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experiment Hess Law

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Introduction

Name : Mohd Haziq Al-Hakim Bin Hamirruddin Class : M08F Date : 9 July 2009 Practical : 16 Data Collection and Processing Part A:- Mass of magnesium ribbon = 0.2836 � 0.0001g Volume of 0.5 M of HCl = 50.0 � 0.5 cm3 Reactant Initial Temperature, � 0.5�C Highest Temperature, � 0.5�C Mg + HCl 27.0 40.5 Table 1 shows the initial and highest temperature for reaction between Mg and HCl To calculate the change in temperature, the following equation will be used:- Reactant Change in Temperature, � 1.0�C Mg + HCl 13.5 Table 2 shows the change in temperature for reaction between Mg and HCl Equation for part A:- Mg (s) + 2HCl (aq) --> MgCl2 (aq) + H2 (g) Mole of magnesium Mole of hydrochloric acid = mass = MV RMM 1000 = 0.2836 g = 50.0x0.5 24.3 1000 = 0.0118 mol = 0.025 mol Thus, ...read more.

Middle

30.0 Table 3 shows the initial and highest temperature for reaction between MgO and HCl To calculate the change in temperature, the following equation will be used:- Reactant Change in Temperature, � 1.0�C MgO + HCl 2.0 Table 4 shows the change in temperature for reaction between MgO and HCl Equation for part B:- MgO (s) + 2HCl (aq) --> MgCl2 (aq) + H2O (l) Mole of magnesium oxide Mole of Hydrochloric acid = mass = MV RMM 1000 = 0.4985g = 50x0.5 (24.3+16) 1000 = 0.0124 mol = 0.025 mol Thus, the limiting reagent is magnesium oxide Calculation: Heat change, Q = mc?T = 50g � 4.2 Jmol-1�C-1 � 2 �C = 420 J ?Hrxn = -420_ 0.0124 = -33.87 kJmol-1 Uncertainties: Mass = = 1.0 % Temperature = = 50.0 % No of mole = = 8.1% Total = 59.1% ?Hrxn = -33.87 kJmol-1 � 59.1 % Since the reactions are exothermic, the ?Hrxn for each reaction is negative. ...read more.

Conclusion

+ 2HCl(aq) � MgCl2(aq) + H2(g) ?Hrxn = -240.25 kJmol-1 � 9.25% MgCl2(aq) + H2O(l) � MgO(s) + 2HCl(aq) ?Hrxn = +33.87 kJmol-1 � 59.1% Mg(s) + H2O(l) � MgO(s) + H2(g) ?Hrxn = -206.38 kJmol-1 � 68.35% ?Hrxn = -206.38 kJmol-1 � 16.12 % For the theoretical value: 1. Mg(s) + (g) MgO(s) ?Hrxn = -601.8 kJmol-1 2. H2(g) + (g) H2O(l) ?Hrxn = -285.8 kJmol-1 By reversing equation 2: 3. H2O(l) H2(g) + (g) ?Hrxn = +285.8 kJmol-1 The theoretical value of the reaction, equation 1 + equation 3: Mg(s) + (g) MgO(s) ?Hrxn = -601.8 kJmol-1 H2O(l) H2(g) + (g) ?Hrxn = +285.8 kJmol-1 Mg(s) + H2O(l) MgO(s) + H2(g) ?Hrxn = -316.0 kJmol -1 ?Hrxn obtained from this experiment = -206.38 kJmol-1 The theoretical value of ?Hrxn = -316.0 kJmol -1 Percentage error = Theoretical value - Experimental value Theoretical value = = 34.69% Reference: Chemistry: A Central Science by Brown, Le May and Bursten ...read more.

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