Guided Notes and Practice- Topi 5.1: Calorimetry and Enthalpy Calculations

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1 Name: Date: Pd: Guided Notes and Practice- Topi 5.1: Calorimetry and Enthalpy Calculations Endothermic vs. Exothermic 1. Label each ΔH value as being exothermic or endothermic. Thermochemical Equations 2. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) ΔH = -890 kj mol -1 What is the heat released when 32.0g of oxygen is burned? (Ans. -445kJ) Calorimetry q = mc ΔT Specific Heat of a Metal 3. How much heat is released when 10.0g of Copper with a specific heat of0.385 Jg -1-1 is cooled from 85.0 to 25.0? (Ans. -231J) Combustion 4. Calculate the enthalpy of combustion of ethanol from the following data. Assume all heat from the reaction is absorbed by the water. (Ans kJ mol -1 ) a. Compare your value with the IB Data Booklet value and suggest reasons for any difference.

2 Combustion 5. When g of ethanol was burned, it produced a temperature rise of 15.7 K in 275 g of water. a. Draw the calorimetry set-up. b. Write the ΔH c reaction. c. Calculate the ΔH for the reaction. (-1050kJ mol -1 ) d. The date book value is kj mol -1. Include 3 reasons for the discrepancy. Reaction in Solution cm 3 of mol dm -3 copper (II) sulfate was placed in a polystyrene cup. After 2 min, 1.20 g of powdered zinc was added. The temperature was taken every 30 seconds and the following graph was obtained. Calculate the enthalpy change for the reaction taking place. (Ans kj mol -1 ) T 0 = Initial temp of reactants = 17 T 1 = Highest temp actually reached = 26.5 T 2 = Temp that would have been reached if no heat were lost to the surroundings = 27.4.

3 a. Why was there a wait time in the beginning? b. Copper (II) sulfate solution is blue. Zinc sulfate solution is colorless. Zinc is a silver-grey metal and copper is a reddish brown metal. Stat what you would think you would observe as the reaction proceeds. c. What are three assumptions you have made in arriving at your answer? d. The literature value is -218 kj mol 1-. Comment on the validity of your assumptions you stated. Neutralization cm 3 of 1.00 mol dm -3 hydrochloric acid was added to 50.0 cm 3 of 1.00 mol dm -3 sodium hydroxide solution in a polystyrene beaker. The initial temperature of both solutions was After stirring and accounting for the heat loss, the highest temperature reached was Calculate the enthalpy change for the reaction. (Ans kj mol -1 )

4 Constant Volume Neutralization 8. The experiment involves the neutralization of sodium hydroxide with sulfuric acid to form water and sodium sulfate. Assumptions: The NaOH and H 2 SO 4 are 1M (1 mol dm -3 ) The total volume is kept constant at 120 cm 3 with varying volumes of NaOH and H 2 SO 4 No heat is lost from the system All heat is transferred to the water Assume 120 cm 3 of solution contains 120 cm 3 of water Evaluate the following when the temperature changes are measured when different volumes of NaOH and H 2 SO 4 are mixed. a. Determine the volumes of the solutions which produce the largest increase in temperature. b. Calculate the heat produced by the reaction when the maximum temperature was produced. (Ans kj) c. Calculate the heat produced for one mole of NaOH. (Ans kj mol -1 ) d. Calculate the % error and suggest a reason for the discrepancy between the experimental and literature values. The literature value at standard conditions is kj mol -1. (Ans. 7.30%)

5 Extra Practice Specific Heat Capacity 1. How much heat is needed to raise a 0.30 kg piece of aluminum from 30.0 to 150.0? The specific heat capacity of aluminum is 0.900Jg (Ans. 32.4kJ) 2. Calculate the temperature change when 1960 J of heat are added to g of Copper. The specific heat capacity of copper is 0.386Jg (Ans K) 3. Calculate the specific heat of the unknown metal x 10 4 J of energy are added to g of the unknown metal. The temperature raises from 38.7 to (Ans J g -1-1 ) 4. Calculate the final temperature if 200.0J of heat is added to a 50.0 g sample of mercury at The specific heat capacity of mercury is Jg (Ans ) Exothermic and Endothermic Diagrams 1. Sketch the diagram for each of the following reactions. Label as endothermic or exothermic. a. N 2 (g) + O 2 (g) 2NO (g) ΔH = +181 kj b. PCl 3 (g) + Cl 2 (g) PCl 5 (g) ΔH = kj

6 Calorimetry 1. Determine the specific heat capacity of an unknown metal from the following information g of metal with an initial temperature of 99.2 is placed in cm 3 of water with an initial temperature of The temperature of the water raises by 3.3. (Ans J g -1-1 ) q= mcδt q H2O = -q metal ΔT = T f -T i water C p = Jg g of water at 15 is mixed with 67.3 g of water at 89.2 and allowed to come to equilibrium. After some time, the temperature stops changing. What is the final temperature of the mixture? (Ans. 69 ) 3. How much energy in kj must be removed from 225g of water in order to lower its temperature from 25.0 to 10.0? (Ans. 14.1kJ) 4. A calorimeter is used to measure the enthalpy of combustion of paraffin wax by burning a candle to heat a sample of water. The following data was collected. Initial Mass of Candle Final Mass of Candle Mass of Water Initial Temperature of Water Final Temperature of Water 24.7 g 23.6 g g

7 a. If the chemical formula of paraffin wax is C 22 H 46, use the data to determine the molar enthalpy of combustion of paraffin wax. (Ans x 10 3 kj mol -1 ) b. Based on the enthalpy of combustion of paraffin, what mass of paraffin must be burned in order to heat 2.00L of water from 20.0 to 100.0? (Ans g) 5. A calorimeter was used to determine the molar enthalpy of solution of AlCl 3. When a sample of AlCl 3 was dissolved in water the following data were collected. Mass of AlCl 3 (g) Mass of H 2 O (g) Initial Temp ( ) Final Temp( ) Determine the molar enthalpy of solution of AlCl3. (Ans: -373 kj/mol) 6. The combustion of methanol is represented by the following chemical equation: 2CH 3 OH(l) + 3O 2 (g) --> 2CO 2 (g) + 4H 2 O(l) If the enthalpy of combustion for this reaction is kj answer the following: a. How much energy would be liberated by the combustion of 10.5 g of methanol? (Ans: 238 kj)

8 b. How much energy would be liberated if 3.75 g of water are produced in this reaction? (Ans: 75.5 kj) c. What mass of methanol must be burned in order to heat g of water from 20.0 to 95.5? (Ans: 6.98 g) 7. When 13.4g of ammonium chloride is mixed with 2.00x10 2 g of water it dissociates into ions and causes the temperature of the solution to drop from 20.0 to a. Determine the molar enthalpy of solution for ammonium chloride. (Ans: +15.7kJ mol -1 ) b. Write the thermochemical equation for the reaction. c. Sketch the enthalpy diagram for the above reaction