AP Chemistry - Unit 6: Thermodynamics

Thermochemistry

the study of energy changes that occur during chemical reactions and changes in state

Heat

The energy transferred between objects that are at different temperatures (represented by Q)

Exothermic Reaction

Chemical Reaction in which energy is primarily given off in the form of heat

-q

system releases heat

Endothermic Reaction

Chemical Reaction in which energy is primarily absorbed in the form of heat

+q

system gains heat

System

a part of the universe on which you focus your attention (usually the chemical reaction itself)

Surroundings

everything else in the universe outside of the system

universe

the system plus the surroundings

internal energy of a system (U)

is the sum of the potential and kinetic energies of the components in the system

work

force x distance, expressed in joules

-w

work done by the system

+w

work done on the system

Energy

the capacity to do work

Joules

unit of energy

specific heat

The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree celcius

heat capacity

the number of heat units needed to raise the temperature of a body by one degree.

Specific Heat (Equation)

q = mcΔT

heat transfer

the movement of energy from a warmer object to a cooler object

thermal equilibrium

The state of two or more objects or substances in thermal contact when they have reached a common temperature

molar heat capacity

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

heat of vaporization

The amount of energy required for the liquid at its boiling point to become a gas

heat of fusion

Amount of energy required to change a substance from the solid phase to the liquid phase.

Enthalpy

the heat content of a system (total energy)

Enthalpy of Reaction

the quantity of energy transferred as heat during a chemical reaction (usually in moles)

Bond Enthalpies

bonds broken - bonds formed, energy associated for the creation of products by formation of bonds

Enthalpies of Formation

the enthalpy change for the reaction in which a compound is made from its constituent elements in their elemental forms

Enthalpy of formation Equation

ΔHoreaction = Σ∆Hfoproducts − Σ ΔHforeactants

state function

property of a system, such as temperature and pressure, that depends on the beginning and end not the process of which it undergoes

Hess's Law

if a reaction is carried out in a series of steps, ∆H for the overall reaction equals the sum of the enthalpy changes for the individual steps

first law of thermodynamics

The energy of the universe is constant. Energy can be transferred and transformed, but not created or destroyed. (AKA principle of conservation of energy, 143)

second law of thermodynamics

Every energy transfer or transformation increases the entropy of the universe. For a process to occur spontaneously, it must increase the entropy of the universe

Entropy

The quantification of a measure of disorder or randomness