Thermochemistry — Measuring Heat in Chemical Reactions
10 experiments
Thermochemistry experiments quantify the heat absorbed or released during chemical and physical processes. Using calorimeters ranging from simple coffee-cup designs to sophisticated bomb calorimeters, students measure enthalpy changes and verify Hess's law — that enthalpy change depends only on initial and final states, not the reaction pathway.
Learning Objectives
Determine enthalpy of neutralization, dissolution, and combustion experimentally. Verify Hess's law using multi-step reactions. Calculate specific heat capacities. Understand the difference between system and surroundings, exothermic and endothermic processes, and calorimeter calibration.
Key Techniques
Coffee-cup calorimetry: mix reactants in an insulated container, measure temperature change, and calculate q = mcDeltaT. Bomb calorimetry: combust samples in a sealed oxygen-filled vessel and measure the water temperature rise. Calibrate calorimeters with a known reaction (e.g., benzoic acid combustion). Plot temperature vs. time to extrapolate the maximum temperature change.
Equipment Overview
Required: nested polystyrene cups (coffee-cup calorimeter), thermometer or temperature probe, magnetic stirrer, graduated cylinder, analytical balance. Advanced: bomb calorimeter, oxygen cylinder, ignition wire, Parr press for pellet formation.
Bomb Calorimetry Simulation
Measuring the energy content of food using calorimetry
Measure the energy (calorie) content of different food items by burning them and measuring the heat transferred to water.
Coffee Cup Calorimetry
Measuring enthalpy of neutralization using a simple calorimeter
Determine the enthalpy of neutralization of HCl and NaOH using a polystyrene cup calorimeter.
Cold Pack Chemistry
Studying the endothermic dissolution of ammonium nitrate
Measure the temperature change when ammonium nitrate dissolves in water, demonstrating an endothermic dissolution process used in instant cold packs.
Dissolving Is Not Always Exothermic
Comparing temperature changes of different salt dissolutions
Compare the enthalpy of dissolution of different salts (NaOH, CaCl₂, NH₄NO₃, KNO₃) to show that dissolution can be exothermic or …
Endothermic Reaction Demonstration
Barium hydroxide and ammonium thiocyanate cold reaction
Demonstrate a dramatically endothermic reaction where the mixture becomes cold enough to freeze water on the outside of the flask.
Enthalpy of Fusion of Ice
Measuring the energy required to melt ice
Determine the enthalpy of fusion of ice by adding a known mass of ice to warm water and measuring the …
Exothermic Crystallization of Sodium Acetate
Measuring the heat released during instant crystallization
Quantify the heat released during the crystallization of supersaturated sodium acetate using calorimetry.
Heat of Combustion of Magnesium
Determining ΔH using Hess's law and magnesium oxide
Determine the enthalpy of combustion of magnesium indirectly using Hess's law, since direct measurement is impractical.
Hess's Law Verification
Confirming that enthalpy is a state function using three reactions
Verify Hess's law by measuring the enthalpy changes of three related reactions and showing that ΔH1 + ΔH2 = ΔH3.
Specific Heat Capacity of Metals
Comparing heat capacities of aluminum, copper, and iron
Determine the specific heat capacity of several metals using the method of mixtures and compare with accepted values.