An Introduction into Thermodynamics Advanced Chemistry Ms. Grobsky

What is Energy?  Energy is the capacity to do work Thermal energy is the energy associated with the random motion of atoms and molecules Kinetic energy is the energy due to motion Potential energy is the energy available by virtue of an object’s position Chemical energy is the energy stored within the bonds of chemical substances Type of potential energy

UNITS OF ENERGY S.I. unit of energy is the joule (J) Heat and work (energy in transit) also measured in joules 1 kJ (kilojoule) = 10 3 J Calorie (cal) 1 cal is the energy needed to raise the temperature of 1 g of water by 1 o C 1 cal = J A food Calorie is actually a kilocalorie!

Work (w) is the transfer of energy that takes place when an object is moved against an opposing force A system does work when it expands against an external pressure Car engine Petroleum burns & produces gases which push out pistons in the engine and transfer energy to the wheels of car So, What is Work?

Energy Changes in Chemical Reactions - HEAT HEAT (q) is thermal energy that transfers from one object to another when the two things are at different temperatures and in some kind of contact Kettle heats on a gas flame Cup of tea cools down (loses energy as heat) Thermal motion or random molecular motion (temperature) is increased by heat energy Heat stimulates thermal motion Temperature = Heat

When dealing with energy, the world is divided into a system and its surroundings Open Mass & EnergyExchange: Closed Energy Isolated Nothing SYSTEMSURROUNDINGS 6.2

Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings. Endothermic process is any process in which heat has to be supplied to the system from the surroundings. 2H 2 (g) + O 2 (g) 2H 2 O (l) + energy H 2 O (g) H 2 O (l) + energy energy + 2HgO (s) 2Hg (l) + O 2 (g) energy + H 2 O (s) H 2 O (l) Exothermic versus Endothermic Reactions

Thermodynamics  Study of the relationships among heat, work, temperature, and energy  Focuses on energy  There are 3 laws of Thermodynamics  First Law of Thermodynamics is also known as Law of Conservation of Energy  The total energy of the universe is constant and can neither be created nor destroyed  It can only be transformed

Total Energy of System = Kinetic Energy + Potential Energy E = E K + E P Kinetic energy & potential energy are interchangeable by definition of Law of Conservation of Energy Ball thrown upwards slows & loses kinetic energy but gains potential energy The reverse happens as it falls back to the ground Total Internal Energy in General Terms

internal energy  The internal energy, E or U, of a sample is the sum of all the kinetic and potential energies of all the atoms and molecules in a sample  It is the total energy of all the atoms and molecules in a sample Total Internal Energy in Chemistry Terms

More on INTERNAL ENERGY (E) Internal energy changes when energy enters or leaves a system E = E final - E initial E change in the internal energy Signs (+/-) will tell you if energy is entering or leaving a system + indicates energy enters a system - indicates energy leaves a system

+= Change in internal energy Energy supplied to system as heat Energy supplied to system as work E = q (heat) + w (work)  Sign conventions for q and w  Heat is transferred from the surroundings to the system  q is +  Work is done on the system by the surroundings  w is +  Heat is transferred from the system to the surroundings  q is -  Work is done on the surroundings by the system  w is - Heat and work are two equivalent ways of changing the internal energy of a system