It is possible to measure the enthalpy change of combustion, ∆Hc, of ethanol, C2H5OH, using the following apparatus. [Figure 1.1] A student carries out an experiment to determine the value for ∆Hc of ethanol using the following instructions: • Weigh the spirit burner with ethanol and lid, record the starting mass to two decimal places. • Measure 100.00 cm³ of water and place it into the metal can. • Place a thermometer, with 0.1°C graduations, into the water and stir it, wait for 2 minutes. • Record the temperature of the water. • Light the wick and allow the flame to heat the water. • Continue to stir the water using the thermometer. • After the temperature has risen by approximately 20 °C place the lid on the flame to extinguish it. • Record the maximum temperature of the water. • Weigh the spirit burner and record the final mass. The student obtained the following results. initial temperature of water/°C | maximum temperature of water/°C | change in temperature of water, ∆T/°C | initial mass of spirit burner/g | final mass of spirit burner/g | mass of ethanol burned/g ---|---|---|---|---|--- 18.1 | 38.2 | | 153.29 | 152.76 |

1. (a)Complete the table. Record your answers to the correct number of decimal places.[1]
2. (b)Calculate the number of moles of ethanol burned. Give your answer to three significant figures. [A: C, 12.0; Η, 1.0; Ο, 16.0] moles of ethanol = ................................. [1][1]
3. (c)Use the formula q = mc∆T to determine the energy change, q, that took place during the experiment. Use q and your answer to (b) to calculate the enthalpy change of combustion of ethanol, ∆Hc, in kJ mol-1. Include a sign in your answer. 1.00 cm³ of water has a mass of 1.00g c = 4.18 J g-1 K-1 ∆Hc = ........................................ kJ mol-1 [2][2]
4. (d)Calculate the percentage error of the temperature change recorded in the table in (a). Show your working. percentage error = ................................. [1][1]
5. (e)State the effect, if any at all, on the accuracy of the experiment if the spirit burner was allowed to burn for longer. Explain your answer.[1]
6. (f)The flame was extinguished, but the lid of the spirit burner was not replaced immediately. Predict how this would affect the value of ∆Hc. Explain your answer.[2]
7. (g)(i)The value for ∆Hc of ethanol under standard conditions is –1367 kJ mol-1. Other than the reaction not being carried out under standard conditions, suggest two reasons why the value the student obtained in (c) is different from the actual value.[2]
8. (g)(ii)It is possible to calculate ∆Hc of ethanol using average bond enthalpies and the chemical equation for the reaction. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) Using average bond enthalpies, ∆Hc of ethanol is –1297 kJ mol-1. Explain why this value is different from the actual value for ∆Hc of ethanol under standard conditions.[1]

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