Calculation on the molar enthalpy change of a neutralization reaction Principle H2SO4(aq)+2NaOH(aq)=Na2SO4(aq)+2H2O(l) The reaction is a exothermic reaction, when the heat released by it is absorbed by water, the temperature of the water increases. The heat produced by the reaction can be calculated if it is assumed that all the heat is absorbed by the water. Heat change of reaction=-heat change of water =-mH2O×cH2O×△TH2O As the water has gained the heat produced by the reaction, the heat change of reaction is negative when the temperature of the water increases. As the heat change observed depends on the amount of reaction, for example the number of moles of fuel burned, enthalpy change reaction are usually expressed in kJmol-1. Chemicals Name of chemicals concentration Volume Water used for diluting Materials Name of materials Measuring cylinder Measuring cylinder Beaker Stirring rod Thermometer Balance Constant temperature tank stopwatch Safety goggle
Sulfuric acid 18 mol V-1 10ml 125ml
Sodium hydroxid 12 mol V-1 15ml 105ml
Condition 10 ml 100ml 50ml
Including poise Including plastic stir bar
Number of materials used 1 2 1 1 1 1 1 1 1
Procedures 1. Dilute both solutions H2SO4 and NaOH, from the given concentration to 1M and 2M. The volumes of the diluted solutions H2SO4 and NaOH with concentration 1M are 90ml which contains 0.09 moles H2SO4 and 60 ml which contains 0.06 moles NaOH respectively. And the volumes of the diluted solutions H2SO4 and NaOH concentration 2M are 45ml which contains 0.09 moles H2SO4 and 60 ml which contains 0.12 moles NaOH respectively. 2. Package the constant temperature tank. Insert the thermometer into the top of the tank with suitable height (ensure the thermometer cannot be touched the beaker’s bottom) . 3. As the coefficient of H2SO4 and NaOH is 1:2, so the ratio of amounts of H2SO4
4. 5. 6. 7.
and NaOH is 1:2. Pour 1M H2SO4 with volume of 30ml and 1M NaOH with volume of 60ml into the constant temperature tank, and then cover the top immediately. While the last step finished, record the time by using stopwatch for 180 seconds. And stir the solution by using stirring rod ceaselessly. Pour 2M H2SO4 with volume of 30ml and 2M NaOH with volume of 30 ml into the constant temperature tank, and then cover the top immediately. While the last step finished, record the time by using stopwatch. And stir the solution by suing stirring rod ceaselessly. Record the time until the temperature was almost constant (theoretically, temperature will fall to room temperature after the reaction is finished, but the insulation of the equipment is good so that the decreasing of temperature will marginally). Using the time recorded and the temperature changed as coordinate axis and draws a graph of the relationship between time and temperature.
Data collection The figure below is the time recorded and the temperature changed. When the concentration of sulfuric acid and sodium hydroxide are both 1M: Time 0 5 10 15 20 25 30 60 90 120 150 180 recorded(second) Temperature 18 21 24 26 28 29.5 29.5 29.5 29.1 29 28.8 28.7 changed(Celsius) The reaction was finished after around 25 seconds, so the temperature did not increase until 25 seconds. And when the conentration of sulfuric acid and sodium hydroxide are both 2M: Time 0 5 10 15 20 25 recorded(second) Temperature 18 23 27 31 33 35 changed(Celsius) 30 37 60 37 90 120 150 180 36
36.5 36.1 36
The reaction was finished after around 30 seconds, so the temperature did not increase any more until 30 seconds.
40 35 30 25 20 15 10 5 0 0 50
temperature VS time
From the figure above, it is easy to prove that it is an exothermic reaction. Calculation on molar enthalpy change: △Hsystem=0(assuming no heat loss) △Hsystem=△Hwater+△Hreaction(assuming all heat goes to the water) △Hreaction=-△Hwater For the exothermic reaction, △Hreaction is negative as heat has passed from...
References: Pearson Baccalaureate Standard Level Chemistry
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