# Consider the experiment described in Example 20.2. You realize that your calorimeter is not perfect, that is, although you would like the system to be.

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Consider the experiment described in Example 20.2. You realize that your calorimeter is not perfect, that is, although you would like the system to be isolated, heat can transfer between the calorimeter and the room. To obtain the best results for your experiment, you should use water with an initial temperature that is a) slightly less than the temperature of the room, b) exactly the same as the temperature of the room, c) slightly greater than the temperature of the room, or d) any starting temperature will yield the same results. (end of section 20.2) QUICK QUIZ 20.1

(a). Recall from the experiment that the final equilibrium temperature of the ingot-water mixture is higher than the initial temperature of the water. Since some heat can enter or leave the system from the room, you would like the heat entering the system at the start of the experiment, when the water is cold, to be compensated by the heat leaving the system at the end of the experiment, when the water is warm. To do this, you should start with water that is at a temperature slightly below room temperature and finish with water (and ingot) at a temperature that is slightly above room temperature. QUICK QUIZ 20.1 ANSWER

After reading the section of this book on latent heat, you come up with an interesting idea for a sleeping bag. You would like to use the latent heat of freezing water to warm you as you sleep. Your idea is to patent a sleeping bag with an outer water compartment that surrounds the entire sleeping bag. If you use this sleeping bag, it will a) work as you predict, warming you as the water starts to freeze, b) work as you predict, but only warming you once all the water is completely frozen, c) work only as the water cools down to 0°C, but not as the water starts to freeze, or d) not work since heat will be transferred from you to the water rather than the other way around. (end of section 20.3) QUICK QUIZ 20.2

(c). Heat is transferred from a body at a higher temperature to a body at a lower temperature. As the water freezes, heat is transferred from the water (at 0°C) to the surrounding air, at a temperature less than 0°C. In addition, since your body temperature is higher than 0°C, heat will transfer from you into the water. Also, water has a higher thermal conductivity than air so the heat will be transferred from you to the water much more quickly. A better solution would be to set a number of barrels of water around the campsite so that heat is transferred to the air and the air is in contact with you. QUICK QUIZ 20.2 ANSWER

Physical properties for three metals are combined in the table below. From these data, there appears to be a correlation between the specific heat and a) the bulk modulus, b) the density, c) the thermal conductivity, or d) none of the above. MaterialBulk Modulus (N/m 2 ) Density (g/cm 3 ) Thermal Conductivity W/(m°C) Specific heat J/(kg°C) Copper 14 x 10 10 8.92397387 Aluminum 7 x 10 10 2.70238900 Iron (or Steel) 6 x 10 10 7.8679.5448 (end of section 20.3) QUICK QUIZ 20.3

(b). The specific heat is greatest for aluminum, then iron and then copper. The only other physical quantity that varies such that aluminum and copper represent the two extremes is density. The density is greatest for copper, then iron, and then aluminum. This is not an isolated fact for these three metals. In general, the specific heat for elemental metals increases as the density decreases. In essence, there are more atoms per kilogram, in a light metal like aluminum, to absorb the energy. If one measures the specific heat in units that relate to the heat transferred per atom, for example J/(mole°C), the values obtained for the different metals are very similar. For aluminum, iron and copper, one obtains, QUICK QUIZ 20.3 ANSWER

The energy transferred by work between a system and its surroundings depends on the path of the process and, in addition, the energy transferred by heat between a system and its surroundings depends on the path of the process. The first law of thermodynamics combines these two quantities in the equation, E int = Q + W. One can say that a) the change in internal energy of a system always depends on the path of the process, b) the change in internal energy of a system sometimes depends on the path of the process, or c) the change in internal energy of a system never depends on the path of the process. (end of section 20.5) QUICK QUIZ 20.4

(c). The first law would seem to imply that the internal energy must be dependent on the path of the process since it is the sum of two quantities that are each dependent on the path of the process. However, the internal energy is a path independent quantity and therefore only depends on the state of the system. It is a very interesting consequence of the first law that such a path independent quantity can exist that is the sum of two path dependent quantities. QUICK QUIZ 20.4 ANSWER

A fire poker is used to push charcoal or logs around in a fireplace. From the issue of safety, you would like the fire poker to be made from a material a) that has a high specific heat and a high thermal conductivity, b) that has a low specific heat and a low thermal conductivity, c) that has a low specific heat and a high thermal conductivity, or d) that has a high specific heat and a low thermal conductivity. (end of section 20.7) QUICK QUIZ 20.5

(d). You would like the specific heat of the poker to be high so that it can absorb a lot of heat with only a small increase in temperature. In addition, you would like the thermal conductivity to be low so that very little heat is conducted from the fire to your hand. QUICK QUIZ 20.5 ANSWER

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