lecture 3

lecture 3 - CHEM 6BL Experiment 3: Thermochemistry...

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CHEM 6BL Experiment 3: Thermochemistry Instructor: Dr. S. Berniolles Page 1 1 Chemistry 6BL Lab/Course Schedule Chemistry 6BL Lab/Course Schedule --- Expt. 1 Report Expt. 2 (Parts III-IV) Expt. 2 (Part V) 1 st lab 2 nd lab Thermochemistry (Expt. 3) Oct. 13 Prelab & Report Due Dates Lab Schedule Lab Period Lecture & Exam Schedule Date 2 Experiment 3: Thermochemistry Experiment 3: Thermochemistry The study of the relationships between heat energy and chemical changes z Heat energy RELEASED by a reaction: EXOTHERMIC z Heat energy ABSORBED by a reaction: ENDOTHERMIC 3 Heat Transfer Heat Transfer System or Object Endo Endo (into) Exo Exo (out of)
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CHEM 6BL Experiment 3: Thermochemistry Instructor: Dr. S. Berniolles Page 2 4 Heat Transfer Between Systems Heat Transfer Between Systems Energy/Heat will transfer between two systems brought into contact z Systems in contact will “ equilibrate z Result is a change in temperature (i.e., heat flow ) 5 Heat Flow Heat Flow Heat flow takes place between system (or object) and (usually) the surroundings z System/Object : water, ice, metal, reaction, etc. z Surroundings : liquid/solvent, beaker/container, atmosphere (ambient) z Heat Flow Heat gained from surroundings = +ve ( T = +) Heat lost to surroundings (cooled) = -ve ( T= -) 6 Heat Capacity Heat Capacity The amount of heat energy required to raise the temperature of a substance by 1 K (1°C) Two types of Heat Capacity: z Specific Heat Capacity (c):J/K x g z Molar Heat Capacity (C):J/K x mol
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CHEM 6BL Experiment 3: Thermochemistry Instructor: Dr. S. Berniolles Page 3 7 Molar Heat Capacity z At constant pressure : C p z At constant volume : C v z Experiment #3 done under constant P z Heat capacity relates to heat change via: q p = nC p T or q = mc T 8 Heat Capacities of Substances Heat Capacities of Substances z Heat Capacity of water is large : C P = 75.3 J/K·mol c = 4.18 J/K·g C p = c × M (where M = 18 g/mol) z Molar Heat Capacities of (transition) metals are about equal: C P 26 J/K·mol Known as the Law of Dulong and Petit Relates to the very similar atomic structure of such metals 9 Total Heat Change Total Heat Change z Total Heat Change (during a reaction): q p = nC p T (or q = mc T) z Total Heat is equal to Enthalpy (at constant pressure) q p = H z Enthalpy can be positive or negative
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CHEM 6BL Experiment 3: Thermochemistry Instructor: Dr. S. Berniolles Page 4 10 Enthalpy Enthalpy z
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lecture 3 - CHEM 6BL Experiment 3: Thermochemistry...

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