Exam 17: Phases and Phase Changes

When a mixture of gases is placed in a container at a given temperature, the pressure in the container is equal to the sum of the pressures that the individual gases would exert if they separately occupied the entire container at the same temperature. Given that air is basically a mixture of nitrogen, with a molecular weight of 28 g/mol, and oxygen, with a molecular weight of 32 g/mol, what must be the ratio of the mass of oxygen to the mass of nitrogen in air for air to have an effective molecular weight of 29?

Using K = 3/2 kT, what is the average kinetic energy of a He atom at: (a) 10. K? (b) -196.°C? (c) 100.°C?

Opposing shearing forces of 3000 N are applied to the 3.00 cm × 4.00 cm faces of a 3.00 cm × 4.00 cm × 5.00 cm steel block. By what amount does the block become slanted? The shear modulus for steel is 8.0 × 10¹⁰ N/m².

A sample of an ideal gas is heated and its Kelvin temperature doubles. What happens to the average speed of the molecules in the sample?

You have had something simmering in a covered pot on the stove and then turn off the heat. Some time later you return to the pot and find that you have trouble lifting the lid. Why?

A container of negligible heat capacity has in it 456 g of ice at -25.0°C. Heat is supplied to the container at the rate of 1000 J/min. How long will it take before the temperature starts to rise above 0°C? The specific heat of ice is 2090 J/(kg K) and the latent heat of fusion of water is 33.5 × 10⁴ J/kg.

A 600-g piece of iron at 100°C is dropped into a calorimeter of negligible heat capacity containing 100 g of ice at 0°C and 120 g of water, also at 0°C. What is the final temperature of the system? The specific heat of iron is 448 J/(kg K) and the latent heat of fusion of water is 33.5 × 10⁴ J/kg.

Steam burns can be much more severe than burns caused by boiling water. The reason for this is that

When a spray can is being used, it feels cooler than when it was first picked up. Why?

When a liquid freezes

If you add 1.33 MJ of heat to 500 g of water at 50°C, what is the final temperature of the steam? The latent heat of vaporization of water is 22.6 × 10⁵ J/kg. The specific heat of steam is 2010 J/(kg K).

A 25-kg television set rests on four rubber pads, each having a height of 1.0 cm and a radius of 0.60 cm. A horizontal force is applied to the television set. When the pads are at the point of sliding, how far has the television set moved sideways? The coefficient of friction between the rubber and the floor is 1.0 and the shear modulus of rubber is 2.6 × 10⁶ N/m².

Explain why, when someone across the room pierces a can of coffee with a can opener, you hear the sound of the can being pierced before you smell the aroma of the coffee.

What is the root mean square value of the following speeds: 2.0 m/s, 3.0 m/s, 4.0 m/s?

A piano wire has a radius of 0.50 mm. One end is fixed and the other is wrapped around a tuning peg, which has a diameter of 3.5 mm and is 80 cm away. After the wire just becomes taut, the peg is given three full turns. What is the tension in the wire? Young's modulus for steel is 20 × 10¹⁰ N/m².

A sample of an ideal gas is slowly compressed to one-half its original volume with no change in temperature. What happens to the average speed of the molecules in the sample?

The melting point of aluminum is 660°C, the latent heat of fusion is 4.00 × 10⁵ J/kg, and its specific heat is 900 J/(kg K). How much heat must be added to 500 g of aluminum at 27°C to completely melt it?

The molecular weight of carbon dioxide is 44.0 g/mol. What is the internal energy in 3.00 kg of carbon dioxide at 300 K? As an approximation, treat the carbon dioxide gas as if it was monatomic.

Opposing shearing forces of 3000 N are applied to the 4.00 cm × 5.00 cm faces of a 3.00 cm × 4.00 cm × 5.00 cm steel block. By what amount does the block become slanted? The shear modulus for steel is 8.10 × 10¹⁰ N/m².

The point in the phase diagram where the vapor pressure curve ends is called the