Validating Hesss law Essay Example for Free

Validating Hesss law EssayIs the atomic number 1 change for a given chemical change the same whether the reaction takes power in a single stage or via several stages, provided the initial and final conditions are the same.IntroductionHesss Law (1840) states that for a given chemical change the enthalpy change is the same whether the reaction takes place in a single stage or via several stages, provided the initial and final conditions are the same.We result turn out the validity of this law using the reaction between sodium hydroxide and hydrochloric unpleasant. The reaction between solid sodium hydroxide and dilute hydrochloric acid place be carried out in two ways.Method 1 NaOH(s) + HCl(aq) NaCl(aq) + H2O(l) ?H?1Method 2 NaOH(s) NaOH(aq) ?H?2then NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) ?H?3According to Hesss Law ?H?1 = ?H?2 + ?H?3In calculating the enthalpy of reaction values in from each one of the in a higher place and following cases, it is assumed thata. The density of the settlements is 1 gcm-3b. The specific heat capacity of the solutions is 4.2Jg-1K-1c. The specific heat capacity of the polystyrene cup is negligible and may be ignored.Apparatus* Polystyrene cup* Thermometer* HCl* NaOH pellets* H2O* Digital weight reader* Measuring cylinderMethod mensuration of ?H?1Pour 50cm3 of 1M hydrochloric acid into the polystyrene cup and reputation its temperature as accurately as you possibly can. Weigh out 2g of sodium hydroxide pellets and quickly add these to the acid in your polystyrene cup. Stir and record the maximum temperature reached. organise the enthalpy change of this reaction in kJmol-1.Measurement of ?H?2Pour 50cm3 of water into an empty polystyrene cup and record its temperature as accurately as you possibly can. Weigh out 2g of sodium hydroxide pellets and quickly add these to the water in your polystyrene cup. Stir and record the maximum temperature reached. Calculate the enthalpy change of this process in kJmol-1.Measurement of ?H? 3Pour 50cm3 of 1M sodium hydroxide into an empty polystyrene cup and record its temperature as accurately as you possibly can. Measure out 50cm3 of 1M hydrochloric acid into a measuring cylinder and record its temperature. Calculate the average initial temperature of the acid and the alkali. Add the acid to the alkali in your polystyrene cup and record the maximum temperature reached. Calculate the enthalpy change of this reaction inkJmol-1.Data CollectionMeasurement of ?H?1Measurement of ?H?2Measurement of ?H?3Initial Temperature/C ? 0.1CThe enthalpy change ?H?1 is given by multiplying the upsurge of HCl (m) by its specific heat capacity (Cp) and the change in temperature (?T). Since this reaction takes place in solution, which we assume to be mostly water. Hence the mass of the solution will be 50g and the specific heat capacity is given as 4.2J/g/C. The calculation for the mass of the solution is as follows% Error in ?T =The enthalpy change ?H?2 is given by multiplying the mass of NaOH (m) by its specific heat capacity (Cp) and the change in temperature (?T). Since this reaction takes place in solution, which we assume to be mostly water. Hence the mass of the solution will be 50g and the specific heat capacity is given as 4.2J/g/C. The calculation for the mass of the solution is as follows% Error in ?T =The enthalpy change ?H?3 is given by multiplying the mass of HCl (m) by its specific heat capacity (Cp) and the change in temperature (?T). Since this reaction takes place in solution, which we assume to be mostly water. Hence the mass of the solution will be 100g and the specific heat capacity is given as 4.2J/g/C. The calculation for the mass of the solution is as followsSo using the results found above we see thatIt can be seen that ?H?1 is almost equal to ?H?2 + ?H?3 but due to experimental errors a good deal(prenominal) as heat being lost to the surroundings and not having exact readings they are not equal. Hesss law has therefore been validated but the results would have been much more accurate if there was an insulating capsule around the polystyrene cup so as to prevent any heat from being lost to the environment and by having more accurate apparatus in terms of measuring cylinders and thermometers.