Unit 2 States of Matter

Unit 2 States of Matter

Study Guide

U2L1 

Kinetic Theory of Matter

1.  All matter is made up of molecules that are in constant motion.

2. The states of matter are the physical forms in which matter can exist.  

3. The state of matter of the substance is determined by:

1.  How fast the molecules are moving.

2.  How strong the attraction is between the molecules.  

The 3 Main States of Matter:

U2L2:  

What are the 2 basic ways to change the state of matter of a substance?

1. Change the Temperature of the Substance

1. The substance can gain energy from its surroundings (heat up).  This will cause the particles to speed up.  This type of change is called endothermic change.

2. The substance can lose energy  to its surroundings (cool down).  This will cause the particles to slow down.  This type of change is called an exothermic change.

     B.  Change the Pressure Acting on the Substance

1. Increasing pressure causes particles to move closer together.

2. Decreasing pressure causes particles to move farther apart.

What are all the changes in state and what is happening in each one?

1. Freezing: L🡪S  Particles of a liquid lose energy, slow down and turn into a solid,

2.  Melting:  S🡪L   Particles of a solid gain energy,  speed up,  and turn into a liquid.

3.  Boiling:  L🡪G  Particles of a liquid gain energy, speed up and turn into a gas at the boiling point.  At sea level, pure water boils at 100^oC.  At higher elevations the boiling point of water would be lower than 100^oC because the pressure is lower.  In a pressure cooker, the boiling point of pure water is higher than 100^oC because the pressure is greater.

4.  Evaporation: L🡪G  Occurs gradually only at the surface of a liquid. Occurs at a temperature lower than the boiling point.  Occurs very slowly. 

5. Condensation:  G-🡪 L  Particles of a gas lose  energy, slow down and change into liquid.  

       Ex:  Water dripping down the outside of a cold glass of lemonade.

               Seeing your breath on cold days.

               Fogging up the windows of the bus. 

                Fogging up a mirror during a hot shower.

6.  Sublimation:  S →  G   Particles of a solid gain energy, speed up, skip the liquid state, and 

                   go directly into the gas state.  Ex:  Dry ice

7. Deposition:  G → S   Opposite of sublimation.  Particles of a gas lose energy, slow down, skip the liquid state, and go directly into the solid state Ex: Water vapor crystallizing on a super cold window (frost)

 What happens to the temperature during a change in state? (see graph, pg. 93)

           The temperature remains constant during a change in state.

 What happens to matter when a change in state occurs?

1. The energy  of the molecule changes.

2. The speed of the molecules changes.

3. The distance between the molecules changes.

4. The number and size of the  particles does NOT change.  CONSERVATION OF MASS!

5. A change in state is only a physical change NOT a chemical change.  Thus, the chemical make up of the material does NOT change.   

Why does the boiling point of water decrease at higher elevations?  There is less air pressure pushing down on the liquid making it easier for the water to change from liquid to gas so it takes less energy to boil. 

Why does the boiling point of water increase in a pressure cooker?  The increase in pressure makes it harder for the water to change from a liquid to a gas so it takes more energy for the water to boil. This principle explains why cooking times can vary significantly depending on the method used, as higher pressure allows for higher temperatures without boiling.