CHE 210 - General Chemistry I (Lab) - Textbook
- LAB 1 (Weeks 1 & 2) Introducing Measurements in the Laboratory
- LAB 2 (Week 3) The Density of Liquids and Solids
- LAB 3 (Week 4) Nomenclature of Ionic Compounds
- LAB 4 (Week 5) Chemical Formlua Determination
- LAB 5 (Week 6) Types of Reactions
- LAB 6 (Week 7) Mole Ratios and Reaction Stoichiometry
- LAB 7 (Weeks 8 & 9) Titration of Vinegar
Learning Outcomes
Attribution.
- LAB 9 (Week 11) Determination of the Gas Constant
- LAB 10 (Week 12) Gravimetric Analysis of an Unknown Sulfate
- LAB 11 (Weeks 13 & 14) Spectrochemistry
Attribution & Licensing
Chem 210 general chemistry 1.
Compiled by Nelson Nunez-Rodriguez
Conditions of Use:
- Measure enthalpy values of reactions - const. P calorimetry
- U se Hess’s Law to determine the enthalpy of combustion of a metal
Click on the links below for Lab 8, Calorimetry and Hess's Law
- Calorimetry and Hess's Law
- Prelab Assignment: Calorimetry and Hess's Law
- Lab Report: Calorimetry and Hess’s Law
Calorimetry and Hess’s Law, Online Chemistry Lab Manual. Authored by: Physical Sciences Department, Santa Monica College. Located at: https://drive.google.com/file/d/1Sccw6C-tXqqlEoFVC8xgNc8gmMB09WxK/view Attribution: CC BY-NC 4.0
Prelab Assignment: Calorimetry and Hess’s Law, Online Chemistry Lab Manual. Authored by: Physical Sciences Department, Santa Monica College. Located at: https://drive.google.com/file/d/1yqO2MXeCkLnSCgaB0ogJMutGSpp4nV-y/view?usp=sharing Attribution: CC BY-NC 4.0
Lab Report: Calorimetry and Hess’s Law, Online Chemistry Lab Manual. Authored by: Physical Sciences Department, Santa Monica College. Located at: https://drive.google.com/file/d/1BXEmdwfjAmh-68Mloo2VzCz3JrgXRgs5/view?usp=sharing Attribution: CC BY-NC 4.0
Chem 11 Lab - Instructions . Authored by: Physical Sciences Department, Santa Monica College. Located at: https://sites.google.com/view/smcchemistry/chemistry/chem-11-experiments?authuser=0 Attribution: CC BY-NC 4.0
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Shop Experiment Additivity of Heats of Reaction: Hess’s Law Experiments
Additivity of heats of reaction: hess’s law.
Experiment #18 from Chemistry with Vernier
Introduction
In this experiment, you will use a Styrofoam-cup calorimeter to measure the heat released by three reactions. One of the reactions is the same as the combination of the other two reactions. Therefore, according to Hess’s law, the heat of reaction of the one reaction should be equal to the sum of the heats of reaction for the other two. This concept is sometimes referred to as the additivity of heats of reaction . The primary objective of this experiment is to confirm this law.
The reactions we will use in this experiment are:
(1) Solid sodium hydroxide dissolves in water to form an aqueous solution of ions.
(2) Solid sodium hydroxide reacts with aqueous hydrochloric acid to form water and an aqueous solution of sodium chloride.
(3) Solutions of aqueous sodium hydroxide and hydrochloric acid react to form water and aqueous sodium chloride.
In this experiment, you will
- Combine equations for two reactions to obtain the equation for a third reaction.
- Use a calorimeter to measure the temperature change in each of three reactions.
- Calculate the heat of reaction, ΔH, for the three reactions.
- Use the results to confirm Hess’s law.
Sensors and Equipment
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Correlations
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Lab Report: Experimental Verification of Hess's Law
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In this experiment, we aimed to validate Hess's Law by calculating the heat of reaction using coffee cup calorimeters. We investigated the reactions involving NaOH, aqueous NaOH, and hydrochloric acid. The heat generated during the dissociation of NaOH was determined to be -47.2 kcal/mol, while the heat of reaction between NaOH(aq) and HCl(aq) was found to be -54.6 kcal/mol. By combining these values, we predicted a heat of -101.8 kcal/mol and experimentally obtained -118.4 kcal/mol, which confirmed our hypothesis.
