Solids, Liquids and Gases

1. Solids, Liquids and Gases Syllabus Title Lesson 01: Density Lesson 02: Brownian Motion Lesson 03: Pressure, Temperature and Volume

2. Solids, Liquids and Gases Solids, Liquids and Gases

3. Density09/11/2014 • Aims: • To experimentally find the density of different materials • To calculate the density of different materials • Starter: • Which has more mass honey or beer?

4. Density Definition: Density is a measure of how much mass of a substance is contained in a fixed volume. Symbol: ρ (rho) Equation: ρ = m or m = V ρ V Mnemonic: my violentrhino Units: kg/m3 m ρ V

5. What is the Mass of Air in the Room? • make a guess • Then Calculate: • density of air = 1.2 kg/m3 • If all the air the room was condensed into a liquid it would form a layer about 5mm deep

6. Measuring Density: Solids • Measure the mass • Measure the volume • Using a ruler (if regular shape) • Using Eureka Jars (by displacement of water) • In a measuring cylinder (by displacement of water) • Use ρ = m V Archimedes 287 – 212 BC

7. Measuring Density: Liquids • Measure the mass • Measure the volume using a measuring cylinder • use ρ = m V

8. Measuring Density • Measure the density of the materials available • Don’t forget water • Enter your results into a table and calculate the density

9. Densityrecap • Aims: • To experimentally find the density of different materials • To calculate the density of different materials

10. Brownian Motion09/11/2014 • Aims: • To describe the molecular structure of solids, liquids and gases • To explain brownian motion Starter: • draw the structure of a solid, liquid and gas in the back of your books

12. Solid • The atoms/molecules vibrate • atoms/molecules cannot move past each other • atoms/molecules are touching Melt freeze • Liquid • The molecules move around randomly • Molecules are touching sublime deposit Boil/ evaporate condense • Gas • The molecules move around randomly • There is a lot of space between the particles Handout

13. Brownian Motion First observed in 1785 by Jan Ingenhauz • If a small visible particle is observed in a fluid it will slowly move without any visible force being applied. • Examples: Smoke particles in air Pollen in water • Molecules in the air collide with the smoke particles randomly and it is moving due to the continually altering resultant force. Robert Brown (1773–1858) Movie Brownian Motion • Demo Brownian Motion • Brownian Motion (Video Clip 12) Albert Einstein (1879–1955)

14. Demo Diffusion • Bromine in Air • Coloured Water in Gas Jars

15. Diffusion

16. Diffusion • When particles are released in an enclosed area (i.e. smoke) they slowly disperse throughout the fluid (i.e. air). • This is due to collisions between molecules moving the particles of the smoke in a random direction. Movie Diffusion

17. What is Pressure?

18. What is Pressure?

19. What is Pressure?

20. Pressure • Definition: • molecules in a gas have a random motion • They hit a surface • When they hit they exert a force. • This force causes the pressure on a surface • Can increase the pressure by • more particles (more impacts, therefore more force) • Faster particles (harder impacts, therefore more force) • Smaller area • Symbol: p • Equation: p = F or F = p A A • Mnemonic: Put Foot on Ant orFluffy Pink Animals • Units: • Pascals, Pa • N/m2 • Note: Pressure is the same at all points in a fluid F p A

21. Questions • Calculate the pressure exerted by a 1000N elephant when standing on the floor if his feet have a total area of 1m2. • A brick is rested on a surface. The brick has an area of 2cm2. Its weight is 10N. Calculate the pressure. • A woman exerts a pressure of 100N/cm2 when standing on the floor. If her weight is 500N what is the area of the floor she is standing on? • Joe sits on a balloon. Joe weighs 500 N and the area of the balloon being sat on is 20 cm2. The balloon will pop if the pressure is greater than 20 N/cm2. Does it pop? • Jill weighs 600N, the femur bone in her thigh has an area of 4 cm2. What is the pressure in her thigh bone? She jumps from the first floor window effectively doubling her weight. Her thigh bones can each stand a pressure of 200 N/cm2. Will her bones withstand the impact? • Why is a sharp knife easier to use than a blunt knife • Why would a woman with stilettos damage a floor more than an elephant would?

22. Pressure Difference Separate Science Demo: • What will happen if the bottle of water is filled with water? • Why?

23. Pressure and Depth Separate Science • Pressure increases with depth • Pressure is the same in all directions at a certain depth • pressure difference = height × density × g • p = h × ρ × g • So the pressure difference in water (ρ=1000 kg/m3 is a lot greater than the pressure difference in the atmosphere ρ=1.2kg/m3)

24. Brownian Motionrecap • Aims: • To describe the molecular structure of solids, liquids and gases • To explain brownian motion

25. Pressure Temperature and Volume09/11/2014 • Aims: • To explain relationships between temperature, volume and pressure of gases • Starter: Copy and complete the table

26. Heating Gases • What happens to the kinetic energy of the particles when a gas is heated? • What happens to the pressure? gas gets hotter more kinetic energy more collisions at greater speed more pressure

