Thermochemistry: An Ice Calorimeter Determination of Reaction Enthalpy PDF

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Thermochemistry: An Ice Calorimeter Determination of Reaction Enthalpy Lab Report...

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Thermochemistry: An Ice Calorimeter Determination of Reaction Enthalpy Report by Austin Jones February 12th, 2020 Professor Paul Gilletti

Abstract: An ice calorimeter was used to study the reaction of magnesium metal and 1.00M sulfuric acid solution: Mg(s) +H2SO4(aq)  MgSO4(aq) + H2(g). With approximately 0.2416 g of Mg and 1.0057M of H2SO4, the experimental molar enthalpy of reaction was found to be ΔH = -326.2 kJ/mol at 0°C, 30.11% lower than the textbook value of ΔH° = -466.9 kJ/mol at 25°C.1

Introduction The first law of thermodynamics2, the Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred. Calorimeters are used to study heat transfer in a reaction and can help to determine if a reaction is exothermic or endothermic. This is done by measuring heat-induced temperature changes by a reaction in a calorimeter. In this lab, the heat transfer is isothermal meaning the temperature is constant throughout the entire reaction. Instead of measuring temperature change, we use and ice calorimeter and measure the change in volume throughout the reaction. The reaction Mg(s) +H2SO4(aq)  MgSO4(aq) + H2(g) is an exothermic reaction that will cause the ice to melt within the calorimeter. The volume of ice melted is recorded and used to calculate the enthalpy of reaction. Method No changes were made to the procedures in the lab manual3. An ice calorimeter was used with a fill tube, reaction test tube, and 1.000 mL pipet to record volume change. 0.2416 grams of Magnesium and 5.00 mL of 1.0057M Sulfuric Acid were used in the reaction. Volume was record at 30 second intervals before, during, and after the reaction. Reaction was initiated after 4 minutes of recorded volume. Sulfuric Acid was the limiting reactant with an excess of Magnesium at the end of the reaction. Experimental data was compared with theoretical data from the CRC handbook.

Results Table 1. Ice Calorimeter Data Time (s) 0 30 60 90 120 150 180 210 240 270 300

Pipet Vol. (mL) 0.850 0.840 0.832 0.829 0.821 0.818 0.810 0.807 0.800 0.777 0.715

Time (s) 330 360 390 420 450 480 510 540 570 600

Pipet Vol. (mL) 0.631 0.581 0.519 0.477 0.435 0.405 0.377 0.350 0.330 0.311

Fig. 1: Calorimeter Data

Time (s) 630 660 690 720 750 780 810 840 870 900

Pipet Vol. (mL) 0.295 0.281 0.270 0.258 0.248 0.239 0.230 0.224 0.216 0.210

Two linear trend lines are shown on Figure 1 for before and after the reaction to form two theoretically parallel lines in order to determine the pipet volume change throughout the reaction. Calculations Volume change for the melting of 1.000 gram of ice at constant temperature of 0°C 1.000 g Ice

mL =1.091mL |0.9164 g

1.000 g Liquid

mL =1.0001 mL |0.9999 g

1.091mL−1.0001 mL=0.009133 mL Change is pipet volume based on data on graph ΔV =0.70487 mL−0.25586 mL=0.44901 mL Mass of ice melted 0.44901mL

1.000 g =4.927 g Ice | 0.09113 mL

Quantity of heat (in Joules) generated by the reaction

|

4.927 g Ice 333 J =1641 J of RXN g Determine limiting reactant 0.2416 g Mg

1 mol Mg =0.009940 mols Mg |24.305 g Mg

| |

5.00 mL 1 kJ 1.0057 mols H 2 S O 4 =0.005029 mols H 2 S O 4 3 10 J 1 L H 2 S O 4 so l' n

Mole ratio is 1:1 based of the chemical equation Mg(s) +H2SO4(aq)  MgSO4(aq) + H2(g) thus H 2 S O4

is the limiting reactant

Enthalpy of reaction ΔH =

|

1641 J 1 kJ =−326.3 kJ /mol 0.005029 mols H 2 S O4 103 J

Percent difference based off the textbook value -466.9kJ/mol.1 kJ kJ −(−326.3 ) −466.9 mol mol difference= x 100=30.11 % kJ −466.9 mol Discussion According to the experiment, the reaction of Magnesium with Sulfuric acid is proven to be exothermic. The enthalpy of reaction was found to be -326.3kJ/mol for this experiment but was 30.11% off the standard enthalpy of reaction in the textbook. This could maybe be due to the 25°C temperature difference in the calorimeter, heat loss due to the reaction being conducted in an open test tube, system leaks, or other human error. Another big reason why calculations might be off can be due to that fact that there is no clear endpoint for the reaction in the data. In order to match the expected value of -466.9 kJ/mol, a volume change of 0.643mL would have needed to be observed compared to the 0.44901mL calculated from the experiment. This may have been the case if the reaction was recorded for a longer period and a different endpoint was determined.

References 1

“Appendix C: Thermodynamic Quantities for Substances and Ions at 25°C” in Darrell D.

Ebbing, Steven D. Gammon, General Chemistry, 9th ed., Houghton Mifflin, Boston, 2009, p. A10. 2

Boundless. Boundless Chemistry. https://courses.lumenlearning.com/boundless-

chemistry/chapter/the-laws-of-thermodynamics/ (accessed Feb 12, 2020). 3

Gilletti, Paul. CHM152LL Lab Manual Thermochemistry: An Ice Calorimeter Determination of

Reaction Enthalpy; Mesa Community College: Mesa, AZ, 2019....