Enthalpy Change Of Neutralization(1).docx

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Chemistry SL/HL: Determining enthalpy change of neutralization

Enthalpy change of neutralization is enthalpy change when 1 mol of water is formed as acid and base react in standard condition. Enthalpy change of neutralization is always exothermic (the value is negative). It means neutralization reactions always give out heat to the surrounding causing the increase of temperature of the surrounding. When measuring the enthalpy change of neutralization, the energy released by the reaction is absorbed by the surrounding, which is the solution, hence increases the temperature of the solution. It is expressed in this equation: Qneutralization = Qsolution. Qneutralization is the energy released by the neutralization reaction; and Qsolution is the energy absorbed by the solution where the reaction takes place. Today we will try to understanding the principle in measuring and calculating the enthalpy change of neutralization through practical application: determining the enthalpy change of neutralization between an acid and an alkali.

Determining the enthalpy change of neutralization between HCl and NaOH. Procedures: 1. Using measuring cylinder take 50.0 ml of HCl 1.0 mol dm-3 and put into a 250 ml beaker glass. 2. Using a thermometer, measure the temperature of the acid. Record your data. 3. Take 50.0 ml of NaOH 1.0 mol dm-3 using measuring cylinder and then put into a 50 ml beaker glass. Measure the temperature of the alkali and take note. 4. Prepare a calorimeter with its insulation. 5.

Put the acid into the calorimeter and measure the temperature of the acid. Record your data.

6. Put the thermometer inside the calorimeter and then put the NaOH solution into the calorimeter. 7. Stir the mixture with thermometer and observe the highest temperature reached. Record your data.

Calculating the enthalpy change of neutralization between HCl and NaOH A. Calculate the Qsolution = mass of solution x specific heat capacity of solution x Tsolution 1. What is the mass of the solution? 50mL HCL and 50 mL NaOH

2. What is the specific heat capacity of the solution? 4.184 J/gram celcius

3. What is the temperature change of the solution? 26.81 - 20 = 6.81 celcius

Put all those values into the formula above and calculate the Qsolution. What is the Qsolution? Q = 100 x 4.184 x -6.81 = 2842.4 J/oC

B. Qneutralization = Qsolution. What is the Qneutralization? This is the amount of heat released by the reaction of HCl and NaOH. Using the definition of enthalpy change of neutralization above, what do you need to do next to find the value of the enthalpy change of neutralization between HCl and NaOH?

a. Find mole of water form in reaction

HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O (l) Mole of water = 0.05mol

b. Find Q of 1 mol of water 2849.3/0.05 = -56986 J = -56.986 kJ/mol

C. The accepted value for Hneutralization of HCl and NaOH is -58.0 kJ/mol. Compare the value from the experiment and the accepted value. Suggest possible reasons for the difference between the accepted value and the value from the experiment. Because of the apparatus may not insulate the solution well. (58-57)/58 x 100% = 1.7%

Chemistry SL/HL: Determining enthalpy change of solution

Enthalpy change of dissolution is the enthalpy change when 1 mol of solute is dissolved in excess solvent to give a solution with “infinite dilution.” Infinite dilution is a state when in a solution all solute’s particles are surrounded by the solvent’s particles. In other words, there is no interaction between the particles of the solutes. Enthalpy change of solution can be exothermic or endothermic. The basic principle in measuring the enthalpy change of solution is the amount of energy released or taken in during the dissolution process equals to the amount of heat absorbed or given out by the surrounding, which is the final solution: Qdissolution = Qsolution In this activity we will try to measure and calculate the enthalpy change of dissolution of two different compounds: ammonium nitrate Procedures: 1. Prepare 200 ml of distilled water and put into a calorimeter with its insulation. 2. Measure the temperature of the water and record your data. 3. Weigh 1.0 gram of NH4NO3 and put into the water. Stir the water to ensure complete dissolution of NH4NO3 and record the temperature of the solution. Calculating the enthalpy change of dissolution of NH4NO3 A. Calculate the Qsolution = mass of solution x specific heat capacity of solution x Tsolution 4. What is the mass of the solution? 200ml

5. What is the specific heat capacity of the solution? 4.18 J/g celsius

6. What is the temperature change of the solution? 0.38 celsius

Put all those values into the formula above and calculate the Qsolution. What is the Qsolution? Q = 200 x 4.18 x 0.39 = 317.98 J

B. Qdissolution = Qsolution. What is the Qdissolution?

This is the amount of heat taken in as NH4NO3 dissolves in water. Using the definition of enthalpy change of dissolution above, what do you need to do next to find the value of the enthalpy change of dissolution of NH4NO3? a. Find mole of NH4NO3 dissolved Mol= mass/mr = 1/80.06 = 0.0125 mol

b. Find Q/mol = 3.17.98/0.0125 = 25438 J/mol = 25.4 KJ/mol

C. The accepted value for Hdissolution of NH4NO3 is +25.4 kJ/mol (http://pulse.pharmacy.arizona.edu/resources/heatofsolution.pdf). Compare the value from the experiment and the accepted value. Suggest possible reasons for the difference between the accepted value and the value from the experiment.