Introduction
The empirical determination of the change in enthalpy of a reaction is facilitated through the use of coffee cup calorimetry. Enthalpy, often expressed as Q + PV (where Q is the heat change, P is pressure, and V is volume), can be effectively measured as the change in temperature (Q = mcΔT), where m is the mass, c is the heat capacity, and ΔT is the change in temperature, given that pressure remains constant. By calculating the heat of dissociation in NaOH(s) to NaOH(aq) and the heat of the acid-base reaction between sodium hydroxide and hydrochloric acid, we can utilize Hess's Law to determine the heat of the reaction: NaOH(s) + HCl(aq) → H2O(l) + NaCl(aq).
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This study analytically calculates the heats of all three reactions, allowing us to hypothesize that the heats of the individual reactions can be summed to obtain the heat of the third reaction.
Methods and Materials
We employed coffee cups with a plate lid as our calorimeter, upon which the temperature probe was placed.
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Our initial step involved recording measurements, weights, and temperature changes. Subsequently, we dissolved NaOH pellets into room temperature water and monitored the temperature change. Temperature readings were taken every 0.5 seconds for 1 minute or until the temperature stabilized after pellet addition. Utilizing these temperature readings, we identified the critical temperature at which the exothermic reaction ceased providing sufficient heat to counteract cooling. The final experiment involved the reaction between NaOH(aq) and HCl(s). Due to the rapid nature of this reaction, we recorded temperatures every second. Waste solutions were disposed of in designated containers within the fume hood. The calorimeter and all reusable equipment were thoroughly rinsed and dried. Given the use of acids and bases, safety protocols were followed, including the availability of spill kits and proper disposal of NaOH(aq) waste.
- Coffee cup calorimeter
- Analytical balance
- Glass stirring rod
- Thermal probe
- 50 ml measuring cylinders
Results and Discussion
The experimental results revealed a decrease in the water temperature from 43.0°C to 39.1°C over 190 seconds. In contrast, the temperature of sodium hydroxide increased from 17.1°C at 10 seconds to 20.9°C at 280 seconds, while hydrochloric acid exhibited a significant temperature rise from 18.0°C to 29.3°C during the same time interval.
The experimental results are presented in the following table:
| Time (s) | Water Temperature (°C) | Sodium Hydroxide Temperature (°C) | Hydrochloric Acid Temperature (°C) |
|---|---|---|---|
| 0 | 43.0 | 17.1 | 18.0 |
| 190 | 39.1 | 20.9 | 29.3 |
To further analyze the data:
- Calculate the changes in enthalpy for all three reactions.
- Perform all calculations using the provided spreadsheet dedicated to the experiment.
The primary objective of this experiment was to verify Hess's law, which states that the sum of the enthalpy changes of two reactions is equal to the enthalpy change of a third reaction. Our results substantiate this principle by combining the enthalpy changes of the individual reactions.
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Hess’ Law Lab Explained & Answers
- Hess’ Law Lab Explained &…
Introduction
This lab is an experiment involving thermodynamics that aims to determine the enthalpy change of a chemical reaction through calorimetry. Enthalpy is a thermodynamic quantity that is related to the amount of heat released or absorbed during a chemical reaction. Hess’s law is based on the principle that the enthalpy change of a chemical reaction is independent of the pathway taken, and is only dependent on the initial and final states of the system. In this experiment, the objective is to determine the enthalpy change of a reaction by indirectly measuring the heat released or absorbed during the reaction using calorimetry. The enthalpy change of a reaction can be calculated using Hess’s law and the enthalpy changes of other reactions. This experiment involves finding the enthalpy of two reactions and utilizing one known enthalpy to determine the enthalpy change of a fourth unknown reaction. Calorimetry is a technique used to measure the heat of a chemical reaction by measuring the temperature change in a system. In this experiment, the temperature change is measured using a calorimeter, a device designed to insulate the system and measure the temperature change. The calorimeter used in this experiment is a coffee cup calorimeter, which consists of a styrofoam cup with a lid and a thermometer. The enthalpy change of a reaction can be calculated using the equation:
→ ΔH is the enthalpy change of the reaction,
→ q is the heat absorbed or released by the reaction
→ n is the amount of substance in moles.
