Lecture 1: Introduction to Physical Chemistry

physical chemistry

• systematic application of the methods of physics to study chemical systems

• development of principles and theories that explain and interpret the behavior of chemical systems

• applications of physical chemistry

  • chemical systems

  • microscopic - based on the concept of molecules

  • macroscopic - large scale properties of matter without use of the molecule concept

• divisions of physical chemistry

  • quantum chemistry - concerned with properties of molecules and their reactions and its applications on molecular bonding, atomic structure, and spectroscopy

  • statistical mechanics - provides a molecular insight to the laws of thermodynamics and allows the calculation of macroscopic thermodynamic properties from molecular properties

  • thermodynamics - the science of energy and how energy transforms, it involves heat and work and the changes they produce in the states of the system

  • kinetics - the study of the rate processes such as chemical reactions, diffusion, and flow of charge in an electrochemical cell

thermodynamics

• the study of the interrelation between heat, work, and internal energy of a system and its interactions with its environment.

• examples of systems:

  • gas in a container

  • charging and discharging a battery

  • chemical reactions

system and surroundings

• system - quantity of matter or region in space chosen for study with constant mass but possible variable volume

• surrounding - mass or region outside the system

• boundary - surface separating system from surroundings

at a given temperature, a system has the following properties:

• kinetic energy (KE) - energy associated with motion

• potential energy (PE) - energy associated with its position in a field (involving gravity)

• internal energy (U) - energy associated with microscopic kinetic energies and the energy of interactions between microscopic components as the microscopic kinetic energy increases with temperature

the following are distinguished from the system

• control volume - fixed volume over which mass can pass in and out of its boundary

• control surface - boundary of the control volume

comparison of system and control volume:

• system - fixed mass but variable volume and closed

• control volume - fixed volume but potentially variable mass and open

thermodynamic boundary

• the obvious separation between system and surroundings

• types of thermodynamic boundaries:

  • adiabatic (thermal conducting) or non-adiabatic

  • rigid or non-rigid (moveable)

  • permeable (allows matter to pass through) or impermeable

thermodynamic systems

• closed system - does not have mass flow across the boundary, only energy flow

• open system - has both mass and energy flow across their boundaries

• isolated system - no interaction between system and surrounding, therefore neither mass nor energy can be transferred across their boundaries

thermodynamic states

• state variable - describes the state of a system at time t, but it does not reveal how the system was put into that state

  • pressure

  • temperature

  • volume

  • moles

  • internal energy

thermodynamic equilibrium

• no changes within the system as the macroscopic properties remain constant with time

• for there to be thermodynamic equilibrium, all types of equilibrium must be present:

  • thermal equilibrium

  • mechanical equilibrium

  • chemical equilibrium

  • phase equilibrium

thermal equilibrium

• a system and its surroundings are in thermal equilibrium if there must be no change in properties of the system or surroundings when they are separated by a thermally conducting wall

• temperature

  • a property that describes the flow of energy

  • energy will flow between two objects in contact, resulting in change of state of these two objects

  • the energy flows from the object with a higher temperature until some equilibrium condition is established

• separatory boundaries:

  • diathermic - if a change of state is observed when two bodies are brought into contact with one another

  • adiabatic - if no energy flow is permitted between the two objects in contact

• zeroth law of thermodynamics

  • if A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C is also in thermal equilibrium with A

• thermodynamic temperature scale is Kelvin

mechanical equilibrium

• related to pressure

• there is no change in pressure at any point of the system with time

• whenever the net force on an object is zero, the object is in mechanical equilibrium

• pressure exerted by gases

  • gases can be stored in two separate containers separated by a movable wall. the higher pressure gas will move the wall and compress the lower pressure gas until an equilibrium is established

  • pressure of gases may be controlled via gas entry and release valves, that are set or controlled to let gases in and out at certain pressure thresholds

chemical equilibrium

• no net chemical reactions occurs in the system

• no net transfer of matter from on part of the system to the other

• concentration of chemical species in the various parts of the system are constant with time

thermodynamic processes and cycles

systems undergo the following:

• change of state - implies one or more properties of the system has changed

• process - a succession of changes of state, it is assumed that processes are all sufficiently slow such that each stage of the process is near equilibrium

• cycle - series of processes that returns to the original state

• isothermal - constant temperature

• isobaric - constant pressure

• isochoric - constant volume

thermodynamic properties

• intensive variable

  • independent of the amount of mass of the system

  • pressure, temperature, specific volume, density

• extensive variable

  • dependent on the size of the system

  • total volume, mass

temperature

• a thermodynamic property that determines the direction of heat flow

• ice point - temperature equilibrium between pure ice and liquid water with air saturated with vapor (0°C at 1 atm)

• steam point - temperature equilibrium between pure liquid water and water vapor (100°C at 1 atm)

• celsius scale

  • temperatures are denoted as theta and expressed in degrees celsius

pressure

• the amount of equal force applied to a specific area

• barometer

  • invented by torricelli, it is a device used to measure pressure

  • when the column of mercury is in equilibrium with the atmosphere, the pressure at the base is equal to that from the atmosphere, so the height of the mercury is a measure of the external pressure

• manometer

  • a simple pressure measuring device in which a non-volatile viscous liquid is contained in a U-tube

  • the pressure in the apparatus or from the atmosphere is directly proportional to the height difference of the two columns

  • formula:

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• gauge pressure - pressure relative to atmospheric pressure

• absolute pressure - the sum of the gauge pressure and the atmospheric pressure

• formula:

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• note: on thermodynamics, we are almost always concerned with absolute pressure as opposed to gauge pressure, and absolute pressure is nearly always interpreted as P

volume

• the amount of space that matter occupies

• molar volume - volume occupied by 1 mole of gas in a given set of conditions

• formula:

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measurements

• quantity - a property that is measured

• unit - a standard quantity against which a quantity is measured

base units:

• length

• mass

• time

• temperature

• amount of substance

• electric current

derived units

• frequency

• energy

• force

• pressure

• power

• electric charge

• electric potential difference

• area

• volume

• density

• absorbance