Chemistry Lab report - Coursework Example

Building a Self-heating Cup: A Comparison of Two Exothermic Reactions Introduction Background Information A self-heating cup would allow you to heat food, coffee, or water without a stove, electricity, solar energy, or a flame. An exothermic reaction (usually, hydration of metal salts in water) provides the heat energy required. In the cup, the reactants are placed in separate compartments. A trigger on the cup allows you to heat the contents of the cup when required. On press of the trigger, the wall separating the reagents punctures and water reacts with the reagent to generate heat.

An average self-heating cup can raise water temperature from 20°C to 80°C and sustain the temperature for 40 minutes (Bargan Production Group).QuestionIn this lab, we aim to build a working model of a self heating cup using the heat released during an exothermic reaction. We shall also compare two chemical reactions to find which reactant causes water in the cup to reach higher temperature in a shorter duration. HypothesisIn the experiments, we assume that there is no heat loss during the reaction – the heat released during the reaction is equal to the heat absorbed by water in the cup.

The apparatus is open to the atmosphere and so pressure is constant throughout the reaction (Myers). VariablesIndependent variables: amount of calcium chloride in g, amount of copper sulfate + zinc in g, time of reaction is 10 minutes.Dependent variables: initial temperature of water in °C, final temperature of water in °C.Constant variables: Amount of water in the cup is 75 mL, temperature of the room is 21°C, humidity of the room is fixed, surface area of the beaker and plastic cup used in the experiment is the same.

MethodsApparatusDigital thermometer with a data logger, stop watch, 2 identical beakers, 2 plastic cups, 2 glass rods, weighing balance, aluminum foilReagentsReaction 1: tap water 75 mL, anhydrous calcium chloride 61.95 g, water 61 mLReaction 2: tap water 75 mL, zinc powder 4.8 g, copper sulfate 9.25 g, water 5 mLPrincipleIn our simulation of the self-heating cup, the heat energy from an exothermic reaction is used to heat water. Temperature of the water in the cup increases due to transfer of heat energy from the reaction to the cup through conduction.

If there is no heat loss during the experiment, Qwater = -Qreaction (Eq 1)Heat energy transferred to the water is calculated from the raise in water temperature (Myers):Qwater = mCΔT (Eq 2)Where, m is the mass of water, C is the specific heat capacity of water (4.186KJ/Kg°C), and ΔT is the change in water temperature.At constant pressure and volume, heat of reaction (heat energy released by the reaction) isΔE = Qreaction /n (Eq 3)Where n is the number of moles of reactant.ProcedureA plastic cup was covered with aluminum foil to prevent its melting on exposure to heat.

Tap water (75 mL) was added to the cup. To prevent heat loss from the cup, a lid made of aluminum foil was placed over the cup and two holes were made to the lid. Through one hole in the lid, a digital thermometer was placed to record temperature of water in the cup. The digital thermometer was connected to a data logger in order to record the temperature and to plot a temperature-time graph. A glass rod was placed through the other hole for stirring. The outer walls and bottom of a clean beaker were covered by aluminum foil in order to prevent heat loss during the reaction.

Anhydrous calcium chloride (61.95 g) was added to the beaker. Water to be added to the calcium chloride was measured (61 mL) and kept handy. Just before placing the cup on the beaker, the recording of temperature of water in the cup was started. Water was added to calcium chloride in the beaker and immediately, the cup was placed on the beaker, touching the solution. Temperature was recorded for 10 minutes, with constant stirring using the glass rod. The stirring is essential to ensure even heating of water in the cup.

A new cup and beaker were readied in a similar manner. To the new beaker, copper sulfate (9.25 g) and zinc powder (4.8 g) were added. When the apparatus was set up, 5 mL water was added to the zinc-copper sulfate mixture and the new cup was placed immediately on the beaker. Temperatures were recorded as earlier.A graph was plotted to show the temperature changes in both the reactions with time. At peak water temperatures, heat energy gained by water in the cups was calculated. Heats of reaction were then calculated.

Figure 1 Set up of a self-heating cupData CollectionTable 1 Variation of temperature of water in cups with timeTimes(s)Temperature (C)of water (Reaction 1: CaCl2 + H2O)Temperature (C)of water(Reaction 2: Zn + CuSO4 + H2O)018.98222.38432.118.95224.46364.420.50727.86196.721.97831.21412922.96732.817161.324.2634.93193.625.55336.217225.927.22737.14258.228.64737.383290.529.58538.209322.830.75338.597355.131.82138.889387.433.15739.034419.733.7438.8445234.56639.374484.335.39139.229516.636.14438.864548.936.60638.597582.637.06738.306Table 2 Peak temperature of water (75 mL) in self-heating cupsReaction ReactantActual mass g ± 0.

