PHYSICS AND CHEMISTRY

Definition It is the study of MATTER, what it is made

of, how it behaves, and the changes it is subjected to.

It trys to observe phenomena and explain them through laws that can be applied to the world around us.

System: It is what we want to study

Surroundings: They are everything else but the system

System: WaterSurroundings

BoundaryBoundary –The system and surroundings are separated by a –The system and surroundings are separated by a boundary. It may be fixed, movable or imaginary.boundary. It may be fixed, movable or imaginary.

MATTER ENERGY

ENERGY

OPEN CLOSED ISOLATED

Types of systems

System

State 1

System

State 2Change

Change

To try and understand what has happened, we need information about the system before and after the CHANGE.

We have to gather information for states 1 and 2

How can we get this information??

By accurate measure of different variables in each state.

Temperature Pressure Weight

Change

Liquid: water

T1 = 30º C

m1 = 150 g

Atmospheric pressure: 1 atm

Density: ?

Liquid: water

T2 = 120º C

m2 = 135 g

Atmospheric pressure: 1 atm

Density: ?

Heating

After collecting the information we need, we can start thinking and giving a SCIENTIFIC explanation about what has happened.

First of all it is good to check the collected data to spot some errors (according to our previous knowledge)

Liquid: water

T2 = 120º C

m2 = 135 g

Atmospheric pressure: 1 atm

Density: ?

Pure water boils at 100º C !!!!

Then we are prepared to : answer questions, make predictions, etc

1.- Why has the mass of water decreased ?

2.- Do all liquids boil at the same temperature?

3.- What are the “bubbles” ?

4.- When heating a liquid, will its temperature always increase?

5.- Make a prediction about the temperature after 10 minutes

6.- Has the system increased or decreased its energy?

Some variables may have not change its value; in this case the atmospheric pressure has not changed. But ...

7.- Has the atmospheric anything to do with boiling?

We don’t have information about the density of our system

8.- Will it change during the boiling process?

9.- What is the density of a substance?

The class as a systemPupils: 27 seatedTime: 10:10 amDate: January 25th, 2010Teacher’s chair:1Atm. Pressure: 1 atmTeacher’s desk:1Chalk: 2 piecesAmbient sound: 20 dB (decibels)Desks: 28 ,, Chairs: 28Room Temperature: 19ºCWindows: All closedTeachers: 2Blackboard: Clean

Date: January 25th, 2010Time: 10:43 amDesks: 28 ,, Chairs: 28Pupils: 25 seatedTeacher’s desk:1Teacher’s chair:1Teachers:1 Room Temperature: 15ºCAtm. Pressure: 1 atmChalk: 0,5 piecesBlackboard: WrittenAmbient sound: 40 dB (decibels)Windows: 1 opened (just a bit)

CHANGE

Exercise: List the variables that have changed with its value before and after.

The class as a system

Date: January 25th, 2010Time: 10:10 amDesks: 28 ,, Chairs: 28Pupils: 27 seatedTeacher’s desk:1Teacher’s chair:1Teachers: 2Room Temperature: 19ºCAtm. Pressure: 1 atmChalk: 2 piecesBlackboard: CleanAmbient sound: 20 dB (decibels)Windows: All closed

Date: January 25th, 2010Time: 10:43 amDesks: 28 ,, Chairs: 28Pupils: 25 seatedTeacher’s desk:1Teacher’s chair:1Teachers:1 Room Temperature: 15ºCAtm. Pressure: 1 atmChalk: 0,5 piecesBlackboard: WrittenAmbient sound: 40 dB (decibels)Windows: 1 opened (just a bit)

CHANGE

We need to explain the changes our system has undergone

Time: ?

Pupils: ?

Teachers: ?

Temperature: ?

Chalk: ?

Ambient sound: ???

We need to explain the changes our system has undergone

Time: Just time passing by

Pupils: They’ve gone to the bathroom They’ve been thrown out of the class They are with one of the two teachers

Teachers: He/She is in the lab He/She is with the two pupils

Temperature: Cold air entered through the open window Central heating (if any) is not working

Chalk: Someone has written on the blackboard A student has thrown a piece out of the class (opening the window)

Ambient sound: ???

Sometimes is easy to explain a change but sometimes it is not. We need to do more research or measuring

Chalk: Someone has written on the blackboard A student has thrown a piece out of the class (opening the window

What would you do to prove the right explanation?

Now it’s your turn to scientifically study systems and its changes.

1.- You have to define your system and surroundings

2.- You have to check the variables you have

3.- You have to answer the questions or try to explain the material and energetic changes

4.- It is important to take the “correct” point of view.