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Chapter 6

CHEM 1050 Chapter Notes - Chapter 6: Enthalpy, Endothermic Process, Exothermic Process


Department
Chemistry
Course Code
CHEM 1050
Professor
Lori Jones
Chapter
6

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Week 1
Thermochemistry
Week 1
6.1 Energy and its Units
Energy: the potential or capacity to move matter
o A property of matter and exists in different forms that can be converted
Kinetic Energy: the energy associated with an object by virtue of its motion o EK = ½mv2 Ek is kinetic
energy; m is mass; v is speed/velocity
o Shows that kinetic energy depends on mass and the speed at which an object is travelling
Heavy object moves slower than light object
Joule: the SI unit of energy (kg·m2/s2)
Calorie (cal): a non-SI unit of energy commonly used by chemists, originally defined as he amount of
energy needed to raise the temperature of 1 gram of water by 1 degree
Celsius o Later defined as: 1 cal = 4.184 J
Potential Energy: the energy an object has by virtue of its position in a field of force
Internal Energy (U): the sum of the kinetic and potential energies of the particles making up a
substance
o Etot = EK + EP + U
Usually substance is studied in a vessel so the kinetic energy is 0. Also potential energy as
a whole is a constant and is taken as 0, so in these cases, total energy = internal energy
Law of Conservation of Energy: energy may be converted from one form to another, but the total
quantity of energy remains constant
6.2 First Law of Thermodynamics: Work and Heat
Thermodynamic system (or system): the substance or mixture of substances under study in which a
change occurs
Surroundings: everything in the vicinity of the thermodynamic system
Work: the energy exchange that results when a force (F) moves an object through a distance (d); work
(w) equals F × d
Heat: the energy that flows into or out of a system because of a difference in temperature between
the thermodynamic system and its surroundings o As long as a system and its surroundings are in
thermal contact, energy (heat) flows between them to establish temperature equality or thermal
equilibrium
o Heat flows from higher temperature to lower temperature and once the temperatures become
equal, heat flow stops added heat in a system appears as an increase in its internal energy
o Heat is only an energy flow a syste does ot ha e heat
If the surroundings decrease in energy, it means that the system absorbed energy so you would write q
= +x J, with x being the amount of energy
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