01 gAmount of water added to reactantInitial Temperature °CMax Temperature °CTime s1CaCl261.9561 mL18.98237.0675822CuSO4 + Zn9.25 + 4.8 5 mL22.38439.374452Graph 1Change in water temperature with time for Reaction 1 (CaCl2 + H2O) and Reaction 2 (Zn + CuSO4 + H2O)CalculationsReaction 1: In the beaker, calcium chloride dissolves spontaneously in water to release heat which is transferred to the water in the cup.Table 3: Qwater and Heat of reaction (ΔE) for Reaction 1 using Eq 1, Eq 2, and Eq 3.

CupTemperature increases from 18.982°C to 37.067°Cm = 0.075 KgC = 4.186 KJ/Kg°CΔT = 37.067°C-18.982°C = 18.175°CFrom Eq 2, Qwater = (0.075Kg ) × (4186 J/Kg°C) × (18.175°C) = 5.7 KJBeakerCaCl2 (s) + 2H2O (l)  CaCl2•2H2O (aq)From Eq 1,Qreaction = - Qwater = -5.7KJMass of CaCl2 = 61.95 gMolecular mass of CaCl2 = 110.98g/molMass of water = 61 gMolecular mass of water = 18 g/molNumber of moles of CaCl2 = (61.95g)/(110.98g/mol) = 0.558 molNumber of moles of water = (61 g)/(18 g/mol) = 3.33 mol0.558 moles of CaCl2 reacts with 1.

11 moles of water. From Eq 3,ΔE = -5.7KJ/0.558 mol = -10.21 KJ/molReaction 2: In the beaker, cationic single replacement of zinc in copper sulfate solution takes place to release heat, which is transferred to the cup.Table 4: Qwater and Heat of Reaction (ΔE) for Reaction 2 using Eq 1, Eq 2, and Eq 3CupTemperature increases from 22.384°C to 39.374°Cm = 0.075 KgC = 4.186 KJ/Kg°CΔT = 39.374°C – 22.384°C = 16.99°CFrom Eq 2, Qwater = (0.075Kg ) × (4.186 KJ/Kg°C) × (16.99°C)= 5.33 KJBeakerCuSO4 (aq) + Zn (s)  Cu (s) + ZnSO4 (aq)From Eq 1,Qreaction = - Qwater = -5.

33KJMass of Zn = 4.8 gMass of CuSO4 = 9.25 gAtomic mass of Zn = 65.4 g/molMolecular mass of CuSO4 = 159.6 g/molNumber of moles of zinc = 4.8g/65.4 g/mol = 0.073 molNumber of moles of CuSO4 = 9.25 g/159.6 g/mol = 0.058 mol0.058 moles of Zn reacts with 0.058 moles of CuSO4 to from ZnSO4From Eq 3, ΔE = -5.33 KJ/0.058 mol = -92 KJ/molInterpretation of resultsTable 1 and Graph 1 show an increase in water temperature with time. This increase occurs as the reactions progress. Data for Reaction 2 indicates that the temperature of water reaches a peak, and then begins to decrease.

At this point, the reaction is complete. Tables 3 and 4 show that Qreaction and Heat of reaction are negative for both Reaction 1 and Reaction 2, indicating exothermic reactions, where heat is released.ConclusionAn exothermic reaction provides heat energy required to heat contents of a self-heating cup. In the self-heating cup designed in the laboratory, we could heat water using two such exothermic reactions: 1) hydration of calcium chloride; and 2) cationic single replacement of zinc in aqueous copper sulfate solution.

Results show that temperature gain is greater in the hydration of calcium chloride and the heat energy released during this reaction is greater. So the exothermic reaction of hydration of calcium chloride is a more efficient source of fuel in the self heating cup. Error AnalysisThe heat of hydration of calcium chloride is -81.33 KJ/mol (Thermochemistry: Heat of Solution). This implies,ΔE = -81.33 KJ/molFor Reaction 1 which was assumed to occur under constant pressure and volume, Eq 3 becomesQreaction = (-81.33 KJ/mol) × (n mol)Assuming there is no loss of heat to the beaker walls or to the atmosphere, heat energy absorbed by the water according to Eq 1 is Qwater = -Qreaction = (81.33 KJ/mol) × (n mol)Change in water temperature according to Eq 2 is ΔT = Qwater/mc= [(81.33 KJ/mol) × (0.558 mol)]/[(0.075 Kg) × (4.

186 KJ/Kg°C)] = 144.5°CAlternatively, considering the observed change in temperature (ΔT = 18.175°C),n = mcΔT/(81.33 KJ/mol)= [(0.075 Kg) × (4.186 KJ/Kg°C) × (18.175°C)]/ (81.33 KJ/mol)= 0.07 molSo, mass of CaCl2 required to generate the observed ΔT = (0.07 mol) × (110.98 g/mol) = 7.78 gThis could be due to one of the two reasons - either the hydration of calcium chloride was not completed or some of the heat energy generated during the reaction was lost.Works Cited"Bargan Production Group." BPG. 6 Feb. 2009 .Myers, Richard.

The Basics of Chemistry (Basics of the Hard Sciences). New York: Greenwood Press, 2003. ."Thermochemistry: Heat of Solution." Science in Motion. 6 Feb. 2009 .