Physics Ch. 12 Thermal Energy
Entropy is the amount of work done in the absence of friction.
F
In a gas kept at a constant temperature, all molecules move with the same speed.
F
In a vacuum flask, the vacuum helps in reducing heat loss due to radiation.
F
A man has a metabolic rate of 150 W when he is working on a computer. Assuming he has a normal body temperature of 37C, calculate the rate at which his entropy is changing.
-0.48 J/K•s
On the Celsius scale, the freezing point of pure water is defined as ____________________.
0 degrees C
A 3.00 10-3-kg lead bullet enters a target with a speed of 2.00 102 m/s and comes to rest within the target. Calculate the rise in temperature of the bullet assuming that 80.0% of the heat produced is absorbed by the bullet. The specific heat of lead is 1.30 102 J/kg K.
123 K
A 0.10-kg copper calorimeter contains 0.15 kg of paraffin at 15.0C. When a 0.050-kg piece of aluminum at 100.0C is dropped into the calorimeter, the final temperature of the mixture is 25.0C. Calculate the specific heat capacity of paraffin. The specific heat capacities of aluminum and copper are 1.0 103 J/kg K and 4.0 102 J/kg K respectively.
2.2 x 10^3 J/kg•K
A 0.200-kg piece of lead at 100.0C is dropped into a calorimeter. The calorimeter is a copper can of mass 5.00 10-2 kg and already contains 0.100 kg of water at 20.0C. Calculate the final temperature if the specific heats of water, lead, and copper are 4.20 103 J/kg K, 1.30 102 J/kg K, and 4.00 102 J/kg K respectively.
24.5 °C
Calculate the change in entropy of 0.020 kg of ice when it melts at 0.0C. The heat of fusion of ice is 3.36 105 J/kg.
25 J/K
To melt 4 kg of a solid, 106 J of heat is required. Which of the following expressions gives the heat of fusion of the solid?
C. 10^6/4 J/kg
The normal atmospheric boiling point of water is ____________________ Kelvin.
373
How much heat must be removed from 0.15 kg of water to cool it from 95C to 25C? The specific heat capacity of water is 4182 J/kg K.
4.4 x 10^4 J
A heat engine operates between a high-temperature source and a low-temperature sink. It takes 200 J from the source and delivers 120 J to the sink. What is the efficiency of the heat engine?
40%
The temperature of a 2-kg metal block rises by 10 deg. C when 8000 J is supplied to it. What is the specific heat of the metal?
400 J/kg•°C
Convert 173C to kelvins.
446 K
The temperature of a 0.0020-kg of fusion of bullet is 0.0C. The material of the bullet has a specific heat of 840 J/kg K and a heat of fusion of 6.3 104 J/kg. What is the minimum velocity with which the bullet should be fired for it to melt completely when suddenly brought to rest? The bullet melts at 400.0C. Assume that the kinetic energy is completely converted to heat and there is no loss of heat.
890 m/s
A 0.050-kg copper calorimeter contains 0.050 kg of ice at -10.0C. What mass of steam at 100.0C is required to convert the ice to water at 30.0C?
9.8 x 10^-3 kg
Explain why the air that comes out of a burst tire is cooler than the surrounding air.
A tire burst is a sudden change and there is not much heat transfer. The expanding air does positive work. According to the first law of thermodynamics, this work causes an equal decrease in internal energy. The decrease in internal energy relates to a decrease in the average kinetic energy of the molecules and, therefore, the temperature.
A block of copper (specific heat = 385 J/kg•K) requires 635,000 J of thermal energy to change in temperature from 17C to 139C. What is the mass of this copper block?
A. 13.5 kg
How much thermal energy is required to completely melt 10.6 kg of ice at its melting point?
A. 3.54 x 10^6 J
A 2.15 kg block of aluminum (specific heat = 897 J/kg•K) is at an initial temperature of 300 K. What will its final temperature be if 335,000 J of thermal energy are added?
