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exam1Soln2

# exam1Soln2 - 1 A brass rod is 69.5 cm long and an aluminum...

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1. A brass rod is 69.5 cm long and an aluminum rod is 49.0 cm long when both rods are at an initial temperature of 0 o C. The rods are placed in line with a gap of 1.5 cm between them. The distance between the far ends of the rods is maintained at 120.0 cm throughout. The temperature is raised until the two rods are barely in contact. The coefficients of linear expansion of brass and aluminum are 2.0 x 10 -5 K -1 and 2.4 x 10 -5 K -1 , respectively. The temperature at which the rods just touch each other , in o C, is closest to: a. 643 b. 555 c. 526 d. 614 *e. 585 General Feedback: 1 2 1 1 2 2 1 1 2 2 1 1 2 2 ( 0)( ) 585 ( ) o x x x L T L T T L L x T C L L α α α α α α = ∆ + ∆ = + = + = = + 2. A substance has a melting point of 20 o C and a heat of fusion of 1.9 x 10 4 J/kg. The boiling point is 150 o C and the heat of vaporization is 3.8 x 10 4 J/kg at a pressure of one atmosphere. The specific heats for the solid, liquid, and gaseous phases are 600, 1000, and 400 J/kgK, respectively. The quantity of heat required to raise the temperature of 1.00 kg of the substance from -5 o C to 129 o C, in kJ, is closest to: General Feedback: Substance warms, melts, warms but does not boil 143 s s L L Q mc T mL mc T kJ = + + =

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3. A 220 g metal container, insulated on the outside, holds 110 g of water in thermal equilibrium at 22 o C. A 24 g ice cube, at the melting point, is dropped into the water, and when thermal equilibrium is reached the temperature is 15 o C. Assume there is no heat exchange with the surroundings. For water, the specific heat capacity is 4190 J/kg K and the heat of fusion is 3.34 x 10 5 J/kg. The specific heat capacity for the metal is closest to: *a. 4090 J/kg K b. 3110 J/kg K c. 4690 J/kg K d. 5190 J/kg K e. 6185 J/kg K General Feedback: | | | | | | 15 7 7 15 7 7 4090 / ice metal w i i w m m w w i i w w w m m m Q Q Q m L m c m c m c m L m c m c c m c J kgK = + + = + + = = 4. In the figure below, heat is added to a pure substance in a closed container at a constant rate. A graph of the temperature of the substance as a function of time is shown here. If LF = latent heat of fusion and LV = latent heat of vaporization, what is the value of the ratio LV/LF for this substance? *d. 3.5 General Feedback:
Since time is 7/2 longer to boil the substance than melt it, LV/LF = 7/2 5. You have two containers of equal volume. One is full of helium gas. The other holds an equal mass of nitrogen gas. Both gases have the same pressure. How does the temperature of the helium compare to the termpature of the nitrogen? *c. helium nitrogen T T < General Feedback: PV same for both conatiners. The mass is also the same, but since the molar mass for He is less than the molar mass for nitrogen, there must be more moles in the He container. Via the ideal gas law, since PV is the same, nRT is the same for both containers, hence THe < TN

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