28. Heating Gases If a gas is heated: • Molecules have more kinetic energy (KE) • Move faster • More collisions with the side at greater speed • More Pressure

29. Heating Gases What sort of graph would you get if you plotted ‘temperature (TC)’ against ‘the average kinetic energy (KEave) of the particles’. KEave -273 TC Movie Absolute Zero

30. Heating Gases If you increase the temperature (in Kelvin) what happens to the kinetic energy? KE Tk

31. Absolute Zero • If a gas is cooled the opposite happens • If it is cooled enough the particles stop moving • This happens at Absolute Zero (-273 °C) • The Kelvin Scale of Temperature starts at absolute zero • 1 K ≡ °C 0 -93 0 373 1027 Movie Thermometers

32. Pressure Law Separate Science • Sometimes called the Gay-Lussac Law, but normally the pressure law as he has another one named after him. • Gay Lussac published both the pressure and Charles’ Law. • Also established the method of measuring alcohol in drinks (ABV)

33. Pressure Law: Experiment Separate Science • Place a flask of air into a water bath. • Measure the pressure of the flask using a pressure sensor or Bourdon (pressure) Gauge • Change the temperature of the water bath in 5 K intervals. • Volume constant

34. Pressure Law Separate Science • Definition: • For a fixed mass of gas at a constant volume, the pressure is directly proportional to its absolute temperature • Equation: • p/T = constant • p1/T1 = p2/T2 • Where: • p is pressure in Pa • T is temperature in K • Notes: • Only works if temperature is in kelvin • Pa ≡ Nm-2 p (Pa) T (K)

35. Worked Examples Separate Science • We normally use the pressure law to compare pressures before and after. • As p/T = Constant thenp/T before = p/T after • Hence it is often written as: • p1/T1 = p2/T2

36. Question Separate Science • A solid sphere containing helium is at a pressure of 1 x 105 Pa and is then cooled from 400 K to 300 K. • What is the final pressure? p1 = 1 x 105 Pa T1 = 400 K T2 = 300 K p1/T1 = p2/T2 1 x 105 = p2 400 300 p2 = 1 x 105.300 400 = 7.5 x 104 Pa

37. Questions An airplane contains air at 9 x 104 Pa. During flight the temperature increases from 260 K to 290K. Assuming the volume of air does not alter, what is the change in pressure? A gas cylinder containing explosive hydrogen gas has a pressure of 5 x 106 Pa at a temperature of 300 K. The cylinder can withstand a pressure of 6 x 106 Pa before it bursts, causing a building-flattening explosion. What is the maximum temperature the cylinder can withstand before bursting? High pressure steam is used in a power station. The steam’s initial pressure is 5 x 105 Pa. After going through the turbine its pressure is 1 x 105 Pa. The steam’s final temperature is 150 C. What was its starting temperature assuming the volume of air is constant? A deep sea diver holds her breath as she surfaces. The pressure in her lungs is 4 x 105 Pa 30 m down and the temperature is 35 C. Atmospheric Pressure = 1 x 105 Pa. If she managed to keep the volume of air constant what temperature would the air in her lungs be when she surfaced? Separate Science

38. Robert Boyle Studied the cold and air Modern scientist he relied on experiments to prove his theories A Chemist and Physicist not an alchemist and a magician Robert Boyle 1627 - 1691

39. Boyles Law • A glass tube is filled with oil except for air at the top. • The pressure of the oil is increased shrinking the air column. • The gas is left to cool. • The pressure is dropped in stages and the volume measured once it has cooled down. • NB Temperature constant

40. Boyle’s Law V (m3) p (Pa) • Definition: • For a fixed mass of gas at a constant temperature, the volume is inversely proportional to the pressure. • Equation: • pV = constant • p1V1 = p2V2 • Where: • V is volume in m3 • p is pressure in Pa • Notes: • Mass must be the same (i.e. no particles escape) • T must be constant

41. Questions In the upper atmosphere a weather balloon has a volume of 50 m3. At ground level (1 x 105 Pa pressure) the volume is 20 m3. What is the pressure in the upper atmosphere A child takes a 0.01 m3 balloon from atmospheric pressure 1 x 105 Pa into an airplane containing air at 9 x 104 Pa. Assuming the temperature does not change what is the volume of her balloon? A climber carries a polystyrene flask up a mountain. The volume of the flask is 0.0002 m3 at sea level. The flask increases in size to 0.0003 m3. Assuming the temperature does not change. What is the pressure at the top of the mountain. A diver is 30 m below the surface where the pressure is 4 x 105 Pa. The volume of their lungs is 0.005 m3. What is the volume of air they could breathe out at atmospheric pressure? (assuming the temperature is constant).

42. Exam Questions

45. Explain the Following • How do hot air balloons work? • How can a small barbeque tank hold enough propane to cook with all summer long? • Why do helium balloons float • What will effect the time it takes to smell the perfume of a person who walks past you?