Hess’s law can be used to calculate a reaction’s enthalpy change if other reactions’ enthalpy changes are known. Hess’s law states that the enthalpy change of a reaction is equal to the sum of the enthalpy changes of the reactions that make up the overall reaction, where each reaction is multiplied by a coefficient to balance the equation. Overall, the Hess’ law experiment is an important experiment in the field of thermodynamics, as it allows for the determination of the enthalpy change of a chemical reaction by measuring the temperature change in a system.
This information can be used to understand the energetics of chemical reactions better and to make predictions about the behavior of chemical systems.
The purpose of this investigation is to use Hess’s law to determine the molar enthalpy of combustion of magnesium, using calorimetry.
If the change in enthalpy is observed in the reaction of Mg and MgO with HCl, then the resulting reaction will be an exothermic reaction with an enthalpy change of -618.9 kJ
What is the molar enthalpy of combustion, ΔHC of magnesium?
- Eye protection
- Centigram or milligram balance
- Thermometer
- Polystyrene calorimeter
- 100-mL graduated cylinder
- 10- to 15-cm strip of magnesium ribbon
- Magnesium oxide powder
- 1.00 mol/L hydrochloric acid
Experimental Design
Measured masses of magnesium and magnesium oxide will be added to measured volumes of known concentration hydrochloric acid solution. The temperature changes will be determined. Calculated enthalpies of the reaction will be combined, using Hess’s law, to determine the enthalpy of combustion of magnesium.
- Measured 100.0 mL of 1.00 mol/L hydrochloric acid into a polystyrene cup
- Measured the initial temperature of the acid solution to the nearest 0.2°C
- Polished a length of magnesium ribbon with steel woolDetermined the mass (± 0.01g) of approximately 0.5 g of magnesium metal and added it to the solution containing 1.00 mol/L hydrochloric acid
- Stirred the solution and recorded the maximum temperature that the solution attains
- Disposed of the products as directed by the instructor, rinsed and dried the equipment
- Repeated steps 1 to 6 using approximately 1 g of magnesium oxide powder (± 0.01g)
Pre-Lab Question
* Show how the three known equations and their enthalpies of reaction can be combined, using Hess’s law, to yield the target equation and its enthalpy of combustion
* Therefore, the calculated ΔH of magnesium is -618.9 kJ
Observations
| Item | Temperature (°C) |
| 100 mL of 1.00 mol/L HCl (aq) | 21.9 |
| with ≈ 0.5 g of Mg (s) | 40.6 |
| 100 mL of 1.00 mol/L HCl (aq) | 24.5 |
| with ≈ 1 g of MgO (s) | 29.1 |
* Was the enthalpy changes exothermic or endothermic?
During the experiment, it was observed that both chemical reactions release heat into their surroundings, indicating they were exothermic reactions. The overall enthalpy change, which reflects the amount of heat absorbed or released during a reaction, showed a negative value, further confirming that the reactions were exothermic. When magnesium metal (Mg (s)) and magnesium oxide (MgO (s)) were added to the system, the temperature of the solution and the surrounding environment increased. This was due to the release of thermal energy by the exothermic reactions, which was absorbed by the surrounding solution. The release of this energy to the surroundings, in addition to the heat released by the reactions, is indicative of an exothermic change.
The energy absorbed by the surrounding solution was transferred from the system reaction.
The reaction’s change in enthalpy is:
* Which of the measured values limited the precision of your value?
In the process of conducting the experiment, it became clear that the majority of the values, including substance mass and volume, were under control, especially the mass of the hydrochloric acid, magnesium, and magnesium oxide, as well as the enthalpy change of the water and its specific heat capacity. Most of the numbers used in the calculations had nothing to do with the experimental procedures and depended on how long after the reaction had finished before the temperature was recorded. Temperature could change at any time due to its environment or the thermometer’s inherent inaccuracy. Furthermore, every time the calorimeter was opened, heat could escape, changing the reaction’s temperature. Thus, the one set of
measured values in this experiment that was responsible for errors in the final enthalpy value was the temperature.
