Purpose The purpose of this lab is to introduce the student to the concepts of heat transfer, specic heat capacity and phase change. Introduction As you learned in the Energy lab, energy can be transferred from one object to another, or transformed from one form of energy to another. Energy can be transferred to or from a system in one of two ways: work can be done on or by a system and heat can be added to or removed from the systemr Remember Work (W) is a transfer of mechanical energy by a force acting on a system through a distance Work can change the mechanical and or thermal energy of a system. (remember mechanical energy includes kinetic energy and potential energy). Heat (Q) is a transfer of energy between two objects with different temperatures, changing the thermal energy of a system. Both work and heat have SI units of Joules (J). Heat is also sometimes measured in units of calories (gal). A calorie is the amount of heat needed to raise the temperature of 1 gram of water 1 degree Celsius. Thermal energy (Em) is a macroscopic measurement of the total amount of kinetic and potential energy of all the microscopic molecules that make up an object. The thermal energy of a substance depends on its mass, its temperature and the specic material of which it is made, Temperature (T), measured in SI units of kelvin (K) or in degrees Celsius CC), is a macroscopic quantication of the average kinetic energy of the individual molecules that make up an object, As the temperature of an object increases, the average speed of the particles that make up the object increases. For a solid object, the molecules of the object Vibrate faster as the temperature and thermal energy increase. An increase in thermal energy can lead to a phase change from solid to liquid or liquid to gas when molecular bonds break, The difference between heat and temperature is that heat describes the amount of energy needed to warm an area or object, while temperature is a numerical reading of how warm that area or object is. Heat is produced by the constant movement of molecules. When heat is added to an object, the movement of the object's molecules is increased, The speed with which these molecules move determines the temperature of the body, The greater the speed of movement of the molecules, the higher the temperature Specific Heat Capacity Heat normally ows from a warmer to a colder body, One object gives off heat while another absorbs heat, The quantity of heat which must ow into or out of a unit mass of a substance to change its temperature by one degree is called the specic heat cagacig sometimes called the specic heat) of the substance, measured in units of J/lvggvlvg or gal/gmc. The specific heat capacity of an object depends only on the substance from which the object is made The specic heat capacity for water is L00 gal/gf or 4190 1% meaning that one calorie of energy is required to raise the temperature of one gram of water by one degree Celsius, and 4190 joules of energy are required to raise the temperature of one kilogram of water by one kelvinr Specific Heat Capacity is like thermal inertia Remember inertia is a measure of an object's resistance to change its motion Specific Heat Capacity is a measure of an object's resistance to change its temperature. The specic heat capacities of some common substances are listed in Table 1 below. Table 1 Specific Heat capacities of come common substances Material Specific Heat Capacities cal/g. C Lead ).03 Steel 0.107 Glass 0.15 Aluminum 0.21 Air 0.239 Styrofoam 0.2701 Ice 0.50 Alcohol 0.55 Human Body 0.83 Water 1.00 Note that water has a very high specific heat capacity in comparison to most other materials. This implies that a given mass of water will be more resistant to changing its temperature than an equal mass of material with lower specific heat capacity. Substances with high specific heats require more heat transfer to change their temperatures than substances with low specific heats. A high specific heat substance takes longer to warm up or cool down than a low specific heat substance. For two substances of equal mass and temperature, the higher specific heat substance has more heat energy. Calorimetry Calorimetry is the measurement of the heat transfer between systems. Calorimetry can measure the specific heat of a substance using a calorimeter. A calorimeter creates a system isolated from the surrounding environment, facilitates heat transfer between the objects within the system, and allows for the measurement of the temperature of the system before and after a reaction or interaction. The heat required to change the temperature of a substance is given by the equation: Q = mcAT Where, Q = heat (cal) M = mass (8) c = specific heat (Cal/g.C) AT = Change in temperature The change in temperature, AT, is always equal to the final temperature minus the initial temperature: AT = Tf - Ti Where, If = final temperature Ti = initial temperature This means that for a substance becoming colder during an interaction, the change in temperature is negative, and therefore the heat required to cause that temperature change is also negative. The final temperature of two objects in thermal contact is the equilibrium temperature and is the same for both objects.In a closed system, such as in a