Physics and chemistry for 3r_ESO. What they deal with?. System. Change in the system.

1. PHYSICS AND CHEMISTRY

3. System: It is what we want to study Surroundings: They are everything else but the system System: Water Surroundings Boundary –The system and surroundings are separated by a boundary. It may be fixed, movable or imaginary.

4. MATTER ENERGY ENERGY OPEN CLOSED ISOLATED Types of systems

5. System State 1 System State 2 Change Change

6. 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

7. Change Liquid: water T 1 = 30º C m 1 = 150 g Atmospheric pressure: 1 atm Density: ? Liquid: water T 2 = 120º C m 2 = 135 g Atmospheric pressure: 1 atm Density: ? Heating

8. 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 T 2 = 120º C m 2 = 135 g Atmospheric pressure: 1 atm Density: ? Pure water boils at 100º C !!!!

9. 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?

10. 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?

11. The class as a system Pupils: 27 seated Time: 10:10 am Date: January 25th, 2010 Teacher’s chair:1 Atm. Pressure: 1 atm Teacher’s desk:1 Chalk: 2 pieces Ambient sound: 20 dB (decibels) Desks: 28 ,, Chairs: 28 Room Temperature: 19ºC Windows: All closed Teachers: 2 Blackboard: Clean Date: January 25th, 2010 Time: 10:43 am Desks: 28 ,, Chairs: 28 Pupils: 25 seated Teacher’s desk:1 Teacher’s chair:1 Teachers:1 Room Temperature: 15ºC Atm. Pressure: 1 atm Chalk: 0,5 pieces Blackboard: Written Ambient sound: 40 dB (decibels) Windows: 1 opened (just a bit) CHANGE Exercise: List the variables that have changed with its value before and after .

12. The class as a system Date: January 25th, 2010 Time: 10:10 am Desks: 28 ,, Chairs: 28 Pupils: 27 seated Teacher’s desk:1 Teacher’s chair:1 Teachers: 2 Room Temperature: 19ºC Atm. Pressure: 1 atm Chalk: 2 pieces Blackboard: Clean Ambient sound: 20 dB (decibels) Windows: All closed Date: January 25th, 2010 Time: 10:43 am Desks: 28 ,, Chairs: 28 Pupils: 25 seated Teacher’s desk:1 Teacher’s chair:1 Teachers: 1 Room Temperature: 15ºC Atm. Pressure: 1 atm Chalk: 0,5 pieces Blackboard: Written Ambient sound: 40 dB (decibels) Windows: 1 opened (just a bit) CHANGE

13. We need to explain the changes our system has undergone Time: ? Pupils: ? Teachers: ? Temperature: ? Chalk: ? Ambient sound: ???

14. 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: ???

15. 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?

16. 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.