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.

Answer 1

0 Reaction (a) Mg = 0.5 g x 1 mole F 24.30 g = 0.0205 mole (b) Head absorbed by solution V= (s.h) solution * (me>>) Sojution X (17) solutia 3.1.0 (code x 100 () x 2 260) Tu solution 2200 cal T = 2.200 kcal) zo

(c) Hoi LAH a reaction reaction (ll- enou I kcal - x x 1000 Cal gram Mg ato atomic mass M2 1 male - - 2200, Cal 1 klal 24.30,2 0.5 g 1000 cal 3 Cal į mole = -106.92 Ko reactional AULO or are than reaction is exothermic

| Reaction (2) 1a Mgo = 1:0g x 1 mole 4o.30,g =0.0248 mole (b) as solletion ” a solution = (sh) solution X (mass) solution X(97) solution - 476 * 1 (%x 3 (*) Vsolution = 300 cal

(c) (on). reaction, 8*(2) Vreaction & 1 kcal & gram Myo 100o Cal Molar masy Mgo . I mole 2-300 Cal x 1 kcal x o 16oo cal - 40.30 g 1 mole (000 cal Svet2 (AH) (D ) reaction (2) = -12.02 kcal/meie (A) reaction (21 co or are so reaction is exothermic (A) reactional theoreticed = -11 kcal/mole % еко- 2 theoreticada experimental i theoretical s (-iai) - (-106- x 100 = 3.6756%

(AH) eaction as thosutical = -34.9 kcal/more 7 error = 1% error = 1(-34.9)-(-12.02) / xos -34.9 M100 = 65.5587 %

Д а оча) - - (o6 • 32 kla mole Ч. 18ч k1 1 kcal = 447.3532 kJ/moic In reaction (2) = -12.02 kcal Mole 4,184 A] I keed =-50.2916 kJ/mole