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Dee Saenz Chem 1BL F 1 00 4 50 3 05 24 Experiment 10 Thermochemistry The purpose of this week s lab was to learn about temperature heat and heat capacity while also using a special tool called a calorimeter to find out how much heat certain reactions produce and measure the specific heat of a metal The objective of this lab was completed by following the steps accordingly and also doing multiple trials For this experiment we had to find the specific heat capacity of a calorimeter by determining the temperature of a water solution By using these data we were able to calculate the heat capacity of our unknown metal and the enthalpy values for multiple reactions A general method that I have used for this lab was leaving the lid of the calorimeter on since it reduces the amount of heat that can radiate in or out of the system resulting in more accurate results In part one of the lab we had to use a tool called a calorimeter which is used to measure the magnitude of the heat flow in a reaction The heat capacity of the calorimeter is determined since it is able to calculate accurately how much heat is being collected by the calorimeter as temperature is changing We figured out by measuring how much heat water is absorbed or given off when its temperature changes inside the calorimeter This number shows us how good the calorimeter is at holding onto or releasing heat when its temperature changes In the meantime of calculating the data we ran the calorimeter again to ensure that our first trial is had little to no errors For trial one the value for the heat capacity in the calorimeter 106 30 J C For trial two the value is 50 89 J C The average heat capacity is 78 60 J C For part two we had to sample an unknown metal to the nearest 0 01g in order to determine the specific heat capacity of the unknown metal We first had to prepare the metal to be heated so we carefully had to make sure it was completely dry Then the dry unknown metal was placed into a large test tube that has a loose topper on After these preparations we had to place this test tube into our designated hot water station which was in the very front of the room This solution had to remain in the boiling water for at least fifteen minutes to ensure the temperature of the metal reaches equilibrium with the temperature of the water The temperature of the metal was measured by getting 50 mL of distilled water and using a calorimeter in the solution alone to record the temperature change every thirty seconds for four minutes Then we added our boiling hot water and metal solution to our cup with a magnetic stir in it and had to record again every thirty seconds for three minutes The value of is 0 404 J g K According to the Law of Dulong and Petit the product of a metal s atomic mass M and its specific heat capacity is approximately equal to the molar heat capacity which is about 25 J mol K so in order to find we can use the formula So the molar mass of this unknown metal using this equation is 61 94 g mol To completely identify our unknown metal we had to look at three factors The value of our is 0 404 J g K and the two closest values were Ni 0 444 J g K and Zn 0 389 J g K The closest one is zinc For our second factor we compared our molar masses The molar mass of Nickel is 58 6934 g mol and the molar mass of zinc is 65 38 g mol And the molar mass of our unknown value is 61 94 allowing zinc to be more reasonable Lastly we were able to identify the metal by appearance For instance zinc was a very silvery and gray color which was very similar to our unknown metal The calculated mass had a value of 61 94 g mol while the actual was 65 38 g mol and a percent error of 5 26 The calculated value of was 0 404 J g K with a known value of 0 389 J g K and a percent error of 3 86 In part three a certain volume of water a certain amount of temperature and a certain were all measured to determine the heat of the reaction 4 3 4 3 4 3 mass of ammonium nitrate The way the temperature changes on the graph shows if the reaction gives off heat exothermic and makes the temperature go up or absorbs heat endothermic and makes the temperature go down Because our reaction is endothermic it means the system absorbs energy leading to the surrounding water having a lower temperature We were able to determine with the measured heat of the reaction with this given formula With this we calculated the amount of heat absorbed by the reaction to be 1299 80 J Using this we were able to find experimental to be 35 15 kJ mol compared to the calculated value being 28 6 kJ mol Lastly we had a percent error of 22 6 For part four the volume and molarity of a given strong acid and strong base were added to the calorimeter which resulted in the measurement of temperature change 2 We determined by using the formula With this we were able to get an experimental of 73 22 kJ mol a calculated value of 55 83 kJ mol and a percent error of 31 6 Throughout this experiment many calculations were presented with many formulas provided which could have resulted in multiple miscalculations etc That being said it is reasonable for there to be percent errors in general For our case since we did have some high numbered percent errors this can indicate that some major issues could have been during the actual experiment for instance maybe we have weighed something wrong or even added too much of a certain solution For instance during part four for the calculations I resulted in having a percent error of 31 6 for delta H hencing that our calculations for the experimental was significantly different from the calculated which could result in calculation error or just an error throughout the lab For trial one the value for the heat capacity in the calorimeter is 106 30 J C and 50 89 J C for trial two So as we can see there is another significant difference from these two values which is fairly off hencing the high percent error A given error for example if the hot metal was not completely dry before adding it to the calorimeter containing water the hot metal would affect the specific heat capacity of the metal by giving a wrong measurement and or wrong calculation for a certain mass which could ruin your calculations from the very beginning resulting in a high percentage percent error

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UCSB CHEM 1BL - Experiment 10: Thermochemistry

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