NaCl and KF have the same crystal structure. The only difference between the two is the distance that separates cations and anions.
(a) The lattice energies of NaCl and KF are given in Table 8.1. Based on the lattice energies, would you expect the Na-Cl or the K-F distance to be longer?
(b) Use the ionic radii given in Figure 7.8 to estimate the Na-Cl and K-F distances.
Step 1 of 5) We will determine how each of the quantities in (a)–(e) is affected by the change in volume at constant temperature. Solve (a) Because the average kinetic energy of the O2 molecules is determined only by temperature, this energy is unchanged by the compression. (b) Because the average kinetic energy of the molecules does not change, their average speed remains constant. (c) The number of collisions with the walls per unit time increases because the molecules are moving in a smaller volume but with the same average speed as before. Under these conditions they will strike the walls of the container more frequently. (d) The number of collisions with a unit area of wall per unit time increases because the total number of collisions with the walls per unit time increases and the area of the walls decreases. (e) Although the average force with which the molecules collide with the walls remains constant, the pressure increases because there are more collisions per unit area of wall per unit time.