* Explain how and why your calculated enthalpies of reaction would be inaccurate if…
i) Some heat were transferred to the air or Styrofoam cup;
If some heat were transferred to the air, the heat leaving the closed system would not be accounted for when measuring temperature. The continuous heat loss to the air would decrease temperature, making it difficult for experimenters to determine the accurate amount of energy required for the reaction to occur initially. The calculations for enthalpies would show lower temperature values as the HCl (aq) would absorb less heat, ultimately resulting in a lower overall value for the enthalpies of the reaction. During the experiment, the heat of solution was used to determine the heat of reaction, and if some heat was lost to the air, the enthalpies of the reactions would be less exothermic than the theoretical value.
ii) The surface of the magnesium ribbon had a coating of MgO;
If the magnesium ribbon had a coating of magnesium oxide (MgO (s)), it would be oxidized during the reaction with hydrochloric acid, and this would impact the overall enthalpy of the reaction. The reaction between MgO and HCl would result in oxygen reacting with the acid before the magnesium could, increasing the temperature of the solution. As the reaction lengthens, more energy would be released to the surroundings, resulting in a decrease in the final enthalpy of combustion of magnesium. In summary, the presence of a coating of MgO on the surface of a magnesium ribbon would decrease the enthalpy of the reaction, making it inaccurate to measure the actual enthalpy change. It is, therefore, essential to ensure that the magnesium ribbon used in the experiment is clean and free of any impurities that may impact the reaction.
Suggest some other possible sources of experimental error in this investigation. There are several sources of experimental error that could have affected the results of this investigation. One source of error is related to the equipment used in the experiment. For example, if the thermometer was not calibrated properly, it could have produced inaccurate temperature readings, leading to errors in the calculation of the enthalpy change. Additionally, if the calorimeter used to hold the HCl was not completely dry and contained some water, it would have introduced extra water into the system, leading to reactions which were unaccounted for.
Another source of error is related to the assumptions made during the experiment. The assumption that the specific heat capacity of the metal was constant may not have been accurate, as the specific heat capacity can vary with temperature and other factors. There may also have been errors introduced during the experiment’s data collection and analysis phases. For example, if the temperature readings were not taken at the same time intervals, it could have affected the accuracy of the calculated results.
Additionally, if the measurements were not recorded accurately, or if there were errors in the calculations performed to determine the enthalpy change, this could have led to inaccuracies in the final results. Finally, errors may have been introduced due to human error or bias. Errors such as misreading measurements or incorrectly recording data could have affected the accuracy of the calculated enthalpy change.
* The accepted value for the molar enthalpy of combustion of magnesium is -601.6 kJ/mol. Calculate a percentage difference by comparing your experimental values and the accepted values .
The percentage difference between the experimental value and the accepted value is 4.8 %
Is Hess’s law an acceptable method to calculate enthalpies of reaction?
During the lab experiment, a comparison was made between the theoretical and experimental values using Hess’s Law to calculate enthalpies of reaction. It was observed that the percentage difference between the theoretical and experimental values was approximately 4.8%, which is below the conservative acceptable percent difference of 5%. Other potential sources of error, such as heat loss through the calorimeter and other human errors, were also taken into account. After considering these factors, it can be concluded that Hess’s Law is an acceptable method to calculate enthalpies of reaction. The results obtained from the experiment demonstrate that Hess’s Law provides reliable values for enthalpies of reaction, indicating its usefulness in practical applications.
* Suggest an experimental technique that could be used to determine the enthalpy of magnesium combustion directly.
Bomb calorimetry is an experimental technique that is highly effective in determining the enthalpy of combustion of a substance, including magnesium. This method is based on the principle that when a substance is burned in an oxygen-rich environment, the heat generated during the combustion reaction can be used to calculate the enthalpy of combustion. The process of bomb calorimetry involves placing a sample of the substance inside a bomb, which is then filled with pure oxygen. The bomb is placed in a calorimeter containing water and the initial temperature of the water is recorded before the combustion reaction is initiated.
