Drill December 17, 2015Identify which of the two descriptions of

your class is an intensive property and which is extensive:

The number of students in the class. The grade level of the students in class.

Define the following: Thermodynamics System Property

DrillFill in the blanks: “Dynamis” is Greek for ________.

Matter and Energy

Objectives: SWBAT:1. Differentiate between Closed and Open Systems; Intensive and Extensive Properties; Property and State.

Matter and EnergyThis course is an introduction to the study of thermodynamics and an investigation of how it can be applied to renewable and non-renewable energy sources.

Thermodynamics - study of systems and energy transfer

System – what we choose to studyBoundary – separates system from surroundingsSurroundings – everything outside of system

Matter and EnergyThere are two types of systems…Closed Systems – no mass crosses the boundaryOpen Systems – mass crosses the boundary

Thermodynamics - “the study of systems and energy transfer”

“Energy can cross the boundary of both open and closed systems.”

Energy in… Energy out…

Matter and EnergyThere are two types of properties:Property – a characteristic used to describe a

system

1) Extensive – the whole equals the sum of its parts

MassVolume

TemperaturePressure

2) Intensive – the whole is the same as any partEXTENSIVE

INTENSIVE

Mass and Volume are both extensive properties.Temperature and Pressure are intensive properties.

Extensive properties usually use capital letters as symbols.Extensive properties usually use lower case letters as symbols.

Mass, Temperature and Pressure are exceptions to the rule:Mass (m) is extensive; Temperature (T) and Pressure (P) are intensive.

Matter and EnergyProperty – a characteristic used to describe a

systemProperty Symbol

Definition

Mass m measure of the amount of material present

Volume V amount of space occupied by an object

Energy E the ability to do work or produce heatTemperature

T measure of the molecular activity of a substance

Pressure P force exerted per unit area on the boundaries of a substance

Density ρ the total mass of a substance divided by the total volumeWhat type of property is

density, ρ?What type of property is energy, E?

IntensiveExtensive

Matter and EnergyProperty – a characteristic used to describe a

system

When an extensive property is made intensive by dividing by mass, we use a lowercase symbol and the prefix “specific”.

In general, an extensive property can be made intensive by dividing by the mass of the system.

Extensive Divide by Mass

Intensive

EnergyE

kilojoules, kJ

Energy/massE/m

kilojoules/kilogram

Specific Energye

kJ/kg

HOMEWORKDefine the following properties:Specific volumeDensitySpecific gravity Humidity

Matter and Energy

Specific volume: is the total volume of a substance divided by the total mass of that substance. .. Units ?

Matter and Energy

Density: is the total mass of a substance divided by the total volume occupied by that substance… Units?

Matter and Energy

Specific gravity: is the measure of the relative density of water at a standard temperature. For engineers we use the temperature of 60deg. F

Matter and Energy

Humidity: is the amount of moisture (water vapor) in the air. It can be expressed as absolute or relative humidity. Absolute humidity is the mass of water vapor divided by a unit of volume of air (g of water/ cm3 of air. Relative humidity is expressed as a %.

Matter and EnergyProperty – a characteristic used to describe a

systemLet’s work an example:

A closed steel tank contains 3 kg of water in the form of vapor and liquid. The volume of the tank is 18 m3. Calculate the specific volume of the water in the tank:

v=18 m3 , m= 3 kgv=V/mv=18m3 /3 kg

v= 6 m3 /kg

Matter and EnergyProperty – a characteristic used to describe a

systemA closed steel tank contains 3 kg of water in the form of vapor and liquid. The specific energy of the water in the tank is 126 kJ/kg. Calculate the total energy of the water in the tank:

E=126 kJ/kg, m= 3 kg

Specific Energy (e) = Energy/massEnergy= Specific Energy X MassE = e x m E = 126 kJ/kg x 3 kg

E = 378 kJ

Matter and EnergyThere are two types of properties:Property – a characteristic used to describe a

system

1) Extensive – the whole equals the sum of its parts2) Intensive – the whole is the same as any part

We now know that properties help to describe systems, that there are extensive and intensive properties, and how to convert from intensive to extensive and vice versa.

To truly describe a system, you must be able to list all of the properties of that system…you must know the state of that system.

State – a list of all the property values of a system

But properties can change over time; when any property changes, the state of the system also changes.

Matter and EnergyProperty – a characteristic used to describe a

system

You can think of the state of the system as a snapshot, a picture, of all of the property values of a system at some point in time.

State – a list of all the property values of a system

Temperature

Pressure

Mass

Energy

A snapshot of the dashboard of a car would tell you the state of the car at that point in time.Let’s say you take your car out for a drive. As you drive, you burn fuel (lose mass), your engine heats up(temperature)…

If someone took pictures as you drove, they would capture a record of a series of states for your car. That record of states is a process.

...the oil pressure climbs (pressure), etc. In short, the state of your car changes as you speed up and slow down.

Process– a record of all the states that a system passes through

1 2 3

4 5 6State

Process