# Lab 14 Heat of Reaction Objective: To experimentally determine the heat of reaction for two exothermic...

###### Question:

Lab 14 Heat of Reaction Objective: To experimentally determine the heat of reaction for two exothermic reactions. Consider the following equations. (1) Mg(s) + 2HCI → MgCl2(aq) + H2(g) Hz(8) AH = ? (2) MgO(s) + 2HCl(aq) → MgCl(aq) + HOH (1) AH2 = ? The reactions represented by equations (1) and (2) will be our experimental work for today. Background: The heat given off or gained in a reaction is commonly called the heat of reaction. A reaction that releases heat is exothermic: an endothermic reaction is one that absorbs heat. The heat given off or absorbed in a particular reaction system can be calculated if one knows the amount of material, the temperature change of the system and the specific heat of the material: q-mass x specific heal x (Tr-T). If the temperature increases, the last term, AT.is positive and q for the system is also positive. If the temperature of the system decreases, AT is negative and so is q. Since q depends directly on the mass of the material used, the heat (or enthalpy) of reaction, AHan is usually reported as energy/mol of reaction. AH can be calculated from experimental data: AH = q (kcal) / n (mole) where n is the number of moles of product or reactant used. Safety/Disposal: Always wear your safety goggles/safety glasses and follow safety procedures when performing experiments. 1. Magnesium powder, Mg: a serious fire hazard 2. Hydrochloric acid, HCl: highly corrosive; causes severe burns on eyes and skin contact and upon inhalation of vapors 3. Magnesium oxide: a skin and eye irritant; slightly hazardous in case of ingestion or inhalation Ceq.7 of 20.8°C PROCEDURE: Reaction (1): Reaction with Mg(s) 1. Add 100.0mL of 1.OM HCl solution to the calorimeter. 2. Assemble the calorimeter with the lid and stirrer in place and measure the temperature of the solution. Note the loop on the stirrer goes into the solution. Once the temperature has stabilized, record the initial temperature of the solutions to the nearest 0.1°C. 3. Weigh out 0.50g of Mg(s) in a tared weighing cup using a top-loading balance. The mass does not need to be exact, but must be recorded to the nearest centigram. 4. Add the Mg(s) to the calorimeter, cover with the lid and mix gently with constant stirring 5. Measure the temperature of the solution to the nearest 0.1°C. Record the highest temperature reached by the solution as the final temperature.
Reaction (2): Reaction with MgO(s) 1. Add 100.0mL of 1.OM HCl solution to the calorimeter. 2. Assemble the calorimeter with the lid and stirrer in place and measure the temperature of the solution. Note the loop on the stirrer goes into the solution. Once the temperature has stabilized, record the initial temperature of the solutions to the nearest 0.1°C. 3. Weigh out 1.00g of MgO(S) in a tared weighing cup using a top-loading balance. The mass does not need to be exact, but must be recorded to the nearest centigram. 4. Add the MgO(s) to the calorimeter, cover with the lid and mix gently with constant stirring 5. Measure the temperature of the solution to the nearest 0.1°C. Record the highest temperature reached by the solution as the final temperature.
Lab Partner's Name Bivo Lab 14 Heat of Reaction 30 DATA AND RESULTS Reaction (Mg) 1. Mass (g) 50 2. Tinitial) (°C) 3. T (final) (°C) 4. AT-Tr-T (C) 20.8 42.8 22 Reaction (2) ( MO) I gram 22.6 25.6 CALCULATIONS 1. Reaction (1) a. Using dimensional analysis, calculate the number of moles of Mg(s) used in the reaction. .509) Imole i mole mo 724.31 Imole 1 ig Calculate the heat absorbed by the solution using solution shsolution X solution X AT solution. Assume the density of the HCl solution is 1.00 g/mL to get mass of the solution. The specific heat (sh) of the solution is 1.00 calig C.
Because the system is well insulated we may assume that for the solution (quolution) is equal (in magnitude) but opposite (in sign) to reaction. So, qolutie- action. To calculate AH, in kcal/mol, we can say kcal Ikcal your grams Mg 1000 cal manice atomic mass Mg 1 mole mol Make sure you have the correct sign on your answer. You are calculating Areaction. Is the reaction exothermic or endothermic? Make sure the sign on AH is consistent with this. 2. Reaction (2) Using dimensional analysis, calculate the number of moles of MgO(s) used in the reaction. b. Calculate the heat absorbed by the solution using qolution shsolution X msolution X AT solution Assume the density of the HCl solution is 1.00 g/mL to get mass of the solution. The specific heat (sh) of the solution is 1.00 cal/g C.
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