Kinetic Molecular Theory

1. Kinetic Molecular Theory

2. Kinetic Molecular Theory • Kinetic Molecular Theory – is the idea that matter is made from moving invisible particles. • The following are the principals of Kinetic Molecular Theory: • All matter is made up of tiny particles • Different substances have different particles • The particles are in constant motion • The more energy the particles have, the faster they move. • The attraction between particles decreases with an increase in distance.

3. Solid

4. Liquids

5. Gas

6. Change of State • The change of state only happens when you add or remove energy. • What we experience as heat, molecules experience as vibration. • An increase in movement of particles results in the melting or sublimation of a solid, and evaporation of a liquid. • The reduction in movement of particles results in the condensation or deposition in gases and solidification in liquids.

7. A word on sublimation and deposition • Sublimation, and deposition, is the ability to turn a solid into gas or a gas into a solid without passing through the liquid stage. • In order for this to occur you need to have an object reach a specific temperature and a specific pressure. • The point in which sublimation and deposition is called the triple point. The point on a pressure vs temperature graph where solid, liquid and gas meet.

8. Triple point of Water and Carbon Dioxide • Water’s triple point – where a solid piece of water, liquid and gas can all co-exist - is at 273.16 K (0.01º C) and a pressure of 611.73 pascals (.006 atm). It isatthis point where water in a solidform and has a gascoming off of it. • Dry ice’s (Carbon dioxide’s) triple point is 518 kPa (kilopascals) and -56.6ºC or 216.55 Kelvin.

9. Phase Diagram of H2O 218 S L S L p (atm) 1 Triple Point L G .006 G S  G 100 374 0 .01 T (oC)

10. Phase Diagram of CO2 S L S Critical Point L 73 p (atm) L G Triple Point 5.1 G 1 S  G -78 -57 31 T (oC)

11. Water • Lets take water for a moment: • When it is in a solid form and we add energy (heat) we notice that the molecules vibrate a lot and turns into a liquid. • When it is in a liquid form and we add energy (heat) we notice that the molecules vibration increases and turns into a gas. • But if we cool the molecule at any stage, we slow down the vibration of the molecules and can reverse the process.

12. Explaining Dissolving • The kinetic molecular theory perfectly describes how compounds, like sugar, dissolve in water. • When water is in a liquid state, the molecules are vibrating and have space between them for sugar to enter into the water and dissolve. • If you increase the heat of the water, the vibration of the water molecule increases, thus more space is created between the water molecules. • Thus sugar has more space to enter in between the water molecules and thus the sugar will dissolve a lot faster.

13. Explaining Density • Problem, why is it that the density of water in solid form has a different density when it is in liquid form and a different density when it is in a gas form? • Answer, the kinetic molecular theory. • When you add energy to a particle and increase the vibration of the particle the particles in the compound expands and thus the volume changes. • If the volume increases and the mass stays the same, the density decreases and viola, we now know exactly why ice floats in water.

14. Finally…. • Ever notice on sidewalks and on train tracks there are gaps between the concrete sidewalk and concrete road? • Well kinetic molecular theory explains why we need this. • If a sidewalk was one solid strip without any gaps, during cooler months the sidewalk contracts and during warmer months the sidewalk expands. • This constant motion of contraction and expansion leads to the sidewalk cracking or buckling. • If you put in gap when laying the concrete, you mitigate and minimize the amount of cracks that will be created.