Molar Enthalpy Review Notes PDF

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Summary

These are high school review notes on the topic of molar enthalpy....

Description

Heat Transfer and Enthalpy Change ●

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Enthalpy(H): the total internal energy of a substance at constant pressure ○ The sum of many different forms of energy, both kinetic and potential present in a chemical system When applied to atoms and molecules, this includes ○ Moving electrons within atoms ○ The vibration of atoms connected by chemical bonds ○ The rotation and translation of molecules that are made up of these atoms ○ The nuclear potential energy of protons and neutrons in atomic nuclei ○ The potential energy of each atom within the molecule if it were to form more stable bonds

Enthalpy ● ● ●

Enthalpy change (ΔH): the energy absorbed or released to the surroundings when a system changes from reactants to products Enthalpy changes result from chemical bonds being broken or formed. RECALL: the formation of a bond releases energy, and breaking a bond requires energy 2 types of ΔH ○ Endothermic change: net absorption of energy by the chemical system. For an endothermic change, the temperature of the surroundings decreases ΔH is positive ○ Exothermic change: net release of energy by the chemical system. For an exothermic change the temperature of surroundings increases ΔH is negative

Enthalpy and Heat ●

As long as pressure remains constant, the enthalpy change of the chemical system is equal to the amount of heat transferred from or to the surroundings

Molar Enthalpy ●

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Molar enthalpy (ΔHx): the enthalpy change associated with a physical, chemical, or nuclear change involving one mole of a substance. The variable x indicates the type of change that is occuring ΔHx = ΔH/n = +-q/n ○ Where n is the number of moles of the substance (mol)

Representing Molar Enthalpy Changes ●

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Exothermic reactions ○ ΔHx is negative (loss of energy) ○ Energy is produced with products, so enthalpy change will be on the product side of the equation for exothermic reactions Endothermic reactions ○ ΔHx is positive (gains energy) ○ Energy is consumed by reactants, os enthalpy change will be on the reactant

side of the equation for endothermic reactions

Measuring Energy Changes: Calorimetry ● ● ●

Calorimetry is defined as the technological process of measuring energy changes in a chemical system A calorimeter is a device that is used to measure temperature changes in a chemical system, allowing us to calculate the amount of thermal energy absorbed/released The goal of a calorimeter is to make sure that all of the heat released/absorbed by a system is captured by the surrounding water. In reality, some will always be lost to the external surroundings (the insulation, etc.)

Using Calorimetry to Find Molar Enthalpies ● ● ●

No heat is transferred between the calorimeter and the outside environment Any heat absorbed or released by the calorimeter materials, such as the container, is negligible A dilute aqueous solution is assumed to have a density and specific heat capacity equal to that of pure water...