Energy of Phase Changes Jayme Bartz Group Members: Tommy, Kari, and Erica Section 226 Kasun ImaduwageIntroduction: The purpose of our Energy of Phase Changes lab was to use the temperature change of water, it’s mass, and specific heat to determine the heat associated with different phase changes. Specific heat is an element’s heat capacity. Water and ice were used in finding the heat of fusion, the change from a solid to a liquid. Water and liquid Nitrogen were used in finding the heat of vaporization, the change from a liquid to a gas. And water and dry ice were used in finding the heat of sublimation, the change from a solid to a gas. All of these phase changes were endothermic because they all released energy instead of absorbing it. The energy transferred, as heat, was discovered using variations of this basic equation. Q(heat) = m(mass)*s(specific heat)*T (temperature change) Heat gained = - heat lost Experimental: The procedure for this experiment was found from the course website. For Part 1, a time probe was set up in conjunction with the Chemistry with Vernier file 18. Four Styrofoam cups were retrieved, labeled, nested, and then their mass was recorded. 250 mL of water was then heated to between 55-65 degrees Celsius. 60 mL of the water was put into one cup and the mass was recorded. Then, the second cup was placed on the balance and 20 mL of ice was measured. The temperature of the first cup was taken then the ice from cup 2 was poured in. The probe was placed in the calorimeter until all of the ice had melted. This process was repeated three times. The average value of the heat fusion was then found as well as the molar heat of fusion. The same procedure was repeated in Parts 2 and 3, except for a change in the contents of cup 2. In Part 2, 40 mL of liquid nitrogen was used and in Part 3, 15 g of dry ice was used. Results: The equation used to determine the heat of fusion in Part 1 was: [mass(s)* mass(s)*specific* Mass(l)*specific*T] The equation used to determine the heat of vaporization in Part 2 and the heat of sublimation in Part 3 was: [mass(s)*H] = - [mass(l)*specific*T] The average heat of fusion was 4563.41j/mol. The molar mass of water, 18.01 g, was used to change it from j/g. The average heat of vaporization was 6501.94 j/mol, and the molar mass of N2, 28.02, was used to convert it from j/g. The average heat of sublimation was 27,579.77 j/mol, and the molar mass of dry ice, 44.01, was used to convert it as well.Table 1. Part 1 Results Quantity Trial 1 Trial 2 Trial 3 m[H2O(l)] 57.77 g 57.78 g 58.45 g m[H2O(s)] 19.99 g 20.05 g 20.00 g Ti[H2O(l)] 50.50 C 58.00 C 50.00 C Tf[H2O(l)] 19.00 C 24.10 C 19.70 C ChangeT[H2O(l)] -31.50 C -33.90 C - 30.30 C Table 2. Part 2 Results Quantity Trial 1 Trial 2 Trial 3 M[H2O(l)] 56.67 g 56.29 g 59.98 g M[NO(l)] 40.02 g 40.03 g 40.02 g Ti{H2)(l)] 50.00 C 61.00 C 52.00 C Tf[H2O(l)] 13.55 C 18.48 C 15.32 C Changet[H2O(l)] -36.45 C -42.52 C -36.68 C Table 3. Part 3 Results Quantity Trial 1 Trial 2 Trial 3 M[H2O(l)] 56.98 g 56.08 g 57.32 g mCO2(s)] 14.99 g 14.98 g 15.02 g Ti[H2O(l)] 52.50 C 64.00 C 61. 00 C Tf[H2O(l)] 14.46 C 22.06 C 22.29 C ChangeT[H2O(l)] -38.04 C -41.94 C -38.71 C Table 4. Calculated results. Trial 1 Trial 2 Trial 3 H(fus) 4480.60 j/mol 4809.71 j/mol 4391.93 j/mol H(vap) 6051.20 j/mol 7009.69 j/mol 6444.93 j/mol H(sub) 26625.90 j/mol 29811.30 j/mol 27202.10 j/mol Discussion: Our strategy with this experiment was to get our temperature measurements as accurate as possible so that we could account for almost all of the energy released in the phase changes. Each person was responsible for a specific part (ie. the water in cup 1) because we knew after running nine trials we could get sloppy and therefore decrease the accuracy of our measurements. All of the phase changes that we studied today were endothermic in nature because they released energy while they were moving down to lower densities. If we had, for example, studied a phase change of a liquid to a solid, the change would be exothermic because the change would require an absorption of energy from its environment. Our goal to find calculate the heat released in each trial was met. The numbers are all in a range for each Part. We were expecting the heat of sublimation to have the highest amount oftransferred energy because going from a solid to a gas is technically two phase changes and would release almost twice as much energy. But we underestimated because the heat released during sublimation was almost five times as much as was released in the other two changes. The impact of the intermolecular forces could have had something to do with this, however. Intermolecular forces are the forces between molecules that determine the physical properties of states of matter. In the case of these experiments, the intermolecular forces between the water molecules decreased because the heat produced and released was providing the molecules with enough energy to overcome the forces. The likely sources of error in this experiment would be from calculating the change in temperatures. We were unaware that. One assumption that we can make from this experiment is that if sublimation releases the most energy, then a phase change from a gas to a solid would absorb more energy than a change from a liquid to a solid. One likely source of error was in our temperature readings and our calculations. Even if we got the data right, a simple algebraic mistake could have altered the average. For the temperature in Part 1, we were supposed to have the initial temperature of the melted ice be 0 degrees Celsius. Instead we used the temperature of the hot water cup. Because the initial temperature was wrong, the change in temperature was wrong which is a vital part of the equation so the whole average is invalid. In the future it would be wise to understand were the values are coming from so that we don’t just assume we know which is the initial, final, and so on. Conclusions: The overall goal of this experiment was to determine heats relationship to the energy in phase changes. The experiment was approached with great caution in regard to the collecting of accurate temperatures between the phase changes. The average heat of fusion was found to be 4563.41 j/mol, the average heat of vaporization 6501.94 j/mol, and the average heat of sublimation was 27,579.77 j/mol. It is concluded from