W4.W (completed) - Specific heat, transformations, calorimetry Tuesday, January 27, 2015 4:35 PM Warm up: How much energy must be removed from a 200 g block of ice to cool it from 0°C to -30°C? (specific heat of ice is 2090 J/(kg K) 1. 2. 3. 4. 5. 10,500 J 11,500 J 12,500 J 13,500 J 14,500 J New Section 1 Page 1 100 g of each of the following materials is heated. Each material gets the same amount of heat. Which material will increase in temperature the most? Copper: density=8.96 g/cc, melting point 1085°C, c = 385 J/kg°C, conductivity = 401 W/m°C Magnesium: density= 1.74 g/cc, melting point = 650°C, c = 1020 J/kg°C, conductivity = 156 W/m°C Aluminum: density= 2.70 g/cc, melting point = 660°C, c = 897 J/kg°C, conductivity = 237 W/m°C An ice cube at a temperature of −20ºC is put in a plastic bowl and placed in a microwave oven, and the oven is turned on. When the oven is turned off, the bowl contains water at a temperature of +60ºC. Assuming the microwave transferred energy to the ice at a constant rate throughout, draw a graph of the temperature of the H2O as a function of time. The endpoints of the graph are given. New Section 1 Page 2 The graph shows the temperature as a function of energy supplied to 1 kg of H 2O. If 200 kJ of energy is added, will the temperature rise more during the solid or liquid phase? If the H2O is initially at -100ºC, and put in a microwave that deposits a constant rate of energy, which will take longer amount of time? (a) reaching the liquid state (b) going from the liquid to the gas state (c) both will take the same amount of time Samples of two pure substances are heated at a constant rate, and their temperature as a function of time is recorded. Both substances started as solids and melted. The mass of the two samples is the same. The latent heat of fusion of substance A is ______ the latent heat of fusion of substance B. 1. greater than New Section 1 Page 3 the same. The latent heat of fusion of substance A is ______ the latent heat of fusion of substance B. 1. greater than 2. less than 3. equal to Rank the solid and liquid specific heats of the two substances in one ranking The melting point of substance A is _______ the melting point of substance B? 1. greater than 2. less than 3. equal to How much energy must be removed from a 200 g of water to cool it from 0°C to -30°C? (specific heat of ice is 2090 J/(kg K), Lf = 3.33 x 105 J/kg, Lv = 22.6 x 105 J/kg) 1. 2. 3. 4. 5. 32,500 J 12,500 J 65,310 J 81,554 J 79,100 J A 2.00-kg metal block slides on a rough, horizontal surface inside an insulated box. After sliding a distance of 500.0 m, its temperature is increased by 2.00 ºC. Note: assume that all of the heat generated by the frictional work goes into the metal block. For this metal, the specific heat capacity is 0.150 cal/(g·Cº). (a) How much energy goes into block by the friction force? (b) What is the coefficient of kinetic friction between the block and the surface? New Section 1 Page 4 30 g of copper pellets are removed from a 300ºC oven and immediately dropped into 100 mL of water at 20ºC in an insulated cup. What will the equilibrium temperature of the water be? The specific heat of copper and water are 385 J/(kg·K) and 4190 J/(kg·K) respectively. 1 liter is equal to 1000 cm3. New Section 1 Page 5 Objects A and B are brought into close thermal contact with each other, but they are well isolated from their surroundings. Initially T A = 0°C and TB = 100°C. The specific heat of A is more than the specific heat of B. The two objects will soon reach a common final temperature T f. The final temperature is 1. Tf > 50°C 2. Tf < 50°C 3. Tf = 50°C In an experiment, 50 g of steam at 100ºC and 50 g of water at 80ºC are mixed together in an insulated container, and are allowed to reach thermal equilibrium. When the combination reaches thermal equilibrium, the mass of water (liquid) be _____ the sum (100 g) of the two initial masses. New Section 1 Page 6 thermal equilibrium, the mass of water (liquid) be _____ the sum (100 g) of the two initial masses. 1. greater than 2. less than 3. the same as New Section 1 Page 7