AP Chemistry - Thermochemistry 1

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27 Terms

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Thermochemistry

the study of energy and its interconversions chemical reactions and physical processes.

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Energy

Capacity to do work or produce heat

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Kinetic Energy Of Motion

½ mass velocity squared; the energy an object possesses due to its motion.

KE = 3RT/2

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Potential Energy

Energy that can be converted to useful work or energy die to the composition toits position or state.

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ON EARTH potential energy

PE = (mass)(height of object)(g from a ref.pt)

Acceleration due to gravity - 9.81 meter/sec squared.

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Heat

Involves the transfer of energy between 2 objects

Due to a temperature difference

  • Represented by q

  • Energy measures in joules ( 1 calorie = 4.184 joules)

  • J = kg x m²/s²

  • 1 kJ = 1000 J

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work

force x distance something is moved

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State Function

a property independent of pathway

  • sometimes called intensive property

  • this property does not depend on amount of substance.

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Examples of State Functions

  • energy change of a system

  • specific of a substance

  • temperature

  • density

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Extensive Property

depends directly on the amount of substance present

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Example of Extensive Property

  • Mass

  • heat

  • work

  • length

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Universe

made of a system and the surroundings

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System

the reaction we are focusing on

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Surroundings

everything else in the universe not in the system. In a solution, the solvent is part of the surrounding.

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Exothermic

energy in the form of heat flows OUT of the system

Energy is released to the surrounding as heat

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Endothermic

energy as heat flows INTO a system

Energy is absorbed from the surroundings as heat

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specific heat

The energy required to raise the temperature of one gram of a substance 1 degree Celsius

ex. specific heat water = 4.184 J/CxG

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Calorie

amount of heat required to raise 1 gram of pure water 1 C

  • (note : one nutritional Calorie is kcal and begins with a capital C)

  • 1 calorie = 4.284 J

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Molar Heat Capacity

the energy required to raise the temperature of one mole of substance by 1 degree Celsius

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Enthaply

  • heat content of a system at constant pressure

  • State function

  • Most cases enthalpy is equal to q at constant pressure

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Work

force x distance something moves

  • Distance is in meters

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In a cylinder

  • Work done by the piston and cylinder = (P)(volume of the cylinder)

  • (P)(V) = (F)(D) - both measure energy because both are equal to work

***** FOR AN IDEAL GAS*******

  • work for closed system = -P V at constant pressure

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Gas may expand

If a system expands = positive work on surrounding and negative work of the system.

The system Is releasing (exothermic) heat energy and the surrounding Is absorbing (endothermic) the heat energy.

  • -w = P V or w = -P V

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A gas may contract

  • negative work on surroundings and positive work on the system.

  • w = -P V

the surrounding is releasing (exothermic) heat energy and the system is absorbing (endothermic) the heat energy.

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Sign convention

In thermodynamics you must have a sign + a number and a unit.

  • the sign represents the system pov

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Internal Energy of System

  • This is the sum of the kinetic and potential energies of all the particles of the system

    •  E = q + w

    • change in energy = heat + work

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The First Law Of Thermodynamics

the energy of the universe is constant