Chapter 23 review

    Quantitative problems
      Section 23.1
      1. Medium Yesterday it was 20ºC outside. Today, it is 25ºC.
        1. How much higher, in kelvins, is the temperature today than it was yesterday?
        2. How much higher is the temperature in degrees Fahrenheit?

      2. Medium In a balloon at room temperature (25ºC), how much thermal energy does the average helium atom have?

      3. Medium Alonzo puts 2 kg of 20ºC water [specific heat cp = 4,184 J/(kg ºC)] on the stove. The stove provides 502,080 J of thermal energy to the water. What is the maximum temperature that the water can be heated to by this energy?

      4. Medium Hugh heats 10 kg of aluminum (ask your teacher for the specific heat if you do not remember it) from 15ºC to 55ºC. What is the least amount of work he could have done to heat it?

      5. Challenging A hot, 100-g glass prism is placed in an insulated 300-mL sample of water at room temperature (22°C), causing the temperature of the water to come to equilibrium at 25°C. What was the initial temperature of the hot glass prism? [The specific heat of glass, cp,g, is 664 J/(kg °C).]

      6. Challenging Amelia performs an experiment to determine the type of an unknown metal. She places a 0.10 kg block of the metal at 25ºC into 1.0 kg of 75ºC water. After stirring for a few minutes she measures the temperature of both the water and metal to be 74.54ºC.
        1. The specific heat of water is 4,184 J/(kg ºC). How much thermal energy did the water lose in going from 75ºC to 74.54ºC?
        2. How much thermal energy did the metal gain in going from 25ºC to 74.54ºC?
        3. What is the specific heat of the unknown metal?
        4. The specific heats of aluminum, copper, and lead are 900, 386, and 128 J/(kg ºC), respectively. Which of these three metals is the unknown metal?
        5. Explain in detail what Amelia should do if her experimental value for the specific heat doesn’t correspond with any of the given values.

      Section 23.2
      1. Easy Suppose that a typical compact car’s gas tank has a capacity of 13 gallons. When the tank is full, how much mass and weight does fuel add to the car? (Express the fuel weight in both newtons and pounds). The density of gasoline is about 740 kg/m3. Use the conversion factors 1 m3 = 1,000 liters (L), 1 gal = 3.78 L, and 1 lb = 4.45 N.

      1. Easy For the following questions, consider an ideal gas that is currently at a temperature of 27°C.
        1. If the gas is heated by 1°C while the pressure is held constant, by what fraction will its volume change?
        2. If the volume is held fixed while the gas is cooled by 1°C from 27°C, by what fraction will its pressure change?
        3. If the temperature of the gas is held constant while its volume is expanded by 1%, by how much will its pressure change?

      2. Medium Car tires are typically inflated to a pressure of roughly 35 psi (pounds per square inch). Perform the following calculations with a precision of three significant figures.
        1. Convert this pressure into a number of pascals by using the following conversion factors and definitions: 1 in = 2.54 cm, 1 cm = 0.01 m, 1 lb = 4.45 N, and 1 Pa = 1 N/m2.
        2. Assuming that a compact car’s mass is 1,200 kg, calculate the weight supported by each of its four tires (in newtons).
        3. Divide the force from Part b by the pressure from Part a to get an area in square meters. Also express this area in square inches.
        4. What is the physical significance of this area?

      Section 23.3
      1. What is the thermal energy per atom for argon gas at room temperature (68°C)?

      2. A car tire has a volume of 10 L and is inflated to a gauge pressure of 30 psi (207,000 Pa) at 20°C. How many air molecules are there inside the tire?

      3. Medium A midsize airship (blimp) contains roughly 200,000 ft3 of helium gas at an approximate pressure of 1.1 atmospheres. 1 ft3 = 0.0283 m3 and one atmosphere of pressure = 1.01×105 N/m2.
        1. Suppose a blimp’s helium is at 12°C (around 54°F). How many moles of helium does the blimp contain?
        2. What is the mass of this quantity of helium? (Helium has a molar mass of 16.0 g/mol.) Compare this to the mass of a compact car (about 1,200 kg).
        3. Imagine that this helium could cool by 1°C at constant volume. How much energy would this liberate? Compare this quantity to one kilowatt-hour. (1 kWh = 3.6×106 J.)
        4. What is the average thermal speed of a helium atom at 12°C? Compare this to a typical highway speed (30 m/s, or about 66 mph).

      694 Previous Page Next Page