Background: The students were given full instructions on how to experimentally determine the enthalpy of reaction (ΔHrxn) for the combustion of magnesium ribbon, using Hess’s Law.
Data Collection:
| |Reaction 1 |Reaction 2 |
| |(MgO) |(Mg) |
| |Trial 1 |Trial 2 |Trial 1 |Trial 2 |
|Volume of 1.00 M HCl |50.0 mL ± 0.5 mL |50.0 mL ± 0.5 mL |50.0 mL ± 0.5 mL |50.0 mL ± 0.5 mL |
|Final temperature, t2 |28.9(C ± 0.1(C |28.8(C ± 0.1(C |44.8(C ± 0.1(C |44.4( C ± 0.1(C |
|Initial temperature, t1 |22.5(C ± 0.1(C |22.3( C ± 0.1(C |21.9(C ± 0.1(C |21.8( C ± 0.1(C |
|Mass of solid |0.50 g ± 0.01g |0.50 g ± 0.01g |0.25 g ± 0.01g |0.25 g ± 0.01g |
Data Processing:
| |Reaction 1 |
| |(MgO) |
| |Trial 1 |Trial 2 |
|Change in |final temperature – initial temperature |final temperature – initial temperature |
|temperature, (t |28.9(C – 22.5(C = 6.4(C |28.8(C – 22.3(C = 6.3(C |
| | | |
| |Uncertainty of temperature: 0.1(C + 0.1(C = 0.2(C |Uncertainty of temperature: 0.1(C + 0.1(C = 0.2(C |
| | | |
| |Change in temperature = 6.4(C ± 0.2(C |Change in temperature = 6.3(C ± 0.2(C |
|Heat of HCl |Mass of 1.0 M HCl [pic] specific heat of HCl [pic] change in |Mass of 1.0 M HCl [pic] specific heat of HCl [pic] change in |
|solution, q |temperature |temperature |
| | | |
| |To find mass of 1.0 M HCl : Density of 1.0M HCl [pic] volume |To find mass of 1.0 M HCl : Density of 1.0M HCl [pic] volume |
| |of 1.0M HCl |of 1.0M HCl |
| |1.005 [pic] [pic] 50.0 mL = 50.3 g |1.005 [pic] [pic] 50.0 mL = 50.3 g |
| | | |
| |50.3 g [pic] .00418 [pic] [pic] 6.4(C = 1.3 kJ |50.3 g [pic] .00418 [pic] [pic] 6.3(C = 1.3 kJ |
| | | |
| |% Uncertainty of Heat: [(0.5mL ÷ 50 mL) + (0.2(C ÷ 6.4(C)] |% Uncertainty of Heat: [(0.5mL ÷ 50 mL) + (0.2(C ÷ 6.3(C)] |
| |[pic] 100% = 4% |[pic] 100% = 4% |
| |Uncertainty of Heat: 4% of 1.3 kJ = 0.5 kJ |Uncertainty of Heat: 4% of 1.3 kJ = 0.5 kJ |
| | | |
| |Heat of HCl = 1.3 kJ ± 0.5 kJ |Heat of HCl = 1.3 kJ ± 0.5 kJ |
|Enthalpy change,|Enthalpy change of reaction = -heat of HCl solution |Enthalpy change of reaction = -heat of HCl solution |
|(H | | |
| |Enthalpy of MgO = -1.3 kJ ± 0.5 kJ |Enthalpy of MgO = -1.3 kJ ± 0.5 kJ |
|Moles of MgO |Mass of MgO ÷ molar mass of MgO |Mass of MgO ÷ molar mass of MgO |
| | | |
| |0.50 g MgO ÷ 40.30[pic] = 0.0120 mol |0.50 g MgO ÷ 40.30[pic] = 0.0120 mol |
| |% Uncertainty of moles: (0.01g ÷ 0.50g) [pic] 100% = 2% |% Uncertainty of moles: (0.01g ÷ 0.50g) [pic] 100% = 2% |
| |Uncertainty of moles: 2% of 0.0120 mol = 0.0002 mol |Uncertainty of moles: 2% of 0.0120 mol = 0.0002 mol |
| | | |
| |Moles of MgO = 0.0120 mol ± 0.0002 mol |Moles of MgO = 0.0120 mol ± 0.0002 mol |
|Molar enthalpy |Enthalpy of MgO ÷ moles of MgO |Enthalpy of MgO ÷ moles of MgO |
|change, (H/mol | | |
| |-1.3 kJ ÷ 0.0120 mol = -110 [pic] |-1.3 kJ ÷ 0.0120 mol = -110 [pic] |
| | | |
| |% Uncertainty: [(0.5 kJ ÷ 1.3 kJ) + (0.0002 mol ÷ 0.0120 mol)] |% Uncertainty: [(0.5 kJ ÷ 1.3 kJ) + (0.0002 mol ÷ 0.0120 mol)] |
| |[pic] 100% = 40% |[pic] 100% = 40% |
| |Uncertainty: 40% of -110 [pic] = 40 [pic] |Uncertainty: 40% of -110 [pic] = 40 [pic] |
| | | |
| |Molar enthalpy change = -110 [pic] ± 40 [pic] |Molar enthalpy change = -110 [pic] ± 40 [pic] |
|Average molar |(molar enthalpy change of Trial 1 + molar enthalpy change of Trial 2) ÷ 2 |
|enthalpy change |( -110 [pic] + -110 [pic] ) ÷ 2 = -110 [pic] |
| | |
| |Uncertainty: (40 [pic] + 40 [pic] ) ÷ 2 = 40 [pic] |
| | |
| |Average molar enthalpy change = -110 [pic] ± 40 [pic] |
| |Reaction 2 |
| |(Mg) |
| |Trial 1 |Trial 2 |
|Change in |final temperature – initial temperature |final temperature – initial temperature |
