Energy changes

This question is about temperature changes. A student investigated the change in temperature of a solution when different masses of ammonium nitrate were dissolved in water. <br/><br/> This is the method used. <br/><br/> 1. Measure 200 cm3 of water into a polystyrene cup. <br/><br/> 2. Measure the temperature of the water. <br/><br/> 3. Add 4.0 g of ammonium nitrate to the water. <br/><br/> 4. Stir the solution until all the ammonium nitrate has dissolved. <br/><br/> 5. Measure the lowest temperature reached by the solution. <br/><br/> 6. Repeat steps 1 to 5 with different masses of ammonium nitrate. <br/><br/> Give the independent variable and the dependent variable in the investigation. <br/><br/> Independent variable: ____________ <br/><br/> Dependent variable: ______________

Plot the data from Table 6 on the graph paper. Draw a line of best fit.<br/><br/>**Table 6**<br/><br/>| Mass of ammonium nitrate (g) | Lowest temperature (°C) <br/><br/> <div style="font-family: sans-serif; max-width: 600px;"> <table style="width: 100%; border-collapse: collapse; border: 1px solid black; text-align: center;"> <thead> <tr style="background-color: #f9f9f9;"> <th style="border: 1px solid black; padding: 12px;">Mass of ammonium nitrate added in grams</th> <th style="border: 1px solid black; padding: 12px;">Lowest temperature of solution in °C</th> </tr> </thead> <tbody> <tr><td style="border: 1px solid black; padding: 10px;">4.0</td><td style="border: 1px solid black; padding: 10px;">18.2</td></tr> <tr><td style="border: 1px solid black; padding: 10px;">8.0</td><td style="border: 1px solid black; padding: 10px;">16.2</td></tr> <tr><td style="border: 1px solid black; padding: 10px;">12.0</td><td style="border: 1px solid black; padding: 10px;">15.2</td></tr> <tr><td style="border: 1px solid black; padding: 10px;">16.0</td><td style="border: 1px solid black; padding: 10px;">13.6</td></tr> <tr><td style="border: 1px solid black; padding: 10px;">20.0</td><td style="border: 1px solid black; padding: 10px;">12.4</td></tr> <tr><td style="border: 1px solid black; padding: 10px;">24.0</td><td style="border: 1px solid black; padding: 10px;">10.6</td></tr> </tbody> </table> </div>

Determine the initial temperature of the water. You should extend your line of best fit on the graph.

How do the results show that dissolving ammonium nitrate in water is endothermic?

The student repeated the experiment for 8.0 g of ammonium nitrate three more times. The student recorded the mean lowest temperature as 16.5 ± 0.3 °C. Explain why the student included ± 0.3 °C after the mean lowest temperature. <div style="font-family: Arial, sans-serif; max-width: 700px;"> <h3 style="text-align: center;">Table 7</h3> <table style="width: 100%; border-collapse: collapse; text-align: center; border: 1px solid black;"> <thead> <tr> <th style="border: 1px solid black; padding: 10px; width: 30%;"></th> <th style="border: 1px solid black; padding: 10px;">Trial 1</th> <th style="border: 1px solid black; padding: 10px;">Trial 2</th> <th style="border: 1px solid black; padding: 10px;">Trial 3</th> <th style="border: 1px solid black; padding: 10px;">Trial 4</th> <th style="border: 1px solid black; padding: 10px; font-weight: bold;">Mean</th> </tr> </thead> <tbody> <tr> <td style="border: 1px solid black; padding: 10px; font-weight: bold; text-align: left;">Lowest temperature of solution in °C</td> <td style="border: 1px solid black; padding: 10px;">16.2</td> <td style="border: 1px solid black; padding: 10px;">16.6</td> <td style="border: 1px solid black; padding: 10px;">16.8</td> <td style="border: 1px solid black; padding: 10px;">16.4</td> <td style="border: 1px solid black; padding: 10px; font-weight: bold;">16.5</td> </tr> </tbody> </table> </div>

What type of error is shown by the results in Table 7?

A student investigated the energy change of the reaction between zinc and copper sulfate solution. The method and results are shown. Draw two lines of best fit on Figure 3. The lines should cross.

Explain the results shown in Figure 3. Do not refer to anomalous points. Use data from Figure 3.

Explain why using a polystyrene cup gives more accurate results than using a glass beaker.

The results show random errors. The student did not make any measuring errors. Suggest one reason for the random errors in this experiment.

Propane reacts with oxygen to produce carbon dioxide and water. The reaction is exothermic. Figure 8 shows four reaction profiles. Which is the correct reaction profile and labels for the reaction between propane and oxygen?

Figure 9 shows the displayed formula equation for the reaction between propane and oxygen. The overall energy change of this exothermic reaction is 2219 kJ/mol. Table 4 shows the bond energies of the bonds in the reaction. Calculate the bond energy of the C-H bond (X). <br/><br/> <table border="1" cellpadding="10" cellspacing="0" style="border-collapse: collapse; font-family: Arial, sans-serif; font-size: 14px; border: 2px solid black;"> <caption style="font-weight: bold; font-size: 16px; margin-bottom: 10px;">Table 4</caption> <tr> <th style="border: 1px solid black; padding: 10px;"></th> <th style="border: 1px solid black; padding: 10px; text-align: center;">C — C</th> <th style="border: 1px solid black; padding: 10px; text-align: center;">C — H</th> <th style="border: 1px solid black; padding: 10px; text-align: center;">O = O</th> <th style="border: 1px solid black; padding: 10px; text-align: center;">C = O</th> <th style="border: 1px solid black; padding: 10px; text-align: center;">O — H</th> </tr> <tr> <td style="border: 1px solid black; padding: 10px; font-weight: bold;">Energy in kJ/mol</td> <td style="border: 1px solid black; padding: 10px; text-align: center;">347</td> <td style="border: 1px solid black; padding: 10px; text-align: center; font-weight: bold;">X</td> <td style="border: 1px solid black; padding: 10px; text-align: center;">498</td> <td style="border: 1px solid black; padding: 10px; text-align: center;">805</td> <td style="border: 1px solid black; padding: 10px; text-align: center;">464</td> </tr> </table> <br/><br/>

What does the symbol ⇌ mean?

Figure 2 represents the reaction profile of the catalysed reaction between ammonia and oxygen. Complete the reaction profile for the catalysed reaction in Figure 2. You should: • label the activation energy • label the reactants and products, using the names of the reactants and products.

How would Figure 2 be different if no catalyst was used?