ConcepTest 16.1 Degrees 1) one Celsius degree 2) one Kelvin degree 3) one Fahrenheit degree 4) both one Celsius degree and one Kelvin degree 5) both one Fahrenheit degree and one Celsius degree Which is the largest unit: one Celsius degree, one Kelvin degree, or one Fahrenheit degree?

ConcepTest 16.1 Degrees 1) one Celsius degree 2) one Kelvin degree 3) one Fahrenheit degree 4) both one Celsius degree and one Kelvin degree 5) both one Fahrenheit degree and one Celsius degree Which is the largest unit: one Celsius degree, one Kelvin degree, or one Fahrenheit degree? The Celsius degree and the Kelvin degree are the same size. The scales only differ by an offset, not by the size of the degree unit. For Fahrenheit, there are 180 degrees between boiling and freezing (212°F–32°F). For Celsius, there are 100 degrees between the same points, so the Celsius (and Kelvin) degrees must be larger.

ConcepTest 16.2 Freezing Cold 1) yes, at 0 °C 2) yes, at -273 °C 3) yes, at 0 K 4) no It turns out that – 40°C is the same temperature as – 40°F. Is there a temperature at which the Kelvin and Celsius scales agree?

ConcepTest 16.2 Freezing Cold 1) yes, at 0 °C 2) yes, at -273 °C 3) yes, at 0 K 4) no It turns out that – 40°C is the same temperature as – 40°F. Is there a temperature at which the Kelvin and Celsius scales agree? The Celsius and Kelvin scales differ only by an offset, which is 273 degrees. Therefore, a temperature on one scale can never match the same numerical value on the other scale. The reason that such agreement is possible for Celsius and Fahrenheit is the fact that the actual degree units have different sizes (recall the previous question).

ConcepTest 16.3 Thermometers 1) the mercury contracts before the glass contracts 2) the glass contracts before the mercury contracts 3) the mercury contracts before the glass expands 4) the glass expands before the mercury expands 5) the mercury expands before the glass contracts You may notice that if a mercury-in-glass thermometer is inserted into a hot liquid, the mercury column first drops, and then later starts to rise (as you expect). How do you explain this drop?

ConcepTest 16.3 Thermometers 1) the mercury contracts before the glass contracts 2) the glass contracts before the mercury contracts 3) the mercury contracts before the glass expands 4) the glass expands before the mercury expands 5) the mercury expands before the glass contracts You may notice that if a mercury-in-glass thermometer is inserted into a hot liquid, the mercury column first drops, and then later starts to rise (as you expect). How do you explain this drop? The hot liquid touches the glass first, so initially the glass expands slightly. This increases the volume inside the glass, and so the mercury level drops slightly. Once the mercury heats up, it begins to expand and then the characteristic rise in the mercury column follows, indicating the increase in temperature that you expected to measure. Follow-up: Is it possible to have the mercury first rise and later drop?

ConcepTest 16.4 Glasses 1) run hot water over them both 2) put hot water in the inner one 3) run hot water over the outer one 4) run cold water over them both 5) break the glasses Two drinking glasses are stuck, one inside the other. How would you get them unstuck?

ConcepTest 16.4 Glasses 1) run hot water over them both 2) put hot water in the inner one 3) run hot water over the outer one 4) run cold water over them both 5) break the glasses Two drinking glasses are stuck, one inside the other. How would you get them unstuck? Running hot water only over the outer glass will allow the outer one to expand, while the inner glass remains relatively unchanged. This should loosen the outer glass and free it.

ConcepTest 16.5a Steel Expansion I A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected? 1) measured lengths will be too small 2) measured lengths will still be accurate 3) measured lengths will be too big

ConcepTest 16.5a Steel Expansion I A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected? 1) measured lengths will be too small 2) measured lengths will still be accurate 3) measured lengths will be too big The tape measure will expand, so its markings will spread out farther than the correct amount. When it is laid down next to an object of fixed length, you will read too few markings for that given length, so the measured length will be too small.

