Heat of Solidification Lab-Writeup

Introduction In chemistry, substances require a certain amount of energy in the form of average kinetic energy (temperature) to freeze. To reach the temperature a substance requires to freeze, it must lose a certain amount of heat energy (a form of energy transferred from one object to another, because of a temperature difference). When a substance reaches its freezing point and begins to freeze, its temperature remains constant until it is completely frozen.

However, in order to melt a substance must go through a energy change, creating the problem, “What energy changes occur when a liquid solidifies? ”. To solve the problem, a hypothesis was proposed, stating “When a substance begins to solidify, it releases heat energy, because a substance must reach its heat of solidification (heat required to freeze) by losing a certain amount of heat, in order to solidify”. In order to test this hypothesis, a experiment was performed. Materials and Methods

In the experiment, the materials required were 1 wax sample in a test tube with the weight of the test tube labeled, a 250 mL beaker, a ringstand, a wire gauze, a graduated cylinder, a Bunsen Burner, a styrofoam calorimeter, and a thermometer. To perform the experiment, first the calorimeter was filled with 100 mL of water using a graduated cylinder, and the temperature of the water was found and recorded. Next, the beaker was filled 3/4 full with water and placed on the stand of the ringstand above a gently burning flame from the Bunsen Burner.

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Then, the mass of the test tube and wax was found and recorded, and the tube was placed in the beaker. After the wax in the tube melted, the tube was placed in the calorimeter, using a wire gauze. Lastly, once the wax in the tube solidified, the temperature of the water in the calorimeter was measured and recorded. Results Data Recorded During Experiment Mass wax and test tube41. 2 gramsTemperature water after heating26 ? C Mass empty test tube21. 0 gramsTemperature water before heating16 ? C Mass wax20. 2 gramsTemperature change10 ? C

Volume water used100 mLMass of water used100 grams In the data table above, the mass of the wax was found by subtracting the mass of the empty test tube from the mass of the wax and test tube, giving an answer of 20. 2 g. To find the volume of water used, the mass of the water was multiplied by the density of the water, giving an answer of 100 g. To find the temperature change of the water, the temperature of the water after heating was subtracted by the temperature of the water before heating, giving an answer of 10 ? C. Calculations

After the experiment, the heat gained by the water from the wax in the calorimeter was calculated using the formula q = mC? T, where C equaled 4. 18 J/g * ? C. After the corresponding values were plugged in, the equation: 100g(4. 18 J/g * ? C. )(26? C-16? C) was created and solved for an answer of 4180 J of heat gained. After the amount of heat gained was found, the heat released per gram of wax (heat of solidification) was calculated using the equation: 4180 J/20. 2g, giving an answer of 206. 93 J released per gram of wax.

Although the heat released per gram of wax, found through the calculations, was 206. 93 J, the accepted value was 150. 0 J/g, because of this, the percent error was calculated using the formula:(measured - actualactual)100. After the values were plugged in, giving the equation:(206. 93 J/g - 150. 0 J/g150. 0 J/g)100, the percent error was found to be 38%. Discussion After the results were found, a conclusion was drawn up supporting the hypothesis. In the experiment, the temperature of the water increased from 16 ? C to 26 ? C after the wax solidified.

This showed that the wax must have released heat energy, in order to cause the temperature of the water to change, due to temperature requiring heat to change. In a experiment, there are many different possible sources of scientific error. In the experiment that was preformed, two possible sources of error were determined. The first source of error found was, the thermometer may have miss-measured the temperature of the water after the wax solidified, too high or low, which would have caused the heat of solidification to be too high or low.

The other source of error was the wax may not have fully solidified, which would have made the heat of solidification too low, due to the wax not fully releasing its heat energy. To better understand the experiment that was preformed, summery questions were asked. The first question asked was, “The heat of combustion of wax is 45,000 J/g. Explain why there is such a large difference between the heat of solidification and heat of combustion in terms of the type of change”.

To answer the question, a response was made: “Due to the heat of combustion of wax being the heat released from the chemical reaction between oxygen and wax, it is a chemical change and because the heat of solidification of wax is a physical change and chemical changes release a significantly larger amount of heat then physical changes, the heat of combustion of wax releases a much larger amount of heat”. The second question asked was “The amount of heat released by the solidifying was is equal in magnitude to the amount of heat that the wax absorbed when it melted.

Explain why this is so in terms of the arrangement of molecules in liquids vs. solids”. To respond to this question the response: “In order to change the arrangement of molecules from a solid to a liquid state, the wax must absorb a certain amount of heat and in order to return to a solid state, it must release the energy it absorbed. In the last question, the following was asked: “Predict the effect of the change in the mass of the wax used or volume of water in the calorimeter on the following parameters.

Assume all variables remain constant other then the one listed. If twice the amount of wax or half the amount of water was used in the experiment, how would the temperature, heat absorbed by the water and the calculated heat of solidification change. Explain your predictions for the heat of solidification”. In the answer responding to the question, it was stated, “both the temperature and heat absorbed by the water would increase, however the heat of solidification would stay the same, due to the wax continuing to release the same amount of heat per gram of wax.

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