Presentation on theme: "Heat and the First Law of Thermodynamics"— Presentation transcript:
1Heat and the First Law of Thermodynamics Chapter 20Heat and the First Law of Thermodynamics
2Quick Quiz 20.1Imagine you have 1 kg each of iron, glass, and water, and that all three samples are at 10°C. Rank the samples from lowest to highest temperature after 100 J of energy is added to each sample.(a) iron, glass, water(b) iron, water, glass(c) glass, iron, water(d) glass, water, iron(e) water, glass, iron(f) water, iron, glass
3Quick Quiz 20.1Answer: (e). Because water has the highest specific heat (4 186 J/kg · °C), it has the smallest change in temperature. Glass is next (837 J/kg · °C), and iron is last (448 J/kg · °C).
4Quick Quiz 20.2Imagine you have 1 kg each of iron, glass, and water, and that all three samples are at 10°C. Rank them from least to greatest amount of energy transferred by heat if each sample increases in temperature by 20°C.(a) iron, glass, water(b) iron, water, glass(c) glass, iron, water(d) glass, water, iron(e) water, glass, iron(f) water, iron, glass
5Quick Quiz 20.2Answer: (a). Iron, glass, water. For a given temperature increase, the energy transfer by heat is proportional to the specific heat.
6Quick Quiz 20.3Suppose energy is added to an ice cube until it eventually vaporizes into steam, and we graph the internal energy of the system as a function of energy input. What would this graph look like?
7Quick Quiz 20.3Answer: The figure below shows a graphical representation of the internal energy of the ice in parts A to E as a function of energy added. Notice that this graph looks quite different from Figure 20.2 – it doesn’t have the flat portions during the phase changes. Regardless of how the temperature is varying in Figure 20.2, the internal energy of the system simply increases linearly with energy input.
8Quick Quiz 20.4Calculate the slopes for the A, C, and E portions of the figure below. Rank the slopes from least to greatest.(a) A, C, E(b) A, E, C(c) C, E, A(d) C, A, E(e) E, A, C(f) E, C, A
9Quick Quiz 20.4Answer: (d). C, A, E. The slope is the ratio of the temperature change to the amount of energy input. Thus, the slope is proportional to the reciprocal of the specific heat. Water, which has the highest specific heat, has the smallest slope.
10Quick Quiz 20.5In the last three columns of the following table, fill in the boxes with -, +, or 0. For each situation, the system to be considered is identified.SituationSystemQWΔ Eint(a) Rapidly pumping up a bicycle tireAir in the pump(b) Pan of room-temperature water sitting on a hot stoveWater in the pan(c) Air quickly leaking out of a balloonAir originally in the balloon
11Quick Quiz 20.5 Answer: Situation System Q W + - Δ Eint (a) Rapidly pumping up a bicycle tireAir in the pump+(b) Pan of room-temperature water sitting on a hot stoveWater in the pan(c) Air quickly leaking out of a balloonAir originally in the balloon-
12Quick Quiz 20.6a Characterize path A in the figure below: (a) isobaric (b) isovolumetric(c) isothermal(d) adiabatic
20Quick Quiz 20.7An ice cube wrapped in a wool blanket will remain frozen for a _____ length of time than an identical ice cube exposed to air at room temperature.(a) shorter(b) same(c) longer
21Quick Quiz 20.7Answer: (c). The blanket acts as a thermal insulator, slowing the transfer of energy by heat from the air into the cube.
22Quick Quiz 20.8You have two rods of the same length and diameter but they are formed from different materials. The rods will be used to connect two regions of different temperature such that energy will transfer through the rods by heat. They can be connected in series, as in part (a) of the figure below, or in parallel, as in part (b). In which case is the rate of energy transfer by heat larger?(a) when the rods are in series(b) when the rods are in parallel(c) The rate is the same in both cases.
23Quick Quiz 20.8Answer: (b). In parallel, the rods present a larger area through which energy can transfer and a smaller length.