Hess Law
Heats of Reaction – Hess’s Law
Overview
Hess’s Law states that the energy change for a reaction depends on the enthalpy of the reactants and products and is independent of the pathway of the reaction. In this experiment you will use calorimetry to measure the heats of reaction for three reactions: Reaction 1 Reaction Equation NaOH(s) → Na+(aq) + OH-(aq) Solid NaOH is dissolved in water 2 Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) Solutions of NaOH and HCl are mixed 3 NaOH(s) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) Solid NaOH is dissolved in a HCl solution The third reaction is actually a combination of the first two reactions. Notice that the equation for Reaction 3 can be obtained by adding together reactions 1 & 2. By calculating the heats of reaction for all three reactions you will be attempt to verify Hess’s Law: ΔH3 = ΔH1 + ΔH2 ΔH3 ΔH2 You will determine: ΔH1
Purpose •
To measure experimentally the amount of heat absorbed or released during the dissolving of ammonium nitrate and of sodium acetate in water.
2.0 g of solid NaOH is dissolved in 100 mL of water. The initial and final temperatures are measured and recorded. The heat of solution is calculated (ΔH1) Reaction 2. Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) 50 mL of 1.0 M hydrochloric acid solution is combined with 50 mL of 1.0 M sodium hydroxide solution. The initial and final temperatures are recorded, and the heat of the reaction is calculated (ΔH2) Reaction 3. NaOH(s) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) 2.0 g of solid NaOH is dissolved in 200 mL of 0.50 M HCl. The heat of reaction is calculated (ΔH3)
Equipment, Materials, and Procedure
Your teacher will provide you with a list of the materials and equipment required for this lab, and the procedures to follow. SAFETY PRECAUTIONS MUST BE STRICTLY FOLLOWED! If you are unable to actually perform the experiment, use the following set of experimental data to plot the graphs and
Overview
Hess’s Law states that the energy change for a reaction depends on the enthalpy of the reactants and products and is independent of the pathway of the reaction. In this experiment you will use calorimetry to measure the heats of reaction for three reactions: Reaction 1 Reaction Equation NaOH(s) → Na+(aq) + OH-(aq) Solid NaOH is dissolved in water 2 Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) Solutions of NaOH and HCl are mixed 3 NaOH(s) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) Solid NaOH is dissolved in a HCl solution The third reaction is actually a combination of the first two reactions. Notice that the equation for Reaction 3 can be obtained by adding together reactions 1 & 2. By calculating the heats of reaction for all three reactions you will be attempt to verify Hess’s Law: ΔH3 = ΔH1 + ΔH2 ΔH3 ΔH2 You will determine: ΔH1
Purpose •
To measure experimentally the amount of heat absorbed or released during the dissolving of ammonium nitrate and of sodium acetate in water.
2.0 g of solid NaOH is dissolved in 100 mL of water. The initial and final temperatures are measured and recorded. The heat of solution is calculated (ΔH1) Reaction 2. Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) 50 mL of 1.0 M hydrochloric acid solution is combined with 50 mL of 1.0 M sodium hydroxide solution. The initial and final temperatures are recorded, and the heat of the reaction is calculated (ΔH2) Reaction 3. NaOH(s) + H+(aq) + Cl-(aq) → Na+(aq) + Cl-(aq) + H2O(l) 2.0 g of solid NaOH is dissolved in 200 mL of 0.50 M HCl. The heat of reaction is calculated (ΔH3)
Equipment, Materials, and Procedure
Your teacher will provide you with a list of the materials and equipment required for this lab, and the procedures to follow. SAFETY PRECAUTIONS MUST BE STRICTLY FOLLOWED! If you are unable to actually perform the experiment, use the following set of experimental data to plot the graphs and