Chapter 2 - The First Law

Thermodynamics

The study of the transformations of energy

Open system

Can exchange matter and energy with its surroundings

Closed system

can exchange energy with its surroundings, but not matter

Isolated system

No matter or energy is exchanged with the surroundings

Work

Motion against an opposing force

Energy

Capacity to do work

Heat

Energy change due to a temperature change between the system and its surroundings

Exothermic process

Process that releases energy as heat into its surroundings

Endothermic process

Process in which energy is obtained from the surroundings

Thermal motion

Disorderly motion of molecules

Disorderly motion of molecules

It occurs due to heating

Internal energy

The total energy of a system, represented by U.

State function

A function where its value only depends on the current state of the system

First Law of Thermodynamics

The internal energy of an isolated system is constant

Expansion work

Work arising from a change in volume, whether it is positive (expansion) or negative (compression)

general expression for work

Free expansion

Expansion against zero opposing force, when Pex = 0

Expansion against constant pressure

Reversible change

Change that can be reversed by any modification of a variable

Heat transactions

Calorimetry

Study of heat transfer during chemical and physical processes

Calorimeter

Devise used for measuring energy transferred as heat

Adiabatic bomb calorimeter

Used to measure internal energy

Heat capacity

The slope of the tangent to the curve at any temperature.

Molar heat capacity at constant volume

The heat capacity per mole of material

Specific heat capacity

The heat capacity of the sample divided by the mass

Enthalpy (H)

State function

Isobaric calorimeter

A calorimeter used for studying processes at constant pressure

Adiabatic flame calorimeter

Used to measure the temperature change in a combustion reaction

Heat capacity at constant pressure

The slope of the tangent to a plot of enthalpy against temperature at constant pressure

Molar heat capacity at constant pressure

Heat capacity per mole of the material, its an intensive property

Thermochemistry

Study of the energy transferred as heat during a chemical reaction

Standard enthalpy change

The change in enthalpy for a process in which the initial and final substances are in their standard states

Standard state

Pure form of a substance at a specified temperature and 1 bar

Standard enthalpy of transition

Standard enthalpy change that accompanies a change of physical state

Standard enthalpy of vaporization

Enthalpy change per mole when a pure liquid at 1 bar vaporizes at 1 bar

Standard enthalpy of fusion

Standard enthalpy change accompanying the conversion of a solid to a liquid

Thermochemical equation

A combination of a chemical equation and the enthalpy change

Standard reaction enthalpy

Standard enthalpy of combustion

Standard reaction enthalpy for the complete oxidation of an organic compound to CO2 gas and liquid H2O

Hesss Law

The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divided

Standard enthalpy of formation

Standard reaction enthalpy for the formation of the compound from its elements in their reference states

Reference state

The most stable state of an element at the specified temperature and 1 bar

Reaction enthalpy of enthalpies of formation

Mean bond enthalpies

Average enthalpy change associated with the breaking of a specific A--B bond.

Kirchhoff’s Law

Path functions

Processes that describe the preparation of the state

Exact differential

An infinitesimal quantity that, when integrated, gives a result that is independent of the path between the initial and final states

Inexact differential

An infinitesimal quantity that, when integrated, gives a result that depends on the path between the initial and final states

Internal pressure

Expansion coefficient

The slope of the plot of volume against temperature at constant pressure

Isothermal compressibility

Measure of the fractional change in volume when the pressure is increased by a small amount

Joule-Thomson coefficient (µ)

Isenthalpic expansion

Expansion at constant enthalpy

Joule- Thomson effect

Cooling by isenthalpic expansion.

Isothermal Joule-Thomson coefficient

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