Basic Thermochemistry

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Slide 1

Basic Thermochemistry

Courtesy of lab-initio.com

Slide 2

CA Standards

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Units for Measuring Heat

The Joule is the SI system unit for measuring heat:

The calorie is the heat required to raise the temperature of 1 gram of water by 1 Celsius degree

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Heat (Enthalpy) Change, ΔH

Definition: The amount of heat energy released or absorbed during a process.

Energy

Energy is the capacity to do work, and can take many forms

Potential energy is stored energy or the energy of position

Kinetic energy is the energy of motion

Thermal energy (heat) is an outward manifestation of movement at the atomic level

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Calorimetry

The amount of heat absorbed or released during a physical or chemical change can be measured, usually by the change in temperature of a known quantity of water in a calorimeter.

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Exothermic Processes

Reactants  Products + energy

Processes in which energy is released as it proceeds, and surroundings become warmer

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Endothermic Processes

Reactants + energy  Products

Processes in which energy is absorbed as it proceeds, and surroundings become colder

Slide 8

Water phase changes

Temperature remains during a phase change.

constant

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Phase Change Diagram

Processes occur by addition of energy 

 Processes occur by removal of energy

Slide 10

Phase Diagram

Represents phases as a function of temperature and pressure.

Critical temperature: temperature above which the vapor can not be liquefied.

Critical pressure: pressure required to liquefy AT the critical temperature.

Critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).