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CHEM161 Experiment 7: Calorimetry
Introduction
Calorimetry is the science of measuring heat flow, and heat is defined as thermal energy flowing from an object at a higher temperature to one at a lower temperature. For example, if a chunk of metal at room temperature is placed in a beaker of boiling water, the metal will absorb heat from the water until it is at the same temperature as the boiling water. Scientists also often study the heat associated with different physical and chemical changes. Ideally, the heat changes resulting from physical and chemical phenomena can be harnessed to do work. For example, the burning of gasoline and fossil fuels can be used to run our automobiles and heat our houses. However, in some cases, the heat associated with some processes is transferred to the environment; for example, traditional incandescent light bulbs use almost as much (or maybe more) electricity to produce heat rather than light. Most physical and chemical changes are either exothermic or endothermic. Exothermic reactions release energy or heat to increase the temperature of the surroundings; thus, the surroundings are hotter after an exothermic change. For example, nitroglycerine exploding is an extremely exothermic reaction. Endothermic reactions absorb energy or heat to decrease the temperature of the surroundings; thus, the surroundings are colder after an endothermic change. For example, cold packs used to relieve swelling joints or muscles often use chemicals that absorb heat when mixed, so the packs feel cold. When a reaction is carried out under constant pressure, the heat of a reaction is defined as the enthalpy change for the reaction (ΔH). Since most reactions occur under constant atmospheric pressure, the heat of a reaction is equal to ΔH, which is generally reported in units of kilojoules (kJ) per mole of the reactants and products as shown in the balanced thermochemical equation. For example, the reaction between hydrogen gas and oxygen gas to
Introduction
Calorimetry is the science of measuring heat flow, and heat is defined as thermal energy flowing from an object at a higher temperature to one at a lower temperature. For example, if a chunk of metal at room temperature is placed in a beaker of boiling water, the metal will absorb heat from the water until it is at the same temperature as the boiling water. Scientists also often study the heat associated with different physical and chemical changes. Ideally, the heat changes resulting from physical and chemical phenomena can be harnessed to do work. For example, the burning of gasoline and fossil fuels can be used to run our automobiles and heat our houses. However, in some cases, the heat associated with some processes is transferred to the environment; for example, traditional incandescent light bulbs use almost as much (or maybe more) electricity to produce heat rather than light. Most physical and chemical changes are either exothermic or endothermic. Exothermic reactions release energy or heat to increase the temperature of the surroundings; thus, the surroundings are hotter after an exothermic change. For example, nitroglycerine exploding is an extremely exothermic reaction. Endothermic reactions absorb energy or heat to decrease the temperature of the surroundings; thus, the surroundings are colder after an endothermic change. For example, cold packs used to relieve swelling joints or muscles often use chemicals that absorb heat when mixed, so the packs feel cold. When a reaction is carried out under constant pressure, the heat of a reaction is defined as the enthalpy change for the reaction (ΔH). Since most reactions occur under constant atmospheric pressure, the heat of a reaction is equal to ΔH, which is generally reported in units of kilojoules (kJ) per mole of the reactants and products as shown in the balanced thermochemical equation. For example, the reaction between hydrogen gas and oxygen gas to