calorimeter, net heat = 0 (the heat transferred out of the hot object is equal to the heat transferred into the cold object). For a system with two substances, the energy conservation equation can be combined with the heat equation: mic1AT1 + m2czAT2 = 0 The above equation can then be rearranged to solve for the specific heat of one of the substances, as long as the specific heat of the other substance is known. In the basic calorimeter used in this experiment, the first substance is always water, which has a specific heat of 1.00 cal/g. C. If the specific heat of both substances is known, one of the other variables, such as the initial temperature of one of the substances, can be solved for instead. For this lab you will be placing hot metal objects into room temperature water in a calorimeter. For this set up: Qout of metal + into water = 0 mwaterwaterATwater + mmetal metalATmetal = 0 mwaterCwater(Tf - Tiw) + mmetal Cmetal (Tf - Tim) = 0 Where: mwater = mass of the water mmetal=mass of the metal Cwater = specific heat of water (1.00 cal/& C) Cmetal = specific heat of the metal If = final equilibrium temperature of the system (same for both the metal and the water) Tiw = initial temperature of the water Tim = initial temperature of the metal Using the above equation, you can rearrange and solve for the specific heat capacity of the metal (highlighted in green in the equation below). mwaterCwater(Tf - Tiw) + mmetal metal (Tf - Tim) = 0 mmetal metal (Tf - Tim) = - mwaterCwater(Tf - Tiw) Divide both sides by the mass of the metal: Cmetal (Tf - Tim) = - mwaterCwater (Tf - Tiw) mmetal Divide both sides by the change in temperature of the metal: - mwater Cwater (Tf - Tiw) Cmetal = mmetal (Tf - Tim)Note: the negative sign in the above equation is a result of the fact that the change in temperature of the metal itself will be negative The final temperature of the metal is less than the initial temperature of the metal, so the change in temperature is negative The overall result will be a positive value for the specic heat capacity of the metal Ii'llth calorimeter is rarely a perfectly isolated system, which can lead to slight discrepancies between the theoretical predictions and the actual experimental results of a process, Some heat energy may transferred to the calorimeter itself or become lost to the environment, The Step by Step procedures for this lab are on the remaining pages below. Gather the following materials Student Supplied HOL Supplied Cooking pot for boiling water Brass ball 2 Drinkingglasses Digital scale, precision Metal Fork Safetxggggles Pair of scissors Ruler Pen or pencil 3 Styrofoam cups Source of tap water Thermometer Stove top or hot plate 5 Washers NOTE: At least one hour before starting this exercise, ll a large drinking glass and a small glass with tap water and let is sit so it can reach room temperature The large glass will provide room temperature water for 4 trials in the experiment, the small glass will be used to cool the thermometer between measurements Procedure I Data collection Determining the Specic Heat Capacity of Solids Part 1: Constructing a Calorimeter Note: To minimize heat exchange with the environment, you will use a wellinsulated calorimeter for this experiment. Three Styrofoam cups will build the calorimeter 7 two (one inside the other) to form the base and one as a cover. 1. Create a calorimeter as shown in Figure 1 below. Place two Styrofoam cups together such that one sits inside the other, 2. Use scissors to trim the third Styrofoam cup to a height of approximately 5 cm, 3. Create a small hole in the bottom of the 5 cm cup using a pen or pencil. Note: the hole should be small enough such that the thermometer will t tightly in the hole. This will limit the amount of heat escaping the calorimeter and prevent the thermometer from shifting position signicantly. thermometer doubled cup thermometer bole doubled um base Figure l Calorimeter using 3 Styrofoam Cups Part 2: Data collection Turn on the digital scale and select the gram function. Place ve washers on the digital scale and record the mass to 0.01 g in Data Table 1 Remove the washers from the digital scale. Place a small piece of crumpled paper on the digital scale. Tare the scale. Place the brass ball on the crumpled paper on the scale and record the mass to 001 g in Data Table 1, Using scissors, cut a 30 cm string and securely tie the ve metal washers together (you can use the same strings you used for the torque lab and tie using a slip knot.) Place the washers and the brass ball in a cooking pot and ll with tap water to approximately 10 cm above both objects. Place the pot on a cooktop and heat the water to boiling, PSV 5.0 Note: Avoid using a microwave for heating the water. Only use a cooktop or heat plate. 12. Place the doubled cup on the digital scale and press the power button once to tare the scale. 13. Pour 75 80 g of the room temperature water ti'om the large glass into the double cup. Record the mass to 0.01 g in Data Table 1, 14. Remove the double cup containing the water from the scale. 