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PHASE CHANGES.

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Presentation on theme: "PHASE CHANGES."— Presentation transcript:

1 PHASE CHANGES

2 Kinetic Theory Kinetic = motion
Particles in a gas are considered to be hard, small spheres with an insignificant volume. The motion of particles in a gas is rapid, constant, and random.

3 All collisions between particles in a gas are perfectly elastic.
Particles in a gas only interact when they collide.

4 Temperature (in kelvins, K) is directly proportional to the average kinetic energy of the particles of a substance. Objects expand when heated because of increased vibrational motion.

5 Gas pressure is caused by the collisions of particles with an object (wall).

6 Atmospheric pressure results from the weight of air above an object.
Higher altitudes have less atmospheric pressure.

7 Standard atmospheric pressure is:
1 atm = kPa = 760 mm Hg A barometer measures atmospheric pressure.

8 Liquids Condensed states of matter – solids and liquids
In liquids KE is high enough for molecules to flow and take the shape of their container.

9 Intermolecular attractions give liquids a definite volume.

10 Evaporation – changing from liquid to vapor at the surface - cooling process

11 Condensation – warming process

12 Vapor pressure – pressure in a bubble

13 Boiling point – temperature at which the vapor pressure equals external pressure on the liquid

14

15 Gas Stoichiometry 1 mol of a gas at standard temperature and pressure (STP) = 22.4 L

16 Volume – Volume Problems
2NO + O2  2NO2 How many liters of nitrogen dioxide are produced when 34 L of O2 react?

17 What cancels?

18 Volume – Moles Problems
2NO + O2  2NO2 How many moles of nitrogen dioxide are produced when 34 L of O2 react?

19 Solids Phase Changes The general properties of solids reflect the orderly arrangement and fixed locations of their particles. Crystal - regular geometric arrangement

20 Allotropes - (diamond, graphite) 2 or more different molecular forms of the same element in the same physical state

21 Amorphous - no geometric pattern

22 Phase changes Sublimation - solid to vapor Vaporization - liquid to vapor (evaporation or boiling) Solidification - liquid to solid Melting - solid to liquid

23 A) 0.016C, 0.61 kPa B) S, L, V C) 100C; 0C

24 Ch 13 Review Notes Atmospheric pressure affects the boiling point of a liquid.

25 STP – standard temperature and pressure - 0C and 1 atm
1 atm = 760 mm Hg so…

26 Absolute zero = 0 K is the temperature the motion of particles theoretically ceases.

27 Triple point – conditions ( temperature & pressure) at which solid, liquid, and vapor (gas) can exist in equilibrium.

28 Solids are more dense than liquids and gases.
Sublimation can occur because solids have a vapor pressure.


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