• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Hess's Law. The experiment conducted was meant to determine the enthalpy of formation of MgO(s) and CaO(s)

Extracts from this document...


Hess's Law Data Collection and Processing Table V: Heats of Formation Heat of Formation (kJ/mol) Substance Trial 1 Trial 2 Magnesium oxide - 101.5 � 0.5 - 81.1 � 0.5 Magnesium - 366.1 � 0.4 - 322.2 � 0.4 Calcium oxide N/A - 141.7 � 1.0 Calcium - 192.6 � 0.5 - 173.6 � 0.5 Notes: * The heats of formation were calculated using the formula ?H = Q/nlimiting reactant Ex: Magnesium oxide Trial 1: n(MgO) = (1.08 g � 0.01 g)/40.304 g/mol = 0.026796 mol n(HCl) = (100.0 g � 0.5 g)/36.461 g/mol = 2.7427 mol MgO 1 mol 0.026796 mol ����= ����� = ������������ H2O 1 mol 0.026796 mol HCl 2 mol 2.7427 mol ��� = ����� = ���������� H2O 1 mol 1.3714 mol Therefore MgO is the limiting reactant. Assuming HCl(aq) has the same density as water, the 100.0 mL of HCl(aq) has a mass of 100.0 g. Qsurr = mc?T = (100.0 g)(4.184 J/(g��C)(25.5�C - 19.0�C) = (100.0 g)(4.184 J/g��C)(6.5�C) ...read more.


+ 2HCl(aq) --> H2(aq) + MgCl2(aq) - 322.2 � 0.4 H2(g) + 1/2O2(g) --> H20(l) - 285.8 Table XI: Enthalpy of Formation of MgO Original Equation Enthalpy of Formation (kJ/mol) Mg(s) + 1/2O2(g) --> MgO(s) - 526.2 � 0.9 Table XII: Enthalpies of Reaction After Manipulating The Given Equations for CaO Manipulated Equation Enthalpy of Reaction (kJ/mol) CaCl2(aq) + H2O(l) --> CaO(s) + 2HCl(aq) 141.7 � 1.0 Ca(s) + 2HCl(aq) --> H2(aq) + CaCl2(aq) - 173.6 � 0.5 H2(g) + 1/2O2(g) --> H20(l) - 285.8 Table XIII: Enthalpy of Formation of CaO Original Equation Enthalpy of Formation (kJ/mol) Ca(s) + 1/2O2(g) --> CaO(s) - 317.7 � 1.5 Notes: * The enthalpy of formation was calculated by adding together the enthalpies of reaction Ex: Combustion of magnesium Trial 1: ?Hf = (101.5 - 366.1 - 285.8)kJ/mol = - 550.4 kJ/mol � 0.9 kJ/mol Error: 0.5 + 0.4 = 0.9 Table XIV: Enthalpy of Formation Averages Original Equation Average Enthalpy of Formation (kJ/mol) Mg(s) ...read more.


was determined experimentally. There were many sources of error that could have accounted for this. When the enthalpy of reaction for magnesium was calculated, the magnesium was first sanded with sandpaper to remove and magnesium oxide that had formed on it. Similarly, calcium oxide forms on calcium, however no attempt was made to remove the calcium oxide. This would mean that more moles of calcium were accounted for than were actually present, and that calcium oxide was also reacting but this was not recorded and the amount of calcium oxide was not measured. As is visible in Table VIII, the enthalpy of reaction of calcium is greater than that of calcium oxide. Since it was not all calcium and some calcium oxide reacting in the trial that was meant to be only calcium, the calcium oxide could be responsible for the enthalpy of reaction being lower than the accepted value. This difference between the magnesium and calcium experiments could be one source of error accounting for the large difference in percent error between the two. The experiment could be improved by sanding the calcium as well. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related International Baccalaureate Chemistry essays

  1. IB chemistry revision notes

    sulphur dioxide. o �B3 -->This molecule has one lone pair and three bond pairs. The lone pair creates a maximum repulsion. The shape it trigonal pyramidal. The bonds are polar, and because of the orientation of the bonds, the molecule is also polar. The bond angle is of ~107�.

  2. Experiment - The Empirical Formula of Magnesium Oxide

    Thus, the gradient of the scatter graph ought to be 1; though in the first graph the gradient is 0.6. After the elimination of the anomalous, the gradient became 0.7 which is closer to 1.0. It can be deduced that the off-true-value gradient was caused by some outlier points.

  1. Lab Experiment : The change in mass when magnesium burns. (Finding the empirical formula ...

    8. Less flame. 9. No flame but it glows. 10. Less sparks and less glow. 11.Little smoke. 12.No smoke(white fluid material and residue on lid). 13. No further reaction. Raw Data: Initial mass of crucible with lid ( in grams) + 0.0001= 27.6400g Mass of magnesium inside crucible with the lid ( in grams)

  2. Chemistry Lab. Deducing Enthalpy of Combustion of Magnesium Oxide with Hesss Law

    Temperature was recorded until the trend stabilized. The solution was then disposed. The same process was repeated with 0.5 g Magnesium Oxide and HCl. Variables: * Dependent: Temperature Change, Enthalpy Change * Independent: Reactants * Control: Room temperature, Time of recording temperature Raw Data: Table 1: Measurements recorded during reactions of MgO and Mg with HCl Reaction 1 (MgO)

  1. The aim of this experiment is to examine the enthalpy of combustion of the ...

    = ρ (H2O) * V (H2O) = 1.0 g cm-3 * 40.0 cm3 = 40.0 g The change in temperature is found in the following way : ΔT (H2O) = Tmin – Tmax = 24.0 °C – 50.0 °C = 26.0°C ΔT (H2O)

  2. To determine the standard enthalpy of formation of Magnesium Oxide using Hess Law.

    are as follows: 1. Mg (s) + 2HCl (aq.) ? MgCl2 (aq.) + H2 (g) ---------- ?HX 2. MgO (s) + 2HCl (aq.) ? MgCl2 (aq.) + H2O (g) ---------- ?HY 3. H2 (g) + O2 (g) ? H2O (l) ---------- ?HH2O = -285 kJ.mol-1 Adding all the three reactions, we obtained the following reaction: Mg (s)

  1. Discovering the formula of MgO

    Formula of magnesium oxide according to the theory of the charges of different ions: Furthermore, theoretical value is 40% since Mg which is in group 2 has a charge of +2 whereas oxygen which is in group 6 has a charge of -2, the charges are exchanged and cancelled out

  2. Bomb calorimetry. The goal of this experiment was to use temperature data over ...

    This step was necessary since the purpose of this experiment was to calculate the enthalpy of combustion of naphthalene, which could only be accomplished if the heat capacity of the vessel in which it was combusted was known. Figure 3 is a plot of the data obtained from the naphthalene combustion.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work