15. Insert the thermometer into the calorimeter base such that its tip is in the water. Record the temperature of the water to 01C in Data Table 1. NOTE: Avoid touching the thermometer to the sides of the calorimeter when measuring the temperature of the water. You will need to ensure the thermometer has reached the temperature of the water, so you might need to keep the thermometer in the water for about 10-15 seconds before reading the water temperature. 16. Be sure the water is rlly boiling before continuing. Once the water in the pot is boiling, reduce the heat to maintain a gentle boil for 10 minutes, stirring occasionally. 17. Use the thermometer to measure the temperature of the boiling water near the washers to 01C The boiling water and the washers are in thermal equilibrium, so the temperature of the water is the same as the temperature of the washers, Note: Avoid touching the thermometer to the sides or bottom of the pot. Avoid holding your hand directly over the steaming water hold the thermometer to the side. 18. Remove the thermometer from the hot water and place it in the small glass of water. Allow it to cool for 10-15 seconds then place the thermometer into the calorimeter lid. 19. Leave the boiling water on the heat m ensure there is enough water remaining to complete three more trials. 20. It is important that you complete this step quickly so carefully read and understand the entire step before completing it. Hold the calorimeter close to the pot of water with the lid off Using a metal fork, quickly transfer the washers from the boiling water to the calorimeter containing the room temperature water. Quickly cover the calorimeter with the foam lid and push it down gently so the calorimeter is sealed. Note: Avoid adding boiling water to the calorimeter. For best results, leave the string attached to the washers hanging outside the doubled cup. 21. Carefully insert the thermometer through the hole in the calorimeter lid, positioning the tip in the water near the washers without touching them. 22. Gently stir the water in the cup with the thermometer, Note: Avoid removing the calorimeter lid. Do not allow the thermometer to touch the sides or bottom of the cup or the washers. 23. Observe the thermometer as the temperature stabilizes, checking the temperature every 10-15 seconds. Record the maximum water temperature reached to 0.1\"C as the nal temperature of the water and washers in Data Table 1, Note: You may need to slide the thermometer up slightly to see the reading. If so, do this periodically (every 10-15 seconds) and always return the thermometer into the water immediately afterward. Avoid removing the thermometer completely from the calorimeter or lifting the lid of the calorimeter when taking measurements. 24. Return the washers to the boiling water and discard the water in the calorimeter, 25. Repeat steps 12-24 above for the brass ball instead of the washers recording the data as Trial 2, 26. Wait another 10 minutes with the washers and the brass ball in the boiling water, then repeat Steps 1224 again for both the washers and the brass ball to obtain a second set of data for each and record in data table 1 as Trial 3 & 4. 27. Turn off the heat and remove the pan, Procedure 11 Data Analysis 28. Calculate the change in temperature of the water and washers for Trials 1 & 3 and the change in temperature of the water and the brass ball for trials 2 & 4 using the equation: AT = T, T,- 29. Record the change in temperature for the four Trials to 01C in Data Table 1. 30. Calculate the specic heat capacity of the washers using the equation derived above based upon the equation for specic heat and the equation for conservation of energy: mwatercwuter (Tf Tiw) mmetal(T/' _ Tim) [metal : Where: mwum ' mass of the water mmm mass of the metal 6mm, specic heat of water (1 .00 gal/gDC) cmem; = specic heat of the metal 13; nal equilibrium temperature of the system (same for both the metal and the water) Tiw = i itial temperature of the water Tim = initial temperature of the metal 31. Record the specic heat capacity in Data Table 2 32. Repeat step 30-31 above for three remaining trials. 33. Calculate the average specic heat capacity from Trials 1 & 3 for the washers and record in Data table 2, 34. Calculate the average specic heat capacity from Trials 2 & 4 for the brass ball and record in Data table 2, 35. Calculate the percent error between the calculated value and the theoretical error for the washers using the equation: Icmetalmheary _ Cmemmvemge Percent Error = x 100% cmetalmheory Note: the values for cmmltheow are locatedin Data Table 2, 36. Record the percent error for the washers in Data Table 2. 37. Repeat steps 33-34 for the brass ball. 38. Were your experimental results within 10% of the theoretical values? If not explain what experimental factors contributed to this error, Cleanup: Procedure I Data Collection Data Table 1 Initial Final Change in Material Mass (g) Temprature Temperature Temperature Water 78.5 20c Trial 1 26c Steel Washers 28.57 100c Water 75.9 20c Trial 2 28c Brass Ball 70 101c Water 78.9 20c Trial 3 27c Steel Washers 28.57 102c Water 76.6 20c Trial 4 Brass Ball 70 30c 100c Data Analysis Table 2 Specific Heat Specific Heat Average Material Exp 1 Exp 2 Specific Heat Steel Washers Brass Ball Steel Washers Brass Ball Average Specific Heat Material Specific Heat theory Percent Error Within 10% Steel Washers 0.122 Brass Ball 0.091 What experimental factors might contribute to your data collection errors