Thermodynamics

Thermodynamics

the scientific study of the interconversion of heat and other kinds of energy

Thermochemistry

the study of the heat flow that accompanies chemical reactions; study of the relationships between chemical reactions and energy changes

Energy

ability to do work and transfer heat; directed change resulting from a process

Law of Conservation of Energy

total quantity of energy in the universe is assumed constant

Potential Energy

energy available by virtue of an objects position

Kinetic Energy

energy due to the motion of an object

heat

transfer of thermal energy between two bodies that are at different temperatures

system

part of the universe on which attention is focused

surroundings

rest of the universe

open system

exchange both energy and matter with its surroundings

closed system

exchange only energy with its surroundings, not matter

isolated system

cannot exchange either matter or energy with its surroundings

state function

properties that are determined by the state of the system regardless of how that condition was achieved; depend only on the initial and final states of the system and not on how the change is accomplished, potential energy

path function

properties or quantities whose values depend on the transition of a system from the initial state to the final state, work

stored energy

• within the boundary of the system

• independent of path

• they are thermodynamic properties

• internal, kinetic, potential energy

transit energy

• can cross the boundary of the system

• path dependent

• they are not thermodynamic properties; they are the forms that energy take to cross the system boundary

• heat, work

endothermic process

requires heat to be supplied to the system by the surroundings (S-L), (L-G), (S-G)

exothermic process

process that gives off heat or transfers thermal energy to the surroundings (L-S), (G-L), (G-S)

latent heat

energy that is absorbed or released during a phase change

sensible heat

refers to heat used to raise the temperature of a substance

Thermochemical Equation

represents chemical reactions and the heat involved in the reaction; consists of a balanced chemical equation (with physical states) and value of ∆H (constant-pressure reaction) or ∆E (constant-volume reaction)

Enthalpy (∆H)

an extensive thermodynamic property where the magnitude of heat involved depends on the amount of the reactant used in the reaction; it depends on the state

Hess’s Law

The total change in enthalpy in a chemical reaction is independent of its reaction mechanism

enthalpy of formation (∆Hf)

∆H associated with the formation of a compound from its constituent components

standard enthalpy of formation (∆H0)

standard heat formation; ∆H during the formation of 1 mole of the substance from its constituent elements, with all the substances in their standard states (standard state: 1 bar & 25C)

standard enthalpy of reaction (∆H0rxn)

∆H that accompanies a reaction at standard conditions; equal to the sum of the standard molar enthalpies of formation of the products minus the sum of the standard molar enthalpies of formation of the reactants