Energy Unit 7 Enthalpy PE diagrams Phase Changes

Energy Unit #7: Enthalpy, PE diagrams, Phase Changes, IMF, BP Curves, Specific heat, Latent heat, Heating/cooling curves

Change in Enthalpy The change in enthalpy-the enthalpy of the products minus the enthalpy of the reactants 2

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Entropy – Law of Disorder Entropy (S) – a measure of the disorder or randomness of the particles that make up a system Law of Disorder – Spontaneous processes ALWAYS proceed in a way that the entropy of the universe increases (increase disorder) 5

Entropy (cont. ) Entropy changes associated with state of matter: Solids – molecules are tightly packed and cannot move (more order) Liquids – molecules have some freedom to move (some order) Gas – unrestricted movements (very little order) Entropy increases as a substance changes from solid liquid gas 6

Phase Diagrams Is a graphic that shows effects of pressure & temperature on a substance • Melting/Freezing: any point on curve line- both solid & liquid • Sublimation/deposition : any point on curve-both solid & gas • Vaporization/condensation : any point on curve-both liquid & gas • Vapor pressure ends at Critical point 7

Phase diagrams (cont. ) Critical Point- the temperature above which the gas CANNOT be liquefied Critical point is called a supercritical fluid- not distinguishable between gas/liquid 8

Triple Point Condition of temperature & pressure where all 3 phases exist in equilibrium Phase Diagram for water is different! 9

Specific Heat Capacity Cp or s Definition-amount of heat required to raise the temperature of 1 gram of a substance by 10 C Remember: Q=m●c●ΔT Mass of substance (g or Kg) Specific heat capacity (J/g ● 0 C) ΔT- change in temperature (final – initial) Energy (J) 10

Cp of Common Materials 11