|temperature, (t |44.8(C – 21.9(C = 22.9(C |44.4(C – 21.8(C = 22.6(C |
| | | |
| |Uncertainty of temperature: 0.1(C + 0.1(C = 0.2(C |Uncertainty of temperature: 0.1(C + 0.1(C = 0.2(C |
| | | |
| |Change in temperature = 22.9(C ± 0.2(C |Change in temperature = 22.6(C ± 0.2(C |
|Heat of HCl |Mass of 1.0 M HCl [pic] specific heat of HCl [pic] change in |Mass of 1.0 M HCl [pic] specific heat of HCl [pic] change in |
|solution, q |temperature |temperature |
| | | |
| |To find mass of 1.0 M HCl : Density of 1.0M HCl [pic] volume |To find mass of 1.0 M HCl : Density of 1.0M HCl [pic] volume |
| |of 1.0M HCl |of 1.0M HCl |
| |1.005 [pic] [pic] 50.0 mL = 50.3 g |1.005 [pic] [pic] 50.0 mL = 50.3 g |
| | | |
| |50.3 g [pic] .00418 [pic] [pic] 22.9(C = 4.81 kJ |50.3 g [pic] .00418 [pic] [pic] 22.6(C = 4.75 kJ |
| | | |
| |% Uncertainty of Heat: [(0.5mL ÷ 50 mL) + (0.2(C ÷ 22.9(C)] |% Uncertainty of Heat: [(0.5mL ÷ 50 mL) + (0.2(C ÷ 22.6(C)] |
| |[pic] 100% = 1.9% |[pic] 100% = 1.9% |
| |Uncertainty of Heat: 1.9% of 4.81 kJ = 0.09 kJ |Uncertainty of Heat: 1.9% of 4.75 kJ = 0.09 kJ |
| | | |
| |Heat of HCl = 4.81 kJ ± 0.09 kJ |Heat of HCl = 4.75 kJ ± 0.09 kJ |
|Enthalpy change,|Enthalpy change of reaction = -heat of HCl solution |Enthalpy change of reaction = -heat of HCl solution |
|(H | | |
| |Enthalpy of Mg = -4.81 kJ ± 0.09 kJ |Enthalpy of Mg = -4.75 kJ ± 0.09 kJ |
|Moles of Mg |Mass of Mg ÷ molar mass of Mg |Mass of Mg ÷ molar mass of Mg |
| | | |
| |0.25 g ÷ 24.30[pic] = 0.010 mol |0.25 g ÷ 24.30[pic] = 0.010 mol |
| |% Uncertainty of moles: (0.01g ÷ 0.25g) [pic] 100% = 4% |% Uncertainty of moles: (0.01g ÷ 0.25g) [pic] 100% = 4% |
| |Uncertainty of moles: 4% of 0.0100 mol = 0.0004 mol |Uncertainty of moles: 4% of 0.0100 mol = 0.0004 mol |
| | | |
| |Moles of Mg = 0.0100 ± 0.0004 mol |Moles of Mg = 0.0100 ± 0.0004 mol |
|Molar enthalpy |Enthalpy of Mg ÷ moles of Mg |Enthalpy of Mg ÷ moles of Mg |
|change, (H/mol | | |
| |-4.81kJ ÷ 0.0100 mol = -481 [pic] |-4.75 kJ ÷ 0.0100 mol = - 475[pic] |
| | | |
| |% Uncertainty: [(0.09 kJ ÷ 4.81 kJ) + (0.0004 mol ÷ 0.0100 |% Uncertainty: [(0.09 kJ ÷ 4.75 kJ) + (0.0004 mol ÷ 0.0100 |
| |mol)] [pic] 100% = 6% |mol)] [pic] 100% = 6% |
| |Uncertainty: 6% of -481 [pic] = 29 [pic] |Uncertainty: 6% of -475 [pic] = 29 [pic] |
| | | |
| |Molar enthalpy change = -481 [pic] ± 29 [pic] |Molar enthalpy change = -475 [pic] ± 29 [pic] |
|Average molar |(molar enthalpy change of Trial 1 + molar enthalpy change of Trial 2) ÷ 2 |
|enthalpy change |(-481 [pic] + -475 [pic] ) ÷ 2 = -478 [pic] |
| | |
| |Uncertainty: (29 [pic] + 29 [pic] ) ÷ 2 = 29 [pic] |
| | |
| |Average molar enthalpy change = -478 [pic] ± 29 [pic] |
You May Also Find These Documents Helpful
-
Approximately 40 mL of the ionized water was added to the 100 mL beaker, then in a 10-mL graduated cylinder, 5-mL of HCl was measured then added to the 100-mL beaker of water. The 100 mL beaker was then placed on the assembled ring stand.…
- 529 Words
- 3 Pages
Good Essays -
3. Molarity of HCl = 5.26 x 10-3 mol / 0.010 L = 0.526 M…
- 561 Words
- 3 Pages
Satisfactory Essays -
To find this formula, a strip of Magnesium ribbon was burned in a crucible over a flame from a bunson burner. After the strip caught fire multiple times with the cover on, and 10 drops of distilled water were added, and the crucible was lightly heated. The crucible was then weighed and the mass recorded. Calculations were performed and the mole ratio of Mg to O was recorded. The results of other lab groups performing the same experiment were also recorded.…