ConcepTest 16.5b Steel Expansion II Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole? 1) gets larger 2) gets smaller 3) stays the same 4) vanishes

ConcepTest 16.5b Steel Expansion II Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole? 1) gets larger 2) gets smaller 3) stays the same 4) vanishes Imagine drawing a circle on the plate. This circle will expand outward along with the rest of the plate. Now replace the circle with the hole, and you can see that the hole will expand outward as well. Note that the material does NOT “expand inward” to fill the hole!! expansion

ConcepTest 16.6a Steel Ring I A steel ring stands on edge with a rod of some material inside. As this system is heated, for which of the following rod materials will the rod eventually touch the top of the ring? 1) aluminum 2) steel 3) glass 4) aluminum and steel 5) all three    Coefficient of volume expansion b (1/°C ) Glass Hg Quartz Air  Al Steel

ConcepTest 16.6a Steel Ring I A steel ring stands on edge with a rod of some material inside. As this system is heated, for which of the following rod materials will the rod eventually touch the top of the ring? 1) aluminum 2) steel 3) glass 4) aluminum and steel 5) all three    Coefficient of volume expansion b (1/°C ) Glass Hg Quartz Air  Al Steel Aluminum is the only material that has a larger b value than the steel ring, so that means that the aluminum rod will expand more than steel ring. Thus, only in that case does the rod have a chance of reaching the top of the steel ring.

ConcepTest 16.6b Steel Ring II You want to take apart a couple of aluminum parts held together by steel screws, but the screws are stuck. What should you do? 1) heat the thing up 2) cool the thing down 3) blow the thing up    Coefficient of volume expansion b (1/°C ) Glass Hg Quartz Air  Al Steel

ConcepTest 16.6b Steel Ring II You want to take apart a couple of aluminum parts held together by steel screws, but the screws are stuck. What should you do? 1) heat the thing up 2) cool the thing down 3) blow the thing up    Coefficient of volume expansion b (1/°C ) Glass Hg Quartz Air  Al Steel Since aluminum has a larger b value, that means aluminum expands more than steel. Thus, by heating the part, the aluminum holes will expand faster than the steel screws and the screws will come loose.

ConcepTest 16.8a Thermal Contact I Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1) the one with the higher initial temperature 2) the one with the lower initial temperature 3) the one with the greater mass 4) the one with the smaller mass 5) the one with the higher specific heat

ConcepTest 16.8a Thermal Contact I Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1) the one with the higher initial temperature 2) the one with the lower initial temperature 3) the one with the greater mass 4) the one with the smaller mass 5) the one with the higher specific heat Since the objects are made of the same material, the only difference between them is their mass. Clearly, the object with less mass will change temperature more easily since not much material is there (compared to the more massive object).

ConcepTest 16.8b Thermal Contact II Two different objects receive the same amount of heat. Which of the following choices is NOT a reason why the objects may have different temperature changes? 1) they have different initial temperatures 2) they have different masses 3) they have different specific heats

ConcepTest 16.8b Thermal Contact II Two different objects receive the same amount of heat. Which of the following choices is NOT a reason why the objects may have different temperature changes? 1) they have different initial temperatures 2) they have different masses 3) they have different specific heats Since Q = m c DT and the objects received the same amount of heat, the only other factors are the masses and the specific heats. While the initial temperature is certainly relevant for finding the final temperature, it does not have any effect on the temperature change DT.

ConcepTest 16.9 Two Liquids Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat? 1) the cooler one 2) the hotter one 3) both the same

ConcepTest 16.9 Two Liquids Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat? 1) the cooler one 2) the hotter one 3) both the same Both liquids had the same increase in internal energy, because the same heat was added. But the cooler liquid had a lower temperature change. Since Q = mcDT, if Q and m are both the same and DT is smaller, then c (specific heat) must be bigger.

ConcepTest 16.10a Night on the Field The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down? 1) the concrete parking lot 2) the baseball field 3) both cool off equally fast

ConcepTest 16.10a Night on the Field The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down? 1) the concrete parking lot 2) the baseball field 3) both cool off equally fast The baseball field, with the lower specific heat, will change temperature more readily, so it will cool off faster. The high specific heat of concrete allows it to “retain heat” better and so it will not cool off so quickly – it has a higher “thermal inertia.”