A. 474 K
5000 J of heat is supplied in one minute to 0.06 kg of a liquid at its boiling point of 85°C to convert it completely to vapor. Which of the following expressions gives the heat of vaporization of the liquid?
A. 5000/0.06 J/kg
How much thermal energy is released when 2.75 kg of steam is completely condensed?
A. 6.22 x 10^6 J
Which is the transfer of thermal energy through direct contact of particles?
A. Conduction
What happens when water at its melting point solidifies to ice without any change in temperature?
A. Latent heat is emitted.
Which of the following physical properties can be used to measure temperature using a thermometer?
A. Volume
Which is an example of heating through convection?
A. warm air rising toward the ceiling
Mechanical energy can be converted to thermal energy through friction, but the reverse never occurs.
F
Compare the behavior of solids and gases on the particle level as these substances heat up.
As an object heats up, its particles have an increased amount of kinetic and potential energies. Particles in solids remain connected to one another, as if by springs. Their increased energy results in an increased vibration of these particles between one and another. Gases, however, are only loosely connected to one another and are free to move. Increased heat results in these particles gaining kinetic energy that causes them to both move faster and collide more frequently. This results in larger changes in volume for gases as temperatures change.
A total of 95,000 J of thermal energy are added to 2.81 kg of lead (specific heat = 130 J/kg•K) to reach a final temperature of 642 K. What was the initial temperature of the lead?
B. 382 K
How much thermal energy is required to completely boil 2.83 kg of water from an initial temperature of 50C?
B. 6.99 x 10^6 J
Heat is added to an open container of a liquid. The liquid is brought to its boiling point and half the liquid boils away. Which of the following graphs shows how the temperature changes with time in this period?
B. Temp rises to a certain point then remains constant
When a closed tin is heated, the pressure inside it increases. This happens because:
B. The molecules move faster and each molecule strikes the walls of the tin more often.
A 50.0 g ice cube is at its melting point. How much thermal energy is absorbed for it to become water at room temperature (17C)?
C. 2.03 x 10^4 J
Which is an example of heating through conduction?
B. touching a hot stove
The temperature at which a liquid changes into a gas is called the ____________________.
Boiling point
Which is not a correct temperature equivalent?
C. 289 deg. C = 552 K
The melting point of a solid is 90.0C. What is the heat required to change 2.5 kg of this solid at 40.0C to a liquid? The specific heat of the solid is 390 J/kg K and its heat of fusion is 4000 J/kg.
C. 5.9 x 10^4 J
Which is the transfer of thermal energy through the motion of particles caused by temperature differences?
C. Convection
A solid is heated at a constant rate until it reaches the vapor state. The temperature of the substance changes with time as shown in the graph below. Which part(s) of the graph indicate(s) that the substance exists in solid-liquid and liquid-vapor state?
C. PQ (which is flat), and RS (which is flat)
Which type of change requires more energy for the same substance?
C. Vaporizing into gas
The total amount of thermal energy is constant in a ____________________.
Closed system
A hot object has more thermal energy than a similar cold object only because of greater kinetic energy.
F
Absolute zero is defined as the zero point on the Celsius scale.
F
The specific heat of copper is 385 J/kg•K. If a 2.6 kg block of copper is heated from 300 K to 450 K, how much thermal energy is absorbed?
D. 150,000 J
50 g of ice at 0°C is dropped in a beaker containing 100 g of water at 0°C. What will be the contents of the beaker after 5 hours? Assume that the room temperature is 0°C.
D. 50 g of ice and 100 g of water
What is the specific heat of a substance that requires 99,100 J of thermal energy to heat 3.47 kg of this substance from 11C to 45C?
D. 840 J/kg•K
Which is not associated with an increase in entropy?
D. A more orderly arrangement of particles
The ratio of useful work produced compared to the amount of input heat is referred to as____________________.
