### Transcription for Educational Website #### Instructions 7. **Calculate the number of moles of NaOH used in the reaction** by multiplying the volume of NaOH times the molarity (1.000 mol/L). Record the results in the results table. 8. **Calculate ΔHrxn, in kJ/mol, of NaOH for the reaction** and record the results in the results table. Make sure the sign of ΔHrxn is correct. #### Results Table | Mass of Rxn Mixture | ΔT | Total Heat Released | mol NaOH | ΔHrxn/mol | |---------------------|----|---------------------|----------|----------------------| This table is designed to help record data from the experiment, including the mass of the reaction mixture, change in temperature (ΔT), total heat released, moles of NaOH, and the enthalpy change per mole (ΔHrxn/mol). **3-10: Heat of Reaction: NaOH(aq) + HCl(aq)** Energy is either absorbed or released for all chemical reactions, and we call this energy the enthalpy of reaction (ΔHrxn). If the enthalpy of reaction is positive, then we say that the energy was absorbed or that the reaction was *endothermic*. If the enthalpy of reaction is negative, then we say that energy was released or the reaction was *exothermic*. Most chemical reactions are exothermic. In this problem, you will measure the amount of heat released when aqueous solutions of NaOH and HCl are mixed and react to form water and then you will calculate the heat of reaction. \[ \text{NaOH(aq) + HCl(aq)} \rightarrow \text{H}_2\text{O(l) + NaCl(aq)} \] 1. **Start Virtual ChemLab**, select **Thermodynamics**, and then select **Heat of Reaction: NaOH(aq) + HCl(aq)** from the list of assignments. The lab will open in the Calorimetry laboratory. 2. In the thermometer window click **Save** to begin recording data. Allow 20-30 seconds to obtain a baseline temperature of the water. Pour the left beaker containing 100 mL of 1.00 M HCl into the calorimeter and then pour the right beaker containing 100 mL of 1.00 M NaOH into the calorimeter. Observe the change in temperature until it reaches a maximum and then record data for an additional 20-30 seconds. Click **Stop** in the temperature window. (You can click on the clock on the wall labeled **Accelerate** to accelerate the time in the laboratory.) A data link icon will appear in the lab book. Click on the data link icon and record the temperature before adding the NaOH and the highest temperature after adding the NaOH in the data table. (Remember that the water will begin to cool down after reaching the equilibrium temperature.) **Data Table** | NaOH/HCl | | |-------------------|---------------| | Initial temperature (°C) | 25.0°C | | Final temperature (°C) | 31.5°C | 3. **Is the observed reaction endothermic or exothermic? What will be the sign