1 Of 3 Heat and Temperature Purpose 1. To study heat, Qhand its relation to temperature, T, mass, m and specific heat, c of the object being heated. 2. To measure the specific heat, c of an object. Introduction Heat is a form of energy transfer. It is associated with the transfer of energy from a hot object to a colder one. Internal energy of an object is the kinetic and potential energy of the molecules of the object. When heat is gained by an object, the heat energy gained goes into increasing the internal energy of the object. There are three common states of matter: Solid, liquid and gas. If an object is not a point of change of state, the heat energy gained goes into increasing the kinetic energy of the molecules of the object. For a solid, the kinetic energy of the molecules is a vibration kinetic energy, where the molecules vibrate about a fixed position. Temperature is a measure of the average kinetic energy of the molecules of an object. Therefore, as heat energy, thlows into an object, the kinetic energy of the molecules increases and the temperature of the object increases. AT increases: Qna AT (1) In the next experiment {Calorimetry and Latent heat) we will discuss the case where the state of the object changes. If the state of the object changes then the heat flowing into the object goes into increasing the potential energy of the molecules not the kinetic energy of the molecules. It is reasonable to think that if an object has a greater mass, m, then the amount of heat, 0}; needed to raise its temperature by a given AT , should be greater: Qh a m (2) Finally, not all types of materials are the same so there must be a factor that depends on the type of material. This factor is called the specific heat {or specific heat capacity), 'c'. c is a constant for a given material. The specific heat, c is defined as the amount of energy needed to raise the temperature of 1 kg of the object by 1 degree. Using eqns. {1) and {2}, the complete formula for thhen is: Qh=chT (3) Since heat is a form of energy being transferred, the unit for the quantity of heat, (2,, is the jouleJ. Another unit is the Calorie, Cal, where 1 Cal = 4-186] and 1 Co! = 1000 ml. {notice the lower case letter). Another scale for the temperature is the Kelvin scale, where T (K) = 273.15 + T (\"(2). But AT (K) = AT (\"(2). Water has a relatively large specific heat, c. This causes the change of temperature of water upon heating {or cooling} of water to require a large quantity of heat, th0 be gained {or lost). 50, heating (or cooling} water requires long time. This fact accounts for the moderate weather {temperature variations) for regions near large bodies of water, {since water is relatively slow to heat {or cool)]. Running the experiment (The data sheet is on page 3) Part 1: Dependence ofchange in temperature, AT on quantity of heat input. 0,,, for a given material and a given mass ofobject, m ll Open the simulator: htt s: iwant25tud .or lookan e'ss 03therma| h sics 09transferofthermalener e'ss model HeatTransfeer HeatTr ansfeer Simulation.xhtml 2} Keep all default settings: Max temp of water in beaker = 100 0C, Heat level: Low. Note the temperature of the water in the beaker at 0.00 minutes is 25 0C. So, T,J = 25 \"C. Do not click the play icon, we will use the Next icon, Next I" which advances the time in steps. 3} If you click the one step advance icon, "Next\" Next Ip once the time will advance by 0.5 minute. Click the advance button Next I. two times to reach a time of 1 minute. Record the temperature as given by the simulator. Increase the time in steps of] minute up to 11 minutes. Each time record the corresponding temperature of the water in the beaker {displayed in the yellow text box}. Record your values in the data sheet in table 1. 4} Plot a graph of time versus change in temperature, AT. Draw the best fit straight line. Notice that we assume the time {we will give it the symbol '65} is proportional to the quantity of heat, 0,, given to the water. So your graph represents the quantity of heat versus temperature. According to equation {3}, the slope {for the actual thersus AT) should be mc: mass of water times the specific heat of water (but we are not using the actual thut only time (it that is proportional to Oh). If the graph is a straight line, then this verifies equation {1}: that the quantity of heat is proportional to the change in temperature for the given mass and a given type of material (here water). Part2: Dependence ofchange in temperature, AT on mass ofobject, m for a given material and a given inputon,I 1} Open the simulator: https:([wwwcompadre.orgPhysletsZthermodynamicszillustration19 1.cfm Wait till it fully loads. Read the explanatory text. 2) Change the mass of blue block to 1 kg, as follows: type 1 in the 'mass =' eld, then click once on _ then click once on ''" \"9"\": '9'" ""\""' . Now the mass of the blue block is set to 1 kg. 3} Click play. Wait till the animation ends [time reaches 5. Notice that the unit for time in the animation is minutes}. Since the power of heating {P = Qh/t) is xed then in a fixed time of 5 minutes, a fixed quantity of heat is delivered to the blue block. Record the final temperature as displayed on the thermometer scale in the table in the data sheet. Click the icon reset: - 4} Repeat steps 2 and 3 for mass of block, In set to 2, 3, 4, 5 kg. Record the values in table 2 in the data sheet. 5} Plot a graph of the change in temperature, AT versus the reciprocal of the mass, (l/m). Draw the best fit straight line. This shows that for a given material, the more the mass of the material, m, the less the change in temperature, AT, for a given fixed input quantity of heat, 0,... 6} From the slope of the graph, calculate the specific heat, c of the blue block (Hint: See eqn. (3}). Notice that the fixed input quantity of heat is 0,1 = Pt, where P is the power [=400 W) and t is the time {= 5 minutes}. You need to convert the unit of time to seconds. Calculate c inj/KgC and convert the unit to Cal/KgC. Show calculation in the data sheet Brooklyn College 2 Questions 1. what flaws do you see in the assumption that the heat added to the water {or glycerin) is proportional to the time that the hotplate is on? 2. when heating water on a stove. a full pot of water would take longer to reach the boiling point than if the pot were halffull. Why? Data Sheet Name: Group: Date experiment performed: Part 1: Dependence of change in temperature, AT on quantity of heat input, Oh, for a given material and a given mass of object, In Table 1: To = 25C 6t (minutes) :1 (2,, (D T (\"(3) AT = T To (\"C) DDONIG'iU'l-FUJNI-'O 10 11 Is the graph of 6t (a: QR] versus AT a straight line? Part 2: Dependence of change in temperature, AT on mass of object, in for a given material and a given input of 0,, Table 2: To = 20C, fixed 0,, = 400 x 5 x 60 U) mass,m (kg) AT = T T (0C) Calculation of the slope of the graph of AT versus {l/m): Calculation of the specific heat. c, of the blue black, from the slope: U/KQOC] {Cal/K900 Answers to Questions: 1. 2