Efficiency
Compare and contrast warm-blooded animals (endotherms) with cold-blooded animals (ectotherms).
Endotherms regulate their body temperature by changing their metabolic rate to maintain a constant internal temperature. Ectotherms' internal temperatures change to reflect the temperature of their environment.
The measure of disorder in a system is called ____________________.
Entropy
A heat pump works because it does not have to obey the second law of thermodynamics.
F
Some machines can accomplish work with no increase in entropy because they have no friction associated with them.
F
The amount of thermal energy transferred between objects depends only on their masses and initial and final temperatures.
F
The temperature of a bottle containing water rises when it is shaken vigorously since shaking adds heat to the system.
F
The temperature of a system must increase when heat energy is added.
F
The thermal energy of the particles in a gas is related to the temperature of the gas.
F
Thermal equilibrium is the point at which no more thermal energy is transferred between objects.
F
When the same amount of thermal energy is added to both an object with high specific heat and an object with low specific heat, the object with a high specific heat will increase in temperature more than the object with a low specific heat.
F
The ____________________ law of thermodynamics explains that energy cannot be created or destroyed.
First
The amount of energy required to melt a solid depends on its mass and its ____________________.
Heat of fusion
The amount of energy required to vaporize a liquid depends on its mass and its____________________.
Heat of vaporization
Explain why the heat of vaporization is greater than the heat of fusion for most substances.
It requires more energy to vaporize a liquid at its boiling point because the particles have to overcome additional forces attracting particles to one another in order for the particles to vaporize. Melting a solid does not take as much energy because although the particles are no longer in a regular arrangement as in the solid phase, they have more forces holding them in the liquid phase.
James places a 100 g block of copper at 50 deg. C next to a 100 g block of silver at 20 deg. C. He asserts that at thermal equilibrium, the final temperatures of both blocks of metal will be 35 deg. C. Do you agree with James? Explain why or why not.
James is incorrect. The final temperature depends on the specific heat of the each substance. Since the silver has a lower specific heat, it will change in temperature more than the copper as thermal energy is exchanged.
During heating, added thermal energy is used to increase the motion or ____________________ of particles.
Kinetic energy
Four identical insulated containers hold equal masses of different liquids at 0°C. Identical immersion heaters supply heat at the same rate to all liquids. The specific heats and the boiling points of the liquids are provided below. Which liquid will boil first?
Liquid C will boil first.
The temperature at which a substance changes from a solid into a liquid is called the ____________________.
Melting point
When heat is transferred out of an object, the sign of its value for Q is____________________.
Negative
Propose an experimental design that would allow you to determine the identity of an unknown metal using thermodynamics concepts.
One could use specific heat to identify a metal by using calorimetry to determine the specific heat of the metal and looking up the specific heat value in a data table. The metal should be heated to a known initial temperature, perhaps by immersing it in boiling water for approximately 5-10 minutes. It can then be placed into a known mass of water at a known initial temperature in a well-insulated container. The final temperature of the water should be determined after the system reaches thermal equilibrium. The change in thermal energy of the water will be equal to the thermal energy change of the metal; the sum of the two thermal energies will be zero, allowing one to calculate the specific heat value of the metal.
A piece of copper (specific heat = 385 J/kg•K) has a mass of 275 g. If it is heated to 145C, then plunged into 5.00 kg water (specific heat = 4180 J/kg•K) at 20C, what will be the final temperature at equilibrium?
Qa + Qb = 0 Tf = 20.6°C
The ____________________ law of thermodynamics explains that the amount of entropy in a system tends to increase.
Second
Find the amount of energy required to change a 4.50 kg block of ice at the temperature, shown by point a on the graph, to a liquid at the temperature shown by point d on the graph.
