Thermodynamics

What is Temperature

• Temperature is a measure of the kinetic energy of matter.

• Collision between molecules causes energy transfer

• Motion of molecules causes pressure (collisions with container).

• KE = (½mv2)av = 3/2 kBT

Particles of matter are in constant motion. This motion relates directly to the state of matter of the object (solids, liquids, or gases).

TemperatureTemperature affects how fast these particles move. The higher the temperature the faster the particles move. Moving particles possess kinetic energy.

TemperatureTemperature is defined at the average kinetic energy of the particles of an object.

Temperature

• Temperature– measure of the

average KE of the particles in a sample of matter

Zero Degrees

• Absolute Zero (Kelvin Scale) (-273.15 oC)

• No motion of molecules• Pressure is Zero.

What is Heat?

• Heat is Thermal Energy• Energy transferred between two objects because of

temperature difference.• 1 calorie is the heat required to raise the temperature of

one gram of water by one degree Celcius.• 1 cal = 4.186 Joules• Work is Energy. Heat is generated in mechanical

processes. • Known as MECHANICAL EQUIVALENCE OF HEAT

Thermal Energy

• Thermal Energy– the total energy of the particles in a material– KE - movement of particles– PE - forces within or between particles due to

position– depends on temperature, mass, and type of

substance

Thermal Energy Transfer

• Heat– thermal energy that flows from

a warmer material to a cooler material

• Like work, heat is...– measured in joules (J)– a transfer of energy

Thermal Energy Transfer• Why does A feel hot and B feel cold?

80ºC

A

10ºC

B

– Heat flows from A to your hand = hot.

– Heat flows from your hand to B = cold.

Thermal Energy Transfer• Heat is always

transferred from hot to cold.

• Insulators slow the transfer of heat due to air pockets.

• Conductors easily allow the transfer of heat, like metals.

• Heat is transferred by conduction, convection, and radiation.

Three Ways to Burn Yourself•Conduction (Direct thermal

transfer through atomic excitation.)

•Convection (Heat Rises.

Thermal Energy is carried by

moving particles (air, water, etc.

Caused by density changes)

•Radiation (photons carry energy

and collide with other material)

Thermal Energy Transfer

• Specific Heat (Cp)

– amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin

– units: J/(kg·K)or J/(g·°C)

Thermal Energy Transfer• Which sample will take

longer to heat to 100°C?

50 g Al 50 g Cu

• Al - It has a higher specific heat.• Al will also take longer to cool down.

Metals require little energy to raise its temperature.

Thermal energy can be calculated using the following formula:

Try this one!! Answer = 376 J/kg K

Did you do this problem?

Thermal Energy Transfer

Q = m T Cp

Q: heat (J)m: mass (kg)T: change in temperature (K or °C)Cp: specific heat (J/kg·K or J/g.oC)

T = Tf - Ti

– Q = heat loss+ Q = heat gain

Heat Transfer

• Calorimeter– device used to

measure changes in thermal energy

Coffee cup Calorimeter

– in an insulated system,

heat gained = heat lost

0th Law of Thermodynamics

• Thermal Equilibrium is the condition where there is no net heat flow between two bodies that have been placed in thermal contact.

• If A is in thermal equilibrium with B and

• C is in thermal equilibrium with B then

• A is in thermal equilibrium with C

FIRST LAW OF THERMODYNAMICS

• Q = Heat transferred TO a system

• W = Work done BY a system

• U = Internal Energy of a system

U = Uf – Ui = Q – W

First Law

• PRINCIPLE of CONSERVATION of ENERGY

• In a cyclic system (where the system is the same at the end as at the beginning)

U = 0

• Q = W

2nd Law of Thermodynamics

• Heat Energy, on its own, flows from Hot to Cold

• Heat Energy does NOT spontaneously flow from cold to hot

2nd Law of thermodynamics Fancier wording

• It is impossible to construct a heat engine that, operating in a cycle, produces no other effect than the absorption of heat from a reservoir and the performance of an equal amount of work.

Heat Engine

• Generalized Thermodynamic Engine

• Must be T to get work done

• There is always loss of Heat to environment

Thermal Efficiency

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