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

Using Hess's law to calculate enthalpy change

Extracts from this document...

Introduction

Chemistry lab report (5) Using Hess law to calculate enthalpy change Aim: To calculate the enthalpy change for the reaction of: (MgSO4(s) + 7H2O MgSO4.7H2O(s) ) Hypothesis: The literature value according to research is -104 Kj/mol Variables: Dependant variable: The final temperature of the solution Independent variable: --------------------------------- Controlled variables: - Mass of water - Mass of magnesium sulphate anhydrous - Mass of MgSO4.7H20 Materials: 1) Safety spectacles 2) 2 filter papers 3) Spatula 4) Digital balance 5) 2 polystyrene cups 6) Thermometer 7) Magnesium sulphate anhydrous 8) Magnesium sulphate-7- water 9) Distilled water 10) Measuring cylinder Procedure: Part A 1) Weigh 3.01g of MgSO4 anhydrous to the nearest 0.01g on a filter paper, using the digital balance. 2) Weigh 45.00g of water to the nearest 0.01g into a polystyrene cup using the balance. 3) Measure the initial temperature of the measured amount of water using the thermometer and record this value. 4) Add the measured amount of MgSO4 anhydrous to the water and stir. Measure and record the maximum temperature obtained using the thermometer. Part B 1) ...read more.

Middle

Number of moles of water = mass / molar mass = 45.1 / 18.0 = 2.50 moles *Number of moles of MgSO4(s) = Mass/ Molar mass = 3.02 / (24.31 + 32.06 + (4 x 16.00)) = 3.02 / 120 = 0.0251 moles * Ratio of moles = 1 : 100 Thus both reactants are limiting * Enthalpy change = Q / number of moles = 603 / 0.0251 = - 24023.90 (rounded to 3 significant figures) = -24000 J/mol (Exothermic reaction) Enthalpy change for part B: (MgSO4.7H20(s) + 93H2O(l) MgSO4(aq,100H2O)) * Q = m x c delta T * M = 6.19 + 41.9 = 48.09 (rounded to 3 significant figures) = 48.1 g * C = 4.18 J/g.K * Delta T = 16 - 18 = - 2 K (place only the absolute value) = 2.00 Q = 402.116 (rounded to 3 significant figures) = 402 J * Number of moles of water = mass / molar mass = 41.9 / 18.0 = 2.33 moles *number of moles of MgSO4.7H2O = mass / molar mass = 6.19 / (24.31 + 32.06 + (4 x 16.00) ...read more.

Conclusion

x 100 = 0.313 % Total percentage uncertainties = 0.166 + 0.0808 + 0.0111 + 0.0119 + 0.278 + 0.238 + 0.278 + 0.313 = 1.3768 = 1.38 % The enthalpy change = - 40 � ((1.38/100) x 40) = - 0 � 0.552 Kj/ mole Conclusion: Percentage error: difference between calculated value and literature value divided by literature value times 100 Percentage error = ((40 - 104) / - 104) x 100 = (- 64 / 104) x 100 = 61.5 % (take absolute value) Sources of error: 1) Heat lost to the surrounding 2) The specific heat capacity used in calculations was that of water, not the mixture itself 3) Parallax error 4) Position of thermometer 5) Stirring was not constant Improvements: 1) Use a well insulated vessel with lid 2) Find the specific heat capacity of the mixture itself 3) Use digital thermometer connected to a computer 4) Ensure that the line of sight is perpendicular to the reading of the thermometer and measuring cylinder 5) Use magnetic stirrer for uniform stirring 6) Repeat the experiment several times, taking an average value for the heat emitted or gained by the mixture ...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. hess's law

    Graph 1 showing the Change in Temperatures when hydrated copper (II) sulphate was added to water [Temperature against Time]: Graph 2 showing the Change in Temperatures when anhydrous copper (II) sulphate was added to water [Temperature against Time]: Data Processing and Presentation: Molar Mass of CuSO4 = 159.5 g Molar Mass of CuSO4 .

  2. Enthalpy Change Design Lab (6/6)How does changing the initial temperature (19C, 25C, 35C, and ...

    and HCl(aq) should also be held constant throughout the investigation, across all variations of temperature, and trials. By doing so, the number of moles of KOH(aq) and HCl(aq) that react can be effectively controlled during the investigation. This is important to control because if the number of moles of HCl(aq)

  1. Thermodynamics: Enthalpy of Neutralization and Calorimetry

    These calculations also include uncertainty and the propagation thereof. All the results for trial 1 and the rest of the trials are placed in charts at the end. Note: whenever s is used below, it represents specific heat. Heat Capacity of Calorimeter Mass of Cold Water 49.951 (�.001)g -7.781(�.001)g 42.170 �.001 g Mass of Hot Water 95.928 (�.001)g -

  2. Enthalpy and Hess law

    Using stopwatch and thermometer the change in temperature was recorded. For the second route, 4g of NaOH was weighed. Then to form 2M of NaOH, 50 ml of water was added. A thermometer and stopwatch was used to monitor the change in temperature.

  1. Hesss Law Lab, use Hesss law to find the enthalpy change of combustion of ...

    Once again, I recorded all changes observed during the course of the reaction. VARIABLES Independent: � Type of chemicals used � Amount of chemicals used Dependant: � Change in enthalpy Controlled: � Elevation � Air pressure � Room temperature � Equipment � Humidity OBSERVATIONS Qualitative Hydrochloric acid solution It was a transparent water like solution.

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

    = 26.0 K Knowing this , we can calculate the total amount of energy that has been transformed to water : Q = 40.0 g * 4.20 J g-1 K-1 * 26 K Q = 4368 J = 4.36 kJ Mass of Methanol used in experiment : m (CH3OH)

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

    The strips were weighed each time on the same electronic balance and each time, the mass of Magnesium was approximately the same. 2. Mass of Magnesium Oxide (For part Y): For all trials, 0.05g of MgO was weighed out using the same electronic balance.

  2. The chemistry of atmospheric and water pollution.

    + O2 (g) This bromine oxide radical reacts with an oxygen free radical to form a bromine free radical and oxygen: BrO. (g) + O. (g) ï Br. (g) + O2 (g) Like the chlorine free radical produced, the bromine free radical is free to destroy thousands of ozone molecules.

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