ConcepTest 16.10b Night on the Beach Water has a higher specific heat than sand. Therefore, on the beach at night, breezes would blow: (1) from the ocean to the beach (2) from the beach to the ocean (3) either way, makes no difference

ConcepTest 16.10b Night on the Beach Water has a higher specific heat than sand. Therefore, on the beach at night, breezes would blow: (1) from the ocean to the beach (2) from the beach to the ocean (3) either way, makes no difference Daytime sun heats both the beach and the water beach heats up faster warmer air above beach rises cooler air from ocean moves in underneath breeze blows ocean  land csand < cwater Nighttime sun has gone to sleep beach cools down faster warmer air is now above the ocean cooler air from beach moves out to the ocean breeze blows land  ocean

ConcepTest 16.11 Calorimetry (1) 0 oC (2) 20 oC (3) 50 oC (4) 80 oC (5) 100 oC 1 kg of water at 100 oC is poured into a bucket that contains 4 kg of water at 0 oC. Find the equilibrium temperature (neglect the influence of the bucket).

ConcepTest 16.11 Calorimetry (1) 0 oC (2) 20 oC (3) 50 oC (4) 80 oC (5) 100 oC 1 kg of water at 100 oC is poured into a bucket that contains 4 kg of water at 0 oC. Find the equilibrium temperature (neglect the influence of the bucket). Since the cold water mass is greater, it will have a smaller temperature change! The masses of cold/hot have a ratio of 4:1, so the temperature change must have a ratio of 1:4 (cold/hot). Q1 = Q2 m1cDT1 = m2cDT2 DT1 / DT2 = m2 / m1

ConcepTest 17.1a Nitrogen and Oxygen I Which has more molecules – a mole of nitrogen (N2) gas or a mole of oxygen (O2) gas? 1) oxygen 2) nitrogen 3) both the same

ConcepTest 17.1a Nitrogen and Oxygen I Which has more molecules – a mole of nitrogen (N2) gas or a mole of oxygen (O2) gas? 1) oxygen 2) nitrogen 3) both the same A mole is defined as a quantity of gas molecules equal to Avogadro’s number (6.02  1023). This value is independent of the type of gas.

ConcepTest 17.1b Nitrogen and Oxygen II Which weighs more – a mole of nitrogen (N2) gas or a mole of oxygen (O2) gas? 1) oxygen 2) nitrogen 3) both the same

ConcepTest 17.1b Nitrogen and Oxygen II Which weighs more – a mole of nitrogen (N2) gas or a mole of oxygen (O2) gas? 1) oxygen 2) nitrogen 3) both the same The oxygen molecules have a molecular mass of 32, while the nitrogen molecules have a molecular mass of 28. Follow-up: Which one will take up more space?

ConcepTest 17.2a Ideal Gas Law I Two identical cylinders at the same temperature contain the same gas. If A contains three times as much gas as B, which cylinder has the higher pressure? 1) cylinder A 2) cylinder B 3) both the same 4) it depends on temp. T

ConcepTest 17.2a Ideal Gas Law I Two identical cylinders at the same temperature contain the same gas. If A contains three times as much gas as B, which cylinder has the higher pressure? 1) cylinder A 2) cylinder B 3) both the same 4) it depends on temp. T Ideal gas law: PV = nRT Solve for pressure: P = nRT / V For constant V and T, the one with more gas (the larger value of n) has the higher pressure P.

ConcepTest 17.2b Ideal Gas Law II Two identical cylinders at the same pressure contain the same gas. If A contains three times as much gas as B, which cylinder has the higher temperature? 1) cylinder A 2) cylinder B 3) both the same 4) it depends on the pressure P

ConcepTest 17.2b Ideal Gas Law II Two identical cylinders at the same pressure contain the same gas. If A contains three times as much gas as B, which cylinder has the higher temperature? 1) cylinder A 2) cylinder B 3) both the same 4) it depends on the pressure P Ideal gas law: PV = nRT Solve for temperature: T = PV / nR For constant V and P, the one with less gas (the smaller value of n) has the higher temperature T.