When the substance in the bomb is ignited, the heat released by the reaction is transferred to the surrounding water in the calorimeter, causing its temperature to rise. The temperature change is then monitored until it reaches a stable value, indicating that the reaction is complete. By measuring the mass of the substance burned and the temperature change of the water, it is possible to calculate the enthalpy of combustion of the substance using the formula q = m x c x ΔT, where q is the heat released, m is the mass of water, c is the specific heat capacity of water, and ΔT is the temperature change of water. Bomb calorimetry is a highly precise technique, providing accurate and reliable measurements, which could be used to determine the enthalpy of combustion of magnesium.
This lab aimed to determine the molar enthalpy change for the combustion of Mg through Hess’s Law. The final molar enthalpy change in the reaction was observed to be -631.21 kJ. This value was acquired using Hess’s law to determine the total enthalpy change through the reaction of Mg, HCl, MgO, and HCl. Using the enthalpy changes from these two reactions, we were able to calculate the total enthalpy change for the combustion of Mg.
This lab proved useful in demonstrating the use of a calorimeter and Hess’s Law to determine the change in enthalpy of a reaction. The lab also allowed us to observe the change in temperature and energy produced due to an exothermic reaction and how different types of reactions can have an impact on the energy produced. A few things that could be improved in a future experiment could be to ensure that no energy is lost to the surroundings which could have had an effect on the temperature readings. In conclusion, this lab successfully demonstrated calculating the enthalpy change of a reaction using Hess’s Law.
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lab report on Hess's Law thermodynamics and calorimetry objective: the purpose of the lab is to combine two reactants in the calorimeter and measure the heats. ... Another important aspect of this experiment is that an object's or solution's temperature will rise in proportion to how much heat it has absorbed. The increase in temp that is ...
Experiment 009: Hess' Law References: Suzanne Slayden, 2018, Chemistry 213, 214, 272 Laboratory Experiments, 7th Edition, pages 79-92. George Mason University, Department of Chemistry and Biochemistry. ... Hess' Law - This is a lab report for Chem-213 at George Mason University. Course: General Chemistry Lab II (Chem 213) 78 Documents.
2) This experiment taught us how to use Hess's law to calculate the energy change in a reaction through experimentation. We learned how to use the sum of the individual reactions in our reaction to calculate it's change in energy with experimental data. 3) In this lab we also learned how to convert and alternate units.
The heat of formation, f, which we will determine today is simply the change in enthalpy for the reaction (1) below: (1) Mg(s) + 1⁄2 O2(g) MgO(s) f (1) Note that the reaction is written for formation of one mole of MgO(s), which requires the use of. a fractional coefficient for O2, and that all physical states must be specified, since ...
For example, in this experiment you will examine an acid-base neutralization in aqueous solution: H3O+(aq) + OH-(aq) → 2 H2O(l) ∆H = -55.8kJ (9-2) The enthalpy change for this reaction could be given in J/(mol of H3O+), or in J/(mol of OH−), or in J/(mol of H2O). To avoid confusion it is customary to report H for the reaction with the ...
Chemistry 212 Lab 9 Calorimetry and Hess's Law 5 6. The file, "Experiment 9 - Calorimetry and Hess's Law" will launch the "Logger Pro" program. The program will display a data table and a graph, Figure 9.3. Notice the time axis scale is 0-180 seconds. This is the default collection time for this experiment and data
reactions. From this information and your knowledge of Hess's law, you will calculate the heat of reaction for magnesium burning in the air. Pre-Lab Questions: 1. In your own words, state the basis of Hess's law 2. Write the balanced chemical equations for the three reactions described in the Introduction. 3.
Report Questions When necessary, answer the report questions on a separate piece of paper (only a few reports have these in the lab manual). Include the sheet torn out of the lab manual and number your questions. Always support your answers with calculations and/or explanations. A simple numerical answer without any
Hess's Law states that if a series of reactions can be added together to make a certain overall reaction, then their enthalpies can also be added together in the same manner to find the enthalpy for the reaction of interest. For this experiment, the reactions used are shown in Eqn. 2-4: Mg(s) + 2 HCl(aq) ® MgCl2(aq) + H2(g) DH2° Eqn. 2.
