Unit 6: Thermochemistry

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39 Terms

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enthalpy

the heat exchanged at constant pressure

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system

the part of the world that is being studied

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surroundings

everything else around the system

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universe

the system and the surroundings together

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heat (q)

a form of energy that flows between two samples of matter because of their differences in temperature

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work

the energy needed to move something against a force, equal to -PĪ”V

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endothermic

heat is absorbed by the system from the surroundings; includes melting, boiling, vaporization, sublimation; breaking bonds; ā€œtakes to breakā€

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exothermic

heat is released from the system to the surroundings; includes freezing, condensation, deposition; making bonds; ā€œfrees to formā€

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solvent or solute overcomes IMFs

endothermic process

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solute and solvent recombine

exothermic process

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solution temperature change

based on the temperature change of the surroundings

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1st law of thermodynamics

energy cannot be created or destroyed, energy is released to/taken from the surroundings

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activation energy

used to break bonds and/or IMFs

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catalysts

added to reactions to increase the reaction rate, only affects activation energy, not enthalpy

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temperature

measure of the average kinetic energy of the particles

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kinetic energy formula

KE=1/2mv2

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heat transfer

the transfer of energy from hotter particles to colder particles upon collision

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thermal equilibrium

two substances result in the same temperature after heat transfer

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energetically favorable reactions

exothermic reactions

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lower potential energy

more stable

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specific heat capacity (c)

amount of energy needed to raise the temperature of one gram of a substance by 1 degree C or 1 K

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calorimeter

measures the amount of heat transferred during a reaction, a device that stops the transfer of heat between the inside of the coalorimeter and the surroundings

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calorimetry

the measurement of the quantify of heat exchanged

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heat calculation formula

qlost=-qgained

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solid

low potential energy, requires energy to become liquid

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liquid

medium potential energy, requires energy to become gas, releases energy to become solid

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gas

high potential energy, releases energy to become liquid

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enthalpy of fusion

involves going from solid to liquid and vice-versa

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entahlpy of vaporization

involves going from liquid to has and vice-versa

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constant-pressure calorimeter

made of two styrofoam cups, outer cup insulates, two solutions are mixed inside, heat produced/absorbed is measured with thermometer

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constant-volume bomb calorimeter

filled with oxygen gas before being placed in bucket, sample is ignited electrically and heat can be determined by the temp increase of the surrounding water

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given Ī”H values

always based on the molar coefficient for the reaction as written

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bond energy

the enthalpy changed required to break or form a given bond in one mole of gaseous molecules

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Ī”HĀ°

signifies that it is standard state, which is 1 mol, 1 atm, and typically 298K (25 Ā°C)

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0 kJ/mol

standard enthallpy of element in its most stable form

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Ī”HĀ°f

energy change that occurs with the formation of 1 mole of a substance

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Ī”HĀ°rxn

energy change that occurs for a reaction

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Hessā€™s Law

shows the energy changes associated with a combination of steps that leads to a overall reaction

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Hessā€™s Law 3 Properties

  1. heat is directly proportional to the amount of products and reactants in a reaction

  2. if the reaction is reversed, the sign of the heat is also reversed, but the amount of heat is the same

  3. in going from a particular set of reactants to a particular set of products, the change in enthalpy is wlasy the same, regardless of the route taken