THERMODYNAMICS literally means “moving orevolving heat.” The science of thermodynamics is concernedwith heat and its transformation to mechanical energy.
SYSTEM - object or collection of objects under study. Everything else is referred to as surroundings The system and the surroundings constitute the universe.INTERNAL ENERGY- refers to the sum of the kinetics energies of the molecules of a body and the potential energy to intermolecular forces
REVERSIBLE PROCESS – one in which the system and its surroundings can be returned to their initial state before the process occurs
IRREVERSIBLE PROCESS - one in which the system and its surroundings cannot be returned to their initial state before the process occurs. Also known as the natural process.
ZEROTH LAW OF THERMODYNAMICS A B C“If object A is in thermal equilibrium withobject B and object A is in thermal equilibriumwith a third object C, then object B must be inequilibrium with object C”
Thermal Equilibrium- the main concern of the zeroth law, two bodies are said to be in thermal equilibrium if they have the same temperature.
THE FIRST LAW OF THERMODYNAMICS“When heat is added to a system, some of itremains in the system increasing its internalenergy, while the rest leaves the system as thesystem does work.”
THE SECOND LAW OF THERMODYNAMICS Three versions of the second law of thermodynamics: KELVIN-PLANCK STATEMENT – no heat engine can completely convert heat energy to work . In other words, there is no 100% efficient heat engine. CLAUSIUS STATEMENT – heat flows naturally from hot to cold objects . ENTROPY STATEMENT – when a reversible process occurs, the total entropy of the universe remains the same. When an irreversible process occurs, the total entropy of the universe increases.
Entropy is an abstract or theoretical quantity. Itis used to predict the direction of naturalevents and to predict whether a givenchemical or physical process is possible. Ifthe process is found to beimpossible, additional data may tell scientistwhat can be done to make the processpossible.
THE THIRD LAW OF THERMODYNAMICS“The entropy of a perfect crystal of a substance atthe absolute zero temperature is zero.”
HEAT ENGINESa device that converts heatenergy to mechanical work
TYPES OF HEAT ENGINES INTERNAL COMBUSTION ENGINE – burns the fuel inside the engine. EXTERNAL COMBUSTION ENGINE - burns the fuel outside the engine.
STEAM ENGINES HERO OF ALEXANDRIA – invented the oldest heat engine since 200 B. C. called Aeolipile in which steam was conducted through pipes from a boiler.
JAMES WATT –introduced a greatlyimproved steam enginewith a separatecondenser in 1769. Thisinvention triggered theso called “IndustrialRevolution” andstimulated theinventions of othertypes of engine.
GASOLINE AND DIESEL ENGINES The gasoline engine and dieselengine are internal combustionengines. These engines operate onfour different stokes:intake, compression, power andexhaust.
IDEAL HEAT ENGINEMaximum efficiency is obtained if allprocesses undergone by the workingsubstance of a heat engine are reversible.This statement is called Carnotprinciple, named after French engineerSadi Carnot. The Carnot engine is ahypothetical heat engine undergoing allreversible process.
WHAT YOU SHOULD KNOW:• You should know that efficiency is a comparison of the useful work energy provided by a machine or system to the work energy applied to the machine or system.• You should know that the formula for efficiency is: input work efficiency= x 100% output work• You should know that the parts of a machine or system and how they are connected together will affect the machines or systems efficiency.• You should know that other forces such as friction will affect an objects movement.• You should know that velocity ratio is a comparison of the distance a load moves to the distance travelled by the force needed to move it.