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Chapter 7

CHEM 112 Chapter Notes - Chapter 7: Calorimeter, Thermal Energy, Intermolecular Force


Department
Chemistry
Course Code
CHEM 112
Professor
John Carran
Chapter
7

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Thermochemistry
-system: part of the universe chosen for study ex ocean, beaker
-surroundings: part of the universe outside the system with which the system interacts
-open system: freely exchanges energy and matter with the surroundings
-closed system: can exchange energy but not matter
-isolated system does not interact with its surroundings
-energy: capacity to do work
-work: force with distance
-kinetic energy: energy of a moving object
-potential energy: energy resulting from condition, position or composition, associated with attraction
and repulsion
-Thermal energy: kinetic energy associated with random molecular motion, generally proportional to
temperature
-also depends on the number of particles present ex. Small number of particles at a high temp
can have less thermal energy than a large number of particles at a lower temp
-Heat (q): transfer of thermal energy between a system and its surroundings as a result of temperature
difference
-can also cause a change in matter
-isothermal: process occurring at a constant temperature
-internal energy: energy content of a system
-heat is a form which energy is transferred
-the amount of heat required to change the temperature depends on the quantity, how much temp
needs to be changed and the nature of the substance
-Calorie: heat that’s required to change the temp of 1g of water by 1 degree Celsius
-heat capacity: quantity of heat required to change the temp of a system by 1 degree
-if the system is only 1 king of substance, it has a specific heat capacity
Quantity of heat=mass of substance x specific heat x temperature change or
Q= m x specific heat x ∆T *specific heat x mass= heat capacity (C)
Q=C x ∆
-When the temperature of a system increases, T is positive
-A positive Q value means that heat is absorbed/gained by the system
-law of conservation energy: total energy is constant: Qsystem + Qsurroundings = 0
-Chemical energy: associated with chemical bonds and intermolecular attractions
-heat of reaction (qrxn): quantity of heat exchanged between a system at constant temperature
-heat of combustion: heat released by a combustion reaction
-exothermic reaction: produced a temperature increase in an isolated system, gives off heat (negative q)
-endothermic is opposite
-calorimeter can help determine quantities of heat
-bomb calorimeter: suited for measuring the heat evolved in a combustion reaction
-everything in the calorimeter is isolated and considered a system
-qrxn= -qcalorimeter <(all the contents in the calorimeter)
-qcalorim=heat capacity of calorimeter x ∆T
-coffee cup calorimeter: a Styrofoam cup is used instead
-work is sometimes involved in reactions (system may do work on its surroundings or vice versa)
-Pressure-volume work: work involved in the expansion or compression of gases
W= < P is external pressure in bars/atm , A is surface area, h is distance, V is volume in L
-work is bar L, to convert to J: 1 bar L = J, 1 atm L = 101.325 J
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