Unit 2 B Matter, Energy, and Changes

Matter & Changes

Matter Is anything that has mass and volume

States: Gas – no definite shape or volume particles randomly scattered particles moving quickly in constant motion, highly compressible, low density, rapid diffusion high expansion on heating

States:Liquid no set shape definite volume particles somewhat organized particles free to move slightly compressible high density slow diffusion low expansion on heating

Properties of Liquids Viscosity – friction or resistance to motion, increases as temperature decreases Surface tension – molecules at the surface experience imbalanced attractive forces

Both gasses and liqids are fluids. This is because of weak intermolecular forces. The molecules can slide easily over each other.

States:Solid has particular shape definite volume particles very organized and close together, particles move only very slightly low compressibility high density slow diffusion low expansion on heating

Solids Intermolecular forces are strong Molecules still move Can only vibrate and revolve in place. Particles are locked in place - don’t flow. Melting point is the temperature where a solid turns into a liquid. The melting point is the same as the freezing point.

Solids When heated the particles vibrate more rapidly until they shake themselves free of each other. As they are heated the temperature doesn’t change. The energy goes into breaking bonds, not increasing motion Move differently, not faster.

Basic Types of Solids Crystalline solids – Amorphous solids -

Crystals are made of atoms arranged in highly ordered, patterns called unit cells A regular repeating three dimensional arrangement of atoms in a solid. Most solids are crystals. Break at certain angles Examples Table salt, table sugar, Emerals

Amorphous solids appear solid, but are more of a super-cooled liquid, have high viscosity, gradually soften as temperature increases lack an orderly internal structure. Think of them as super-cooled liquids. Glasses are one type. Rigid but lacking structure Do not melt- just gradually get softer. Shatter at random angles Examples: glass, and plastics

Properties of Solids Some solids are good conductors due to particles being in contact with each other and passing the energy from one to another

Physical State of Matter State of matter at room temperature depends on strength of intermolecular forces ( IM) For example, a substance with strong IM forces will be a solid while a substance with very weak IM forces will be a gas

Matter Intermolecular Forces Are the forces between neighboring molecules

Changes of State Energy and change of state… To change states, particles must overcome the attractive forces holding them together (the number of particles does not change)

Kinetic Theory and states of Matter Kinetic theory says that molecules are in constant motion. Perfume molecules moving across the room are evidence of this.

Kenetic Theory helps to explain why a gas behaves as it does. It also helps us understand the changes in physical states of matter

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles

The Kinetic Theory of Gases Makes three descriptions of gas particles A gas is composed of particles molecules or atoms Considered to be hard spheres far enough apart that we can ignore their volume. Between the molecules is empty space.

The particles are in constant random motion. Move in straight lines until they bounce off each other or the walls. All collisions are perfectly elastic

The Average speed of an oxygen molecule is 1656 km/hr at 20ºC The molecules don’t travel very far without hitting each other so they move in random directions.

Breaking intermolecular forces. Vaporization - the change from a liquid to a gas below its boiling point. Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).

Evaporation Molecules at the surface break away and become gas. Only those with enough KE escape Evaporation is a cooling process. It requires energy.

Condensation Change from gas to liquid Molecules stick together Releases energy.

Boiling Making bubbles of gas Forces liquid level to rise Must push against air pressure on the liquid.

Boiling A liquid boils when the vapor pressure = the external pressure Temperature is called the boiling point Normal Boiling point is the temperature a substance boils at 1 atm pressure. The normal boiling point of water is 100o C The temperature of a liquid can never rise above it’s boiling point Energy goes into breaking forces, not moving faster.

Changing the Boiling Point Lower the pressure (going up into the mountains). Lower external pressure requires lower vapor pressure. Easier to make bubbles Lower vapor pressure means lower boiling point. Food cooks slower.

Changing the Boiling Point Raise the external pressure (Use a pressure cooker) Raises the vapor pressure needed. Harder to make bubbles Raises the boiling point. Food cooks faster.

Different Boiling points Different substances boil at different temperatures because they have different intermolecular forces Weak forces- lower boiling point Different vapor pressures Low vapor pressure – high boiling point

Changes of State Heat of vaporization You have 18.2 moles of water. How much energy is needed to vaporize the sample? (Molar heat of vaporization for water = 40.7 kJ/mole) 740.74 kJ

Changes of State Melting You have a 278 mole block of ice. How much energy is needed to melt it? (Molar heat of fusion for water = 6.00 kJ/mole) 1668 kJ

Phase Changes Solid Gas Liquid Melting Vaporization Freezing Condensation

Solid Gas Liquid Require energy Sublimation Melting Vaporization Condensation Freezing Condensation Release energy

Temperature and Phase Change The temperature doesn’t change during a phase change. If you have a mixture of ice and water, the temperature is 0ºC At 1 atm, boiling water is 100ºC You can’t get the temperature higher until it boils

Heating Curve A graph of Energy versus temperature.

Changes of State Heating curves Describe changes of state of matter, plot of sample temperature as a function of time

Changes of State

Changes of State Phase diagrams Relates states of matter to temperature and pressure

Changes of State