ConcepTest 17.2c Ideal Gas Law III Two identical cylinders at the same temperature contain the same gas. If B has twice the volume and half the number of moles as A, how does the pressure in B compare with the pressure in A? 1) PB = 1/2 PA 2) PB = 2 PA 3) PB = 1/4 PA 4) PB = 4 PA 5) PB = PA

ConcepTest 17.2c Ideal Gas Law III Two identical cylinders at the same temperature contain the same gas. If B has twice the volume and half the number of moles as A, how does the pressure in B compare with the pressure in A? 1) PB = 1/2 PA 2) PB = 2 PA 3) PB = 1/4 PA 4) PB = 4 PA 5) PB = PA Ideal gas law: PV = nRT Since B has a factor of twice the volume, it has a factor of two less the pressure. But B also has half the amount of gas, so that is another factor of two reduction in pressure. Thus, B must have only 1/4 the pressure of A.

ConcepTest 17.3 Soda Bottle A plastic soda bottle is empty and sits out in the sun, heating the air inside. Now you put the cap on tightly and put the bottle in the fridge. What happens to the bottle as it cools? 1) it expands and may burst 2) it does not change 3) it contracts and the sides collapse inward 4) it is too dark in the fridge to tell

ConcepTest 17.3 Soda Bottle A plastic soda bottle is empty and sits out in the sun, heating the air inside. Now you put the cap on tightly and put the bottle in the fridge. What happens to the bottle as it cools? 1) it expands and may burst 2) it does not change 3) it contracts and the sides collapse inward 4) it is too dark in the fridge to tell The air inside the bottle is warm, due to heating by the sun. When the bottle is in the fridge, the air cools. As the temperature drops, the pressure in the bottle also drops. Eventually, the pressure inside is sufficiently lower than the pressure outside (atmosphere) to begin to collapse the bottle.

ConcepTest 17.4 Balloon in Freezer 1) it increases 2) it does not change 3) it decreases What happens to the volume of a balloon if you put it in the freezer?

ConcepTest 17.4 Balloon in Freezer 1) it increases 2) it does not change 3) it decreases What happens to the volume of a balloon if you put it in the freezer? According to the Ideal Gas Law, when the temperature is reduced at constant pressure, the volume is reduced as well. The volume of the balloon therefore decreases. nRT PV = Follow-up: What happens to the volume when the balloon rises in the air?

ConcepTest 17.5 Adding Heat If you add some heat to a substance, is it possible for the temperature of the substance to remain unchanged? 1) yes 2) no

ConcepTest 17.5 Adding Heat If you add some heat to a substance, is it possible for the temperature of the substance to remain unchanged? 1) yes 2) no Yes, it is indeed possible for the temperature to stay the same. This is precisely what occurs during a phase change – the added heat goes into changing the state of the substance (from solid to liquid or from liquid to gas) and does not go into changing the temperature! Once the phase change has been accomplished, then the temperature of the substance will rise with more added heat. Follow-up: Does that depend on the substance?

ConcepTest 17.6 Hot Potato Will potatoes cook faster if the water is boiling faster? 1) yes 2) no

ConcepTest 17.6 Hot Potato Will potatoes cook faster if the water is boiling faster? 1) yes 2) no The water boils at 100 °C and remains at that temperature until all of the water has been changed into steam. Only then will the steam increase in temperature. Since the water stays at the same temperature, regardless of how fast it is boiling, the potatoes will not cook any faster. Follow-up: How can you cook the potatoes faster?

ConcepTest 17.7 Water and Ice You put 1 kg of ice at 0oC together with 1 kg of water at 50oC. What is the final temperature? LF = 80 cal/g cwater = 1 cal/g oC 1) 0oC 2) between 0oC and 50oC 3) 50oC 4) greater than 50oC

ConcepTest 17.7 Water and Ice You put 1 kg of ice at 0oC together with 1 kg of water at 50oC. What is the final temperature? LF = 80 cal/g cwater = 1 cal/g oC 1) 0oC 2) between 0oC and 50oC 3) 50oC 4) greater than 50oC How much heat is needed to melt the ice? Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal How much heat can the water deliver by cooling from 50oC to 0oC? Q = cwater m DT = (1 cal/g oC)  (1000g)  (50oC) = 50,000 cal Thus, there is not enough heat available to melt all the ice!! Follow-up: How much more water at 50oC would you need?

