Cloud formation Air consists mostly of nitrogen (N2), with a molecular mass of 28, a...

Cloud formation Air consists mostly of nitrogen (N₂), with a molecular mass of 28, and oxygen (O₂), with a molecular mass of 32. A water molecule (H₂O) has molecular mass 18. According to the ideal gas law (N/V = P/kT), dry air at a particular pressure and temperature has the same particle density (number of particles per unit volume) as humid air at the same pressure and temperature. Consequently, humid air, whose low-mass water molecules replace more massive nitrogen and oxygen molecules, is less dense than dry air—the humid air rises. Atmospheric pressure decreases with elevation since there is less air above that is pushing down. At about 5000 m above the Earth’s surface, the pressure is about 0.5 atm. Assuming an ideal gas, the gas volume V increases as pressure P decreases. What happens to the air temperature as humid air rises? Air is a poor thermal energy conductor, and there is little heating from neighboring air (Q = 0, an adiabatic expansion process). As the rising gas expands, the neighboring environmental gas pushes in the opposite direction of the increasing volume of this rising gas. The environment does negative work on the rising air system (W _{by Environment on System} < 0). According to the first law of thermodynamics The system’s internal thermal energy decreases with a corresponding temperature decrease—about -10 °C for each 1000-m increase in altitude. When the humid air reaches its dew point temperature, it starts to condense into water droplets (cloud formation). When condensation occurs, energy is released. There is a competition between decreasing thermal energy as the air expands and increasing thermal energy as the water vapor condenses. The air now cools at a lower rate of about -5 °C for each 1000-m increase in elevation. Meteorite impact The great Arizona crater was created by the impact of a meteorite of estimated 5 * 108 kg mass. The meteorite’s speed before impact was about 10,000 m>s. Large amounts of rock found near the crater appeared to have melted on impact and then solidified as it cooled, indicating that the temperature of the rock during impact reached at least 1700 _C, the melting temperature of the rock. Is this possible? Consider Earth and the meteorite as the system. The initial state of the process is the meteorite moving fast just before hitting Earth’s surface. The final state is several minutes after the collision. What types of energy transformation occurred? The meteorite had kinetic energy before impact. In the collision, the meteorite dug a hole in Earth, forming the crater. The displaced soil was raised a distance approximately equal to the diameter of the meteorite. This inelastic collision produced considerable internal energy— thermal energy of the meteorite and of Earth’s surface matter at the collision site. If the temperature change was high enough, the meteorite and/or parts of Earth may have undergone one or more phase changes. We summarize the process as follows:

Ki = ΔUgf + ΔU_thermal

In the following questions, estimate different energies and energy changes. In addition to the information already given, you can use the following: 3300 kg/m³ meteorite density; 840 J/kg . °C specific heat for the solid meteorite; 2.7 X 10⁵ J/kg heat of fusion, the same as that of iron; 1000 J/kg . °C specific heat for the liquid meteorite, the same as that of iron; and 6.4 X 10⁶ J/kg heat of vaporization, the same as for iron.

The energy needed to vaporize the melted meteorite at its 2600 °C boiling temperature is closest to