CaO b carbon tetrachloride, or hexachloroethane, c zinc, Zn; or chromium, Cr d acetic acid, CH3COOH; or ethyl chloride, C2H5Cl