Hw 9: Thermal Physics 9.1) a) An ideal gas occupies a volume of 1.0cm3 at 20C and atmospheric pressure.Determine the number of molecules of gas in the container.[2.5 1019 molecules] b) If the pressure of the 1.0cm3 volume is reduced to 1.01011 P a (an extremely good vacuum) while the temperature remains constant, how many moles of gas remain in the container?[4.1 1021 mol]

9.2) A weather balloon is designed to expand to a maximum radius of 20 m at its working altitude, where the air pressure is 0.030 atm and the tempera- ture is 200 K. If the balloon is filled at atmospheric pressure and temperature of 300 K, what is its radius at liftoff?[7.1 m]

9.3) A 75 g ice cube at 0C is heated until 45g has become water at 0C. How much energy was added to accomplish the transformation?[1.50 104 J]

9.4) A student drops two metallic objects into a 120 g steel container holding 150 g of water at 25C. One object is a 200 g cube of copper that is initially at 85C, and the other is a chunk of aluminum that is initially at 5.0C. To the surprise of the student, the water reaches a final temperature of 25C, precisely where it started. What is the mass of the aluminum chunk?[0.26 kg]