Specific Heat Capacity

Lab 5: Specific Heat of Metals
INTRODUCTION
System: is that part of the universe on which attention is focused.
Surroundings: exchange energy with the system and makes up, in principle, the rest of the universe. State properties: The state of a system is described by giving its composition, temperature and pressure.
Heat energy transfer has the symbol q, and falls into two categories:
endothermic process (q > 0 i.e. q is positive) when heat flows into the reaction system from the surroundings;
exothermic process (q < 0 i.e. q is negative) when heat flows out of the reaction system into the surroundings. q = C × Δt where Δt is change in temperature (Δt = tfinal – tinitial) C is the heat capacity of the system. This is the amount of heat required to raise the temperature of the system 1°C and has the units of J/°C. The heat transfer is measured in joules (J) or kilojoules (kJ). Another unit used is the calorie, which is the amount of energy required to change the temperature of 1 gram of water 1°C. where c is specific heat capacity, defined as the amount of heat required to raise the temperature of one gram of substance 1°C: 1 cal/(g・°C). = 4.184 J/(g・°C). m is the mass in grams. The specific heat of water is 4.184 J/(g・°C). Metals have a lower specific heat: cFe = 0.44 J/(g・°C) cCu = 0.34 J/(g・°C) cAl = 0.90 J/(g・°C). A calorimeter is an instrument for determining the amount of heat evolved, transferred or absorbed. In our case it will consist of a closed insulated vessel with a thermometer. When two different substances of different initial temperatures are introduced into the calorimeter, they exchange heat and both reach the equal final temperature. In this experiment we will measure the specific heat of several metals by warming them to a known temperature and adding them to a known quantity of water in a calorimeter and measuring the resulting (final) temperature. Heat is transferred between the heated metal and the water, such that the heat loss by the metal is equal to (but opposite in sign) the heat gained by the water in the calorimeter. qMe = - qwater Using this, we can determine the specific heat of an unknown metal from the following equation: mMe cMe ΔtMe = - (mwater c water Δtwater) The specific heat capacity of metal, cMe, can also be used to determine the atomic weight of a pure metal by using the law of Dulong and Petit: MMe . cMe ≈ 6 (cal/mol.°C) where MMe is atomic weight of metal [g/mol]. PROCEDURE Go to the stock room by clicking on the calorimeters label. Find Cu in the metals’ cabinet and bring it to the lab bench. Place the Cu on the balance and record the weight. Place the Cu in the oven. Click on the oven door to open. Once the Cu is inside, click on the door to close. Be sure that the oven reads 100oC. Use the up and down arrows to adjust the temperature if necessary. Return to the stock room and select the coffee cup. Bring it to the lab bench and place it by the ring stand. Do not remove the lid. Fill the 100 ml graduated cylinder with water then pour the water into the coffee cup. 6. Click the temperature probe. Click the green light to begin stirring (you should see the shaft rotating). Click graph then save in the thermometer window. Allow 20-30 seconds to obtain a baseline water temperature. 7. Remove the Cu from the oven and place it in the coffee cup. Do not remove the coffee cup lid before adding the copper. Continue recording for 20-30 seconds after the maximum temperature is reached. You may click on the accelerator button on the back wall to speed up the process. Click stop on the thermometer window to stop recording. A data link will appear in your lab book. 8. Repeat the procedure for Fe, Al, and one other metal of your choosing. Be sure to write down the identity of this metal. Unknown 9. Repeat the experiment one more time using an unknown. Click on unknowns in the stockroom. Once in the stockroom, click unknowns again. Select “Metals” from the list that appears.

Last Completed Projects