ConcepTest 17.8 Ice and Steam You put 1 kg of ice at 0oC together with 1 kg of steam at 100oC. What is the final temperature? LF = 80 cal/g, Lv = 540 cal/g cwater = 1 cal/g oC 1) between 0oC and 50oC 2) 50oC 3) between 50oC and 100oC 4) 100oC 5) greater than 100oC

ConcepTest 17.8 Ice and Steam You put 1 kg of ice at 0oC together with 1 kg of steam at 100oC. What is the final temperature? LF = 80 cal/g, Lv = 540 cal/g cwater = 1 cal/g oC 1) between 0oC and 50oC 2) 50oC 3) between 50oC and 100oC 4) 100oC 5) greater than 100oC How much heat is needed to melt the ice? Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal How much heat is needed to raise the water temperature to 100oC? Q = cwater m DT = (1 cal/g oC)(1000g)(100oC) = 100,000 cal But if all of the steam turns into water, that would release 540,000 cal. Thus, some steam is left over, and the whole mixture stays at 100oC. Follow-up: How much more ice would you need?

ConcepTest 17.9 You’re in Hot Water! 2) steam 3) both the same 4) it depends... Which will cause more severe burns to your skin: 100 °C water or 100 °C steam?

ConcepTest 17.9 You’re in Hot Water! 2) steam 3) both the same 4) it depends... Which will cause more severe burns to your skin: 100 °C water or 100 °C steam? While the water is indeed hot, it releases only 1 cal/g of heat as it cools. The steam, however, first has to undergo a phase change into water and that process releases 540 cal/g, which is a very large amount of heat. That immense release of heat is what makes steam burns so dangerous.

ConcepTest 17.10 Spring Break You step out of a swimming pool on a hot day, where the air temperature is 90° F. Where will you feel cooler, in Phoenix (dry) or in Philadelphia (humid)? 1) equally cool in both places 2) Philadelphia 3) Phoenix

ConcepTest 17.10 Spring Break You step out of a swimming pool on a hot day, where the air temperature is 90° F. Where will you feel cooler, in Phoenix (dry) or in Philadelphia (humid)? 1) equally cool in both places 2) Philadelphia 3) Phoenix In Phoenix, where the air is dry, more of the water will evaporate from your skin. This is a phase change, where the water must absorb the heat of vaporization, which it takes from your skin. That is why you feel cool as the water evaporates.

ConcepTest 18.1 Free Expansion A free expansion occurs when a valve is opened allowing a gas to expand into a bigger container. In such an expansion the temperature of the gas will: 1) increase 2) decrease 3) stay the same

ConcepTest 18.1 Free Expansion A free expansion occurs when a valve is opened allowing a gas to expand into a bigger container. In such an expansion the temperature of the gas will: 1) increase 2) decrease 3) stay the same In such a process: W = 0 there is no object to move, Q = 0 there is no heat exchange, therefore U = 0 by the First Law of Thermodynamics. Thus, there is no change in the temperature. Free expansion is an irreversible process --- the gas molecules have virtually no chance of returning to the original state. Free expansion is neither adiabatic nor isothermal expansion, even though T and Q are zero.

ConcepTest 18.2 Work P V 1) positive 2) zero 3) negative In the closed thermodynamic cycle shown in the P-V diagram, the work done by the gas is: 1) positive 2) zero 3) negative V P

ConcepTest 18.2 Work P V 1) positive 2) zero 3) negative In the closed thermodynamic cycle shown in the P-V diagram, the work done by the gas is: 1) positive 2) zero 3) negative The gas expands at a higher pressure and compresses at a lower pressure. In general, clockwise = positive work; counter-clockwise = negative work. V P

ConcepTest 18.3 Heat Engine The heat engine below is: 1) a reversible (Carnot) heat engine 2) an irreversible heat engine 3) a hoax 4) none of the above

ConcepTest 18.3 Heat Engine The heat engine below is: 1) a reversible (Carnot) heat engine 2) an irreversible heat engine 3) a hoax 4) none of the above Carnot e = 1-TC/TH=1-270/600=0.55. But by definition e = 1-QL/QH =1 - 4000/8000=0.5, smaller than Carnot e, thus irreversible. Follow-up: What would you need to change to make it a Carnot engine?