Chapter 8: Temperature and Heat

MR. SURRETTE VAN NUYS HIGH SCHOOL

CHAPTER 8: TEMPERATURE AND HEAT HEAT AND THERMODYNAMICS WORKSHEET 4 Equations: H = kAT/L, Ug = mgh, Qc = mcT, P = AeT , QL = mL, U = Q – W,

W = PV, S = Q/T, p1V1/T1 = p2V2/T2, e = (QH – QC)/QH, Q = QC + QL, V = Vf - Vi Conversion: 1 cal = 4.186 J

1. A silver bar of length 24 cm and cross-sectional area 1 cm2 is used to transfer heat from a 115oC reservoir to a - o o 20 C reservoir. How much heat is transferred per second? (kSILVER = 427 W/m C) [ANS: 24.0 W]

2. A 3.4 gram copper penny at 18oC is dropped from a height of 215 m and strikes the ground. If 45% of the energy goes into increasing the internal energy of the coin, determine its final temperature. (The specific heat of copper is 387 J.kg.oC) [ANS: 20.5oC]

3. A solar heating system has a 33% conversion efficiency; the solar radiant incident on the panels is 560 W/m2. What is the increase in temperature of 42 kg of water in a one hour period by a 4.0 m2 area collector? (The specific heat of water is 4186 J.kg.oC) [ANS: 15.1oC]

4. If the absolute temperature of a spherical object were doubled, by what factor would the rate of radiated energy emitted from its surface be changed? [ANS: 16x]

5. A 1.2 kg block of copper at 10oC is dropped into a large vessel of liquid nitrogen at 72 K. How many kilograms of nitrogen boil away by the point the copper reaches 72 K? (The specific heat of copper is 385 J/kg.oC. The heat of vaporization of nitrogen is 2 x 105 J/kg.) [ANS: 0.49 kg]

6. How much heat energy is required to melt a 35 gram block of silver at 41oC? The melting point of silver is 960o C, its specific heat is 2.34 x 102 J/kg.oC, and its heat of fusion is 8.83 x 104 J/kg. [ANS: 1.06 x 104 J]

7. An ideal gas undergoes an adiabatic process (no heat exchange with the environment) in doing 32 J of work on its environment. What is its change in internal energy? [ANS: - 32 J]

8. An ideal gas is maintained at an average pressure of 200 N/m2 during an isobaric process while its volume decreases by 0.2 m3. What work is done by the system on its environment? [ANS: - 40 J]

9. A boulder of mass 600 kg tumbles down a mountainside and stops 160 m below. If the temperature of the boulder, mountain, and surrounding air are all at 300 K, what is the change in entropy of the Universe? [ANS: 3136 J/K]

10. A bottle containing an ideal gas has a volume of 2.5 m3 and a pressure of 1 x 105 N/m2 at a temperature of 255 K. The bottle is placed against a metal block that is maintained at 950 K and the gas expands as the pressure remains constant until the temperature of the gas reaches 950 K. How much work is done by the gas? [ANS: 6.8 x 105 J]

11. A gasoline engine absorbs 2750 J of heat energy and performs 800 J of mechanical work in each cycle. What is the efficiency of the engine? [ANS: 29.1%]

12. Calculate the entropy change when 6 mol (108 grams) of water at 100oC is converted into steam (The heat of vaporization of water is 540 cal/g). [ANS: 654.5 J/K]

PHYSICS SCIENCE DEPARTMENT MR. SURRETTE VAN NUYS HIGH SCHOOL

CHAPTER 8: TEMPERATURE AND HEAT TEMPERATURE AND GAS LAWS WORKSHEET

Equations: Y = (F/A) / (L/Lo), V = VoT, pV = nRT, (p1V1)/T1 = (p2V2)/T2, L = LoT, 1/2 TF = 9/5 TC + 32, vrms = (3RT/M) , L = LoT -3 3 23 Conversions: 1 L = 1 x 10 m , 1 mol = 22.4 L, NA = 6.02 x 10 / mol

1. Consider two containers that have the same volume and temperature. The first contains a certain number of oxygen molecules while the second contains the same number of hydrogen molecules. Which container has the greatest pressure? [ANS: same pressure]

2. Suppose for a brief moment that the gas molecules hitting a wall stuck to the wall instead of bouncing off the wall. How would the pressure on the wall be affected during that brief time? [ANS: ½ pressure]

3. Four moles of an ideal gas are confined to a 25 liter container at a pressure of 3 atmospheres. What is the gas temperature? (R = 0.0821 L.atm/mole.K) [ANS: 228.4 K]

4. Suppose one sphere is made of a metal that has three times the coefficient of linear expansion of a second sphere. The coefficient of volume expansion for the first sphere will be bigger than the second by a factor of what number? [ANS: 3x]

5. Suppose the ends of a 30-m-long steel rail are rigidly clamped at 0o C to prevent expansion. The rail has a cross-sectional area of 30 cm2. What force does the rail exert when it is heated to 40o C? -5 o 11 2 5 (steel = 1.1 x 10 / C, Ysteel = 2 x 10 N/m ) [ANS: 2.64 x 10 N]

6. An unknown gas condenses into a liquid at approximately 150o Kelvin. What temperature is this in degrees Fahrenheit? [ANS: - 189.4o F]

7. An auditorium has dimensions 10 m x 20 m x 30 m. How many molecules of air are needed to fill the auditorium at standard temperature and pressure? [ANS: 1.61 x 1029 molecules]

8. A helium-filled balloon has a volume of 1 m3. As it rises in the Earth’s atmosphere, its volume expands. What will be its new volume (in cubic meters) if its original temperature and pressure are 20oC and 1 atm, and its final temperature and pressure are – 40oC and 0.1 atm? [ANS: 7.95 m3]

9. If the rms velocity of a helium atom at room temperature is 1350 m/s, what is the rms velocity of an unknown (X) molecule (mass of X = 64 grams, mass of He = 4 grams)? [ANS: 337.5 m/s]

PHYSICS SCIENCE DEPARTMENT