- 408 Words
- 2 Pages
Good Essays -
QUESTION 2.2: Is the difference between the final and initial temperatures, T_f − 푇푖, positive or negative? Explain why you gave the answer you did.…
- 274 Words
- 2 Pages
Satisfactory Essays -
Assume all systems are at 25°C and all aqueous solutions are prepared with pure water unless otherwise indicated. Assume that ΔS°rxn and ΔH°rxn do not change appreciably with temperature.…
- 1497 Words
- 6 Pages
Satisfactory Essays -
Name: |Date:| Exp 10: Caloric Content of Food|| Your Data: |First Item|Second Item|Third Item| What Food are you using|||| |||| Mass of empty beaker|||| Mass of beaker and water|||| Net Mass of the water|||| |||| Initial mass of food and holder|||| Final mass of burnt food and holder|||| Net Mass of the burnt food|||| |||| Initial temp of the water|||| Final temp of the water|||| ∆ T in C (change in temperature)|||| Calculations: Show your numbers in the following calculation equations. First Item_________________ Heat (q) gained by the water ____J q = ΔT x mass of the water x (4.184 J/g˚C ) Where ΔT =…
- 279 Words
- 2 Pages
Satisfactory Essays -
In the appendix, show the equation used to determine the heats of reaction for reactions 1 – 6 and reactions 7 and 8.…
- 2516 Words
- 11 Pages
Good Essays -
2. Calculate the change in temperature T by substracting the average initial temperature from the final temperature of the mixture (T = Tf –Ti) Record in Data Table 1.…
- 777 Words
- 4 Pages
Satisfactory Essays -
4. Move the bottom 3 temperature dots (which are red) to the right (increasing the temperature), each about 10°C (one grid line).…
- 415 Words
- 2 Pages
Satisfactory Essays -
The purpose of the experiment is to calculate the enthalpy change occurring in the first of reaction of sodium hydroxide with hydrochloric acid and sodium hydroxide with ammonium chloride. Using Hess’ Law and the results for the enthalpy change of the first two reactions should give the enthalpy change of the third reaction of ammonia with hydrochloric acid.…
- 473 Words
- 2 Pages
Powerful Essays -
Our purpose of doing this lab was to prove the Hess’s law correct. Hess’s law suggests that the enthalpy change of a reaction must be equal to the sum of the enthalpy changes of the related reactions which lead to the original reactions. The following are the reactions at the lab;…
- 702 Words
- 3 Pages
Good Essays -
The purposes of these three experiments are to determine the heat capacity of a calorimeter and with that data, confirm Hess’s Law and observe enthalpy changes within reactions. By measuring the change in temperature that occurs with the interaction of two different reactants, we were able to determine both the calorimeter constant and the change in enthalpy of a given reaction. The results were rather mixed, as some numbers more closely resembled the theoretical values than others did.…
- 2337 Words
- 11 Pages
Good Essays -
T = 30 Cº (50Cº - 20Cº) (Change in temperaure. You only care about the hottest number since you are dealing with expansion.)…
- 679 Words
- 3 Pages
Satisfactory Essays -
Similar procedures are followed to determine the standard enthalpy of combustion of the rest of the alcohols. The results are tabulated in the table 3 Thus, all the 4 alcohols have been tested for their standard enthalpy of combustions. The overall results are as shown in a tabular form…
- 1344 Words
- 6 Pages
Powerful Essays -
The temperature variation is shown graphically in Figure 4.1. We observe that the limiting temperature is 700F.…
- 4964 Words
- 21 Pages
Powerful Essays