LAB 2 (Week 3) The Density of Liquids and Solids; LAB 3 (Week 4) Nomenclature of Ionic Compounds; LAB 4 (Week 5) Chemical Formlua Determination; LAB 5 (Week 6) Types of Reactions; LAB 6 (Week 7) Mole Ratios and Reaction Stoichiometry; LAB 7 (Weeks 8 & 9) Titration of Vinegar; LAB 8 (Week 10) Calorimetry and Hess's Law. Learning Outcomes ...
Hess's Law Lab Report Completed by -- Partners: -- On October 24th, 2019. Abstract: This lab was conducted to determine the enthalpy for the combustion of magnesium metal using Hess's Law. The temperature of Hydrochloric acid was taken, and then taken once again after reacting with magnesium. The same was done for magnesium oxide, and this ...
In this experiment, you will use a Styrofoam-cup calorimeter to measure the heat released by three reactions. One of the reactions is the same as the combination of the other two reactions. Therefore, according to Hess's law, the heat of reaction of the one reaction should be equal to the sum of the heats of reaction for the other two. This concept is sometimes referred to as the additivity ...
In this experiment, we aimed to validate Hess's Law by calculating the heat of reaction using coffee cup calorimeters. We investigated the reactions involving NaOH, aqueous NaOH, and hydrochloric acid. The heat generated during the dissociation of NaOH was determined to be -47.2 kcal/mol, while the heat of reaction between NaOH (aq) and HCl (aq ...
Introduction This lab is an experiment involving thermodynamics that aims to determine the enthalpy change of a chemical reaction through calorimetry. Enthalpy is a thermodynamic quantity that is related to the amount of heat released or absorbed during a chemical reaction. Hess's law is based on the principle that the enthalpy change of a chemical
It is published by Germain Hess in 1840. Hess law can be used to calculate the undetermined of ΔH. On the other hand Hess law can be used to express the law of the conservation energy which tells the energy neither can be created nor destroyed. These are the application of Hess Law : Calculate heat change of heat phase transition.
carefully. If you need to repeat the experiment, you still must be done with the write up and post-lab questions before the end of the lab period. 9. Rinse and fill a cuvette with your assigned unknown. Place the cuvette in the spectrometer. Record the absorbance in your lab report once the reading has stabilized. 10.
CHM 271 Datasheet Experiment 4; LAB Report BIO320 Practical 4 EXP 1 ( Plantae) Script for CHM301 - PRESENTATION; Universiti Teknologi MARA; Related documents. ... (EXPERIMENT 1: HESS LAW) PREPARED BY: STUDENT NUMBER: GROUP: A4AS1202_ DATE OF EXPERIMENT: 10 MARCH 2020 DATE OF SUBMISSION: 20 MAY 2020 INSTRUCTOR:
View Lab - Enthalpy of Neutralization Lab Report.docx from CH 152 at CUNY Queensborough Community College. QUEENSBOROUGH COMMUNITY COLLEGE CHEMISTRY DEPARTMENT CH151L/152L GENERAL CHEMISTRY LAB 1. ... When the bonds were broken and new bonds were formed , energy was released . This experiment serves to verify the atomic theory and the ...
Please note that while heating by an electrical current, the heat flux q is a given value and surface temperature T w that is an unknown value, i.e. T w (q)is the function, while in Richmann's experiments the function is q(T w). Fig. 2 presents experimentally obtained dependence of wall temperature on the density of a heat flow. Axis of ordinates show wall temperature T w, axis of abscissas ...
part of lab report sample calculations: all calculations are the same for part and part with the exception of the last few calculations mass of the hcl solution ... The anticipated outcome is the results were help determine the accuracy of Hess' law in the experiment where the sum of reactions was equal to the heat of reaction produced by one ...
Avoid this form using the first person: "From this experiment I learned that solution A was more concentrated than Solution B." Abstract. Content. The title of your report makes only the simplest statement about the content of the report. The abstract gives a general overview summarizing the purpose, methods, major findings and conclusions.