CH 204- Intro to Chem Practice Experiment 3-Enthalpy of Chemical Reaction Dana Lucas Robin Brown TA: Chris February 19, 2018 Introduction The purpose of this experiment was to calculate the change in enthalpy of 2 reactions using Hess’ Law by using a coffee calorimeter to measure the temperature changes in the sub reactions for MgO and a neutralization reaction. Germain Hess published this law in 1840, which described the first law of thermodynamics. In Hess’ Law, “the enthalpy change in a chemical reaction is independent of any intermediate reactions; that is, it is the same whether it takes place in one or several stages”1. The change in enthalpy can be described by the equation: The enthalpy, or heat, of reaction is described as products
2. Mix a combination of the NaClO and the thiosulfate solution equal to 50 ml in a Styrofoam cup, stir with thermometer, and record temperature in the data table. Dispose of solutions and rinse cup well. Continue taking data until you have enough data to record and make a thorough graph. 3.
Calculations steps: 1. We must now use the pV = nRT formula in order to get the molar mass (n) of SO2. For this we require all of the other variables which we got from the experiment which are the temperature, pressure and volume, but we also know the R constant which equals 8.314 J/kmol. 2. We can now rearrange the equation in order to make it easier to calculate only n. 3.
2H3C6H5O7(s) + 3Mg(OH)2 (s) → Mg3(C6H5O7)2 (aq) + 6H2O (l) In order to get to this end point, we used Hess’ Law which says that the enthalpy of a net chemical reaction is the sum of the enthalpy changes of each individual step. There were four steps, or reactions, where we measured the change in enthalpy. Step 1: Mg(OH)2(s) Mg(OH)2(slurry) Step 2:2H3C6H5O7(s) +Mg(OH)2(slurry)Mg3(C6H5O7)2 (aq) + 6H2O (l) Step 3:H3C6H5O7(s)H3C6H5O7(aq) Step 4:2H3C6H5O7(aq) + 3Mg(OH)2 (slurry) → Mg3(C6H5O7)2 (aq) + 6H2O (l) By determining the change in enthalpies for each step, we were able to add all of the individual enthalpies together to get the change in enthalpy for our goal reaction. The results can be seen in Figure 1. We were able to calculate qsol, qrxn, and ΔH using: qsol=mcT qsol+qrxn=0 Hrxn=qrxnmol
One possibility is to measure the change in mass of NaHCO3 by putting it on a weighing scale connected to the computer. As the is being produced the chemical will weigh less over time. However, a problem with this method is that it is hard to heat the compound when it is stationary on a balance. To solve that problem, I could have mixed sodium bicarbonate with an acidic compound, since that would produce carbon dioxide as well. However, I wanted to just focus on just baking soda, so another method needs to be used.
Part 2 - Preparation of NaCl solutions: Prepare 600 mL of each solution according to its concentration. Assuming that the density of each solution is approximately 1 g/mL, the mass of each solution will be 600 grams. (mass of solution=volume of solutiondensity of solution) In order to calculate the sodium chloride mass required for each solution use the following formula: mass of solution=mass of NaCl 100concentration of solution. For the solution of NaCl 5% are need 30 g NaCl and 570 mL water; for the solution of NaCl 8% are needed 48 g NaCl and 552 mL water; for the solution of NaCl 10% are needed 60 g NaCl and 540 mL water and for the solution of NaCl 15% are needed 90g NaCl and 510 mL water. Part 3 - Putting the NaCl solutions over the shell-less eggs: Place each shell-less egg into a new plastic cup.
Similarly, such factors would decrease the frequency of collisions amongst particles which will then decrease the rate of reaction. This information is obtained by analysing the chemical kinetics of a reaction which depend on various factors: reactant concentrations, temperature, physical states and surface areas of reactants, and
This proves that my hypothesis was correct. Furthermore, my data compared to other resources are fairly similar. The rate of reaction approximately doubles every time the temperature increases by the 10°C (Ingram, Paul). Whereas my rate of reactions double every 20°C instead of 10°C. This tells me that I was not accurate enough with my timing and measuring.
Analysis and Calculations The experiment is a strong acid-strong base titration. From this experiment, we can analyze concentration of base when the concentration of acid is known. The HCl solution, added with a few drops of phenolphthalein, is placed into the Erlenmeyer flask and the NaOH solution is slowly added from the burette into the HCl solution in small drops. Neutralization occurred in the titration process: NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l) This reaction shows that 1 mol of NaOH will react with 1 mol of HCl to produce 1 mol of the salt (NaCl) and 1 mol of water. Phenolphthalein indicator is used to determine the end-point of the titrated solution.