Step 1: Q = mC(Tf - Ti); Q = (4.50 kg)(2060 J/kg•K)(273-150) = 1140210 J Step 2: Q = mHf = (4.50 kg)(3.34 x 10^5 J/kg) = 1,503,000 J Step 3: Q = mC(Tf - Ti); Q = (4.50 kg)(4180 J/kg•K)(320-273) = 884,070 J Total = 3,527,280 = 3.53 x 10^6 J
Find the amount of energy required to change a 4.50 kg block of ice just at its melting point to a gas at the temperature shown by point g on the graph.
Step 1: Q = mHf = (4.50 kg)(3.34 x 10^5 J/kg) = 1,503,000 J Step 2: Q = mC(Tf - Ti); Q = (4.50 kg)(4180 J/kg•K)(373-273) = 1,881,000 J Step 3: Q = mHf = (4.50 kg)(2.26 x 10^6 J/kg) = 10170000 J Step 4: Q = mC(Tf - Ti); Q = (4.50 kg)(2020 J/kg•K)(500-373) = 1,154,430 J Total = 13,205,430 = 1.32 x 10^7 J
A machine can never be 100 percent efficient because some energy is lost as waste heat.
T
An insulated cooler has held a mixture of ice and water all day. The temperature of the water and the temperature of the ice are therefore the same.
T
During melting or vaporization, particles increase in potential energy but not in kinetic energy.
T
In thermodynamics terms, a sink is where the thermal energy is deposited.
T
It is not possible to have a process in which the entropy of an isolated system decreases.
T
Refrigerators work because the heat flows spontaneously from warmer food to the colder air inside the refrigerator.
T
The entropy of a system measures the state of disorder of the system.
T
The magnitude of one degree Celsius is the same as one Kelvin.
T
The volume of a gaseous system increases when it does positive work in a thermodynamic process.
T
Thermal equilibrium occurs when two objects have the same temperature.
T
When heat flows into an object, its temperature and thermal energy increase.
T
James states that the Second Law of Thermodynamics is violated when plants grow, because the mature plant is more organized. Do you agree with James? Explain your response.
The Second Law of Thermodynamics is not violated. It applies to a closed system, and in the case of a plant growing, one needs to take into account the energy input from the Sun.
What is the change in the internal energy of a gaseous system in a cyclic process?
The internal energy does not change in a cyclic process.
A fixed mass of a gas at a temperature T is present in a container. Exactly half the molecules of the gas are removed from the container without changing the average kinetic energy per molecule of the gas within the container. What is the temperature of the gas still in the container?
The temperature of the gas in the container is T.
Explain how a refrigerator can continue to keep food cold if warmer food continues to be added to it.
Thermal energy flows spontaneously to the air in the refrigerator from the warmer food, cooling the food down. In order to keep the air in the refrigerator cold, energy must be removed from it. Pipes circulate in the refrigerator and contain a liquid that is vaporized as thermal energy is removed from the inside of the refrigerator. The gas passes through a condenser where thermal energy is removed from the gas, converting it to a liquid, and releasing the thermal energy to the air outside the refrigerator.
The point at which the net flow of thermal energy between two objects at the same temperature is zero is called ____________________.
Thermal equilibrium
The study of heat transformations into other forms of energy is called____________________.
Thermodynamics
Explain why the heat of fusion and heat of vaporization do not depend on a substance's temperature.
These do not depend on temperature because they occur at a set temperature, either the melting point or boiling point respectively.
Heat tends to flow from the ____________________ object to the ____________________ object.
Warmer, colder
0.2000 kg of water at 20.00C is contained in a 0.1000-kg copper container. The container is shaken vigorously for 10.00 minutes to cause the temperature to rise to 22.00C. Calculate the work done on the system and the heat supplied to the system. The specific heat of copper is 385.0 J/kg K and of water is 4200.0 J/kg K.
Work done = 1757 J Heat supplied = 0
A gas is kept in a rigid container and 100 J of heat is supplied to it. What is the work done by the gas and the change in the internal energy of the gas?
Work done by the gas = 0 J Change in internal energy = -100 J
