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Chemistry 12
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Name________________
Partner________________ Date________________ Purpose: Compare; Heat of combustion and heat of solidification. Enthalpy -Endothermic and Exthermix- What energy is needed? Introduction: By adding energy, meteria could be formed to another form. Basicly, if solid is heated up, it would be liquid(liquefaction). And if liquid is heated up, it would be gas(Vaporization). Also if gas is heated down, it would be liquid(liquefaction), and liquid would be solid(Solidification). Between those action, what energy would be needed? The Heat of Combustion of Candle wax is determined in part A and compared to the heat of solidification of candle waz in part B. Since amounts of heat cannnot be measured directly, they are measured indirectly in this experiment by their effect on a mesured mass of water comtained in a tin-can calorimeter. We have seen that 4.2 joules of heat added to 1 gram of water raises the temperature of the water 1C. (Science 10) Therefore, the quantity of heat absorbed by the water in the calorimater can be calculated by using the following formula: or Q = mC_T You will need to use fire on this experiment, so concentrate your attention on it. Maku sure do not tumble the candle. And do not put paper or textbook near the fire. Fire might catch something. Materials are comparatively low price but do not waste. Apparatus and Materials:
Procedure: Part A. Combustion of Wax
1. Cheack materials. Make sure you have all and there is no materials that have trouble. 2. Light the short candle and drop its wax on a base. And put the candle on it and cool down. (therefore candle does not move easily. 3. Weigh the candle and the base to the nearest tenth of a gram, and cheack the combine mass. 4. Take The cold water and cheack its mass and tempture. 5. Put fire on Candle and heat the water. 6. Blow out the candle when you think the temperture of the water is as far above room temperature. 7. After blowing out the candle, stir the water in the calorimeter for 20 or 30 secounds, then read the final temperture. 8. Reweight the candle with its base. Including the drappings. Record the mass. Part B. Freezing of candle wax
9. Prepare hot water. 10. Obtain a test tube one third to one half full of candle wax. 11. Determine the weight of an empty 18 X 150mm test tube. 12. Using a test tube holder, place the test tube containing the candle wax into the beaker of water being heated. Keep heating until all the wax is melted. 13. Remove the test tube from the beaker and wait. 14. Place 150 mL of water and a thermometer in your calorimeter. The water should be 2 or 3 Degrees elsius below room temperture. 15. Dry off the test tube, and watch it until the sides ot bottom just begin to freeze. Read the water temputure and immerse the test tube containing the wax in the water. 16. Watch the test tube until the wax has completely solidified. Then remove the test tube from the calorimeter, and read the final water temperature. 17. Return Apparatus and Materials, and clean up. Data Table:
Observations: See the last pages. Conclusion: From this experiment, we knew that Heat of Combustion needs more energy than Heat of solidification. This is because burning(Obtain) is a chemicak change (+O2) and a freezing is a physical change, and chemical change needs more energy to break up molecule. Therefore, Heat of Combustion(chemical change) needs more energy than